Abstract: To compare intraocular pressure (IOP) measurements after penetrating keratoplasty (PK) using Goldmann applanation tonometry (GAT; Haag-Streit USA), TonoPen XL (Reichert Inc), Pascal Dynamic Contour tonometer (PDCT; Swiss Microtechnology AG), and Ocular Response Analyzer (ORA; Reichert Inc) and to analyze effects and correlation of corneal thickness and curvature on these measurements.
Abstract: To evaluate the usefulness of the central corneal thickness (CCT)-based correction formulae for stratified CCT groups, with intraocular pressure (IOP) from the Pascal dynamic contour tonometer (PDCT) as the reference standard.
Abstract: This paper aims to review the current methods available for the measurement of intraocular pressure after myopic laser in situ keratomileusis for the correction of myopia. Searches were performed for studies that assessed or compared various methods of intraocular pressure assessment. There were 20 eligible studies that explored the use of pneumotonometry, pressure phosphene tonometry, rebound tonometry, dynamic contour tonometry, statistical modeling, mathematical formulae, ocular response analyzer and even measuring intraocular pressure on the nasal cornea. Our review shows that an ideal method would be one that is independent of corneal factors. Dynamic contour tonometry and pressure phosphene tonometry held promise in research settings. More studies need to be done to validate the new methods of intraocular pressure assessment, especially in glaucoma patients. It is important to empower laser in situ keratomileusis patients with knowledge of these difficulties and potential implications for the future.
Abstract: To compare corneal hysteresis (CH) and corneal resistance factor (CRF) between normal eyes and eyes with keratoconus correcting for the effect of central corneal thickness (CCT) and to estimate keratoconus detection sensitivity and specificity of these parameters.
Abstract: An examination of studies that have assessed corneal biomechanical performance using the Ocular Response Analyzer (ORA: Reichert Ophthalmic Instruments, Depew, NY) raises some questions regarding the influence of measurement variables and the interpretation of the findings obtained with this instrument. This analysis of those questions describes additional factors which do or may contribute to the assessment of corneal hysteresis (CH).
Abstract: To evaluate corneal hysteresis (CH) and corneal resistance factor (CRF) in keratoconic (KC) eyes before and after corneal collagen cross-linking (CXL). Furthermore, to determine potential correlations with a series of corneal and demographic factors.
Abstract: To investigate the in vivo, corneal, biomechanical changes after corneal collagen cross-linking (CXL) using the Ocular Response Analyzer (ORA) in patients with keratoconus and post-laser in situ keratomileusis (LASIK) ectasia.
Abstract: Several reports have revealed a difference in various populations regarding the variability of intraocular pressure (IOP) and corneal hysteresis (CH). This retrospective study was created to determine a profile for U.S. Veterans in a large outpatient clinical setting. OVERVIEW AND METHODOLOGY: The objective was to evaluate a random cohort of patient records in this clinical setting to determine the mean and standard deviation (SD) of the following parameters: Goldmann-correlated IOP (IOPg), CH, waveform score, and central corneal thickness from the Reichert Ocular Response Analyzer.
Abstract: We investigated the correlation between central corneal thickness (CCT) and corneal hysteresis (CH) and their relationship with the rate of visual field (VF) change.
Abstract: Purpose. To investigate biomechanical parameters of the cornea measured with ocular response analyzer (ORA) in myopic eyes with high axial length and the relationship between these parameters and axial length (AL). Methods. A total of 165 eyes of 165 consecutive patients were included. Eyes with AL greater than 26 mm were named group 1 and eyes with AL shorter than 26 mm were named group 2. Axial length and keratometric values were measured by intraocular lens (IOL) Master optical biometry. Metrics of corneal biomechanical properties, including corneal hysteresis (CH) and corneal resistance factor (CRF), were measured with the ORA. The ORA also determined the values of intraocular pressure (IOPg) and corneal compensated IOP (IOPcc). Results. The mean age of total subjects was 43.0 ± 15.6 years. Eighty-three eyes were included in group 1; 82 eyes were included in group 2. The CH and CRF of group 1 were significantly lower than group 2. The IOPcc was significantly higher in group 1 than group 2. When group 1 and group 2 were combined for analysis, CH was negatively correlated with age. Both CH and CRF were significantly correlated with SE. However, CH and CRF were negatively correlated with AL. Also, there was significant correlation between AL and IOPcc (p<0.05). Conclusions. Highly myopic eyes showed decreased CH and CRF. As the AL increased the IOPcc also increased and the CH decreased. We conclude that the biomechanical properties of the cornea change with elongation of the eye and this may have an impact on IOP measurement.
Abstract: The aim of this work was to investigate the differences in corneal biomechanical parameters between healthy and exfoliation syndrome (EXS) and exfoliative glaucoma (EXG) patients.
Abstract: Several studies have shown that administration of granulocyte-colony stimulating factor (G-CSF) is followed by an increase of white blood cell (WBC) count. There is evidence from other vascular beds that an increase in WBC count impairs blood flow regulation especially in the microcirculation. Whether this also holds true for the ocular circulation is yet unknown. In the following trial we investigated whether an increase in WBC count alters the oxygen induced vasoconstriction of retinal vessels.
Abstract: To evaluate corneal biomechanical properties across the glaucoma spectrum and study the relationship between these measurements and intraocular pressure measured by Goldmann applanation tonometry (GAT-IOP) and central corneal thickness (CCT).
Abstract: To evaluate central corneal thickness (CCT) and ocular biomechanical properties in patients before and after clear corneal phacoemulsification.
Abstract: To investigate the accuracy of intraocular pressure (IOP) as measured by a Reichert Ocular Response Analyzer (ORA), as well as the relationship between central corneal thickness (CCT) and IOP as measured by ORA, Goldmann applanation tonometry (GAT), and dynamic contour tonometry (DCT).
Abstract: To evaluate by means of the Ocular Response Analyzer (ORA) the biomechanical changes that follow intracorneal ring segment (ICRS) implantation and to develop a predicting model for the postoperative visual outcome, considering these biomechanical changes and other clinical parameters.
Abstract: PURPOSE: To perform advanced analysis of the corneal deformation response to air pressure in keratoconics compared with age- and sex-matched controls. METHODS: The ocular response analyzer was used to measure the air pressure-corneal deformation relationship of 37 patients with keratoconus and 37 age (mean 36 ± 10 years)- and sex-matched controls with healthy corneas. Four repeat air pressure-corneal deformation profiles were averaged, and 42 separate parameters relating to each element of the profiles were extracted. Corneal topography and pachymetry were performed with the Orbscan II. The severity of the keratoconus was graded based on a single metric derived from anterior corneal curvatures, difference in astigmatism in each meridian, anterior best-fit sphere, and posterior best-fit sphere. RESULTS: Most of the biomechanical characteristics of keratoconic eyes were significantly different from normal eyes (P < 0.001), especially during the initial corneal applanation. With increasing keratoconus severity, the cornea was thinner (r = -0.407, P < 0.001), the speed of corneal concave deformation past applanation was quicker (dive; r = -0.314, P = 0.01), and the tear film index was lower (r = -0.319, P = 0.01). The variance in keratoconus severity could be accounted for by the corneal curvature and central corneal thickness (r = 0.80) with biomechanical characteristics contributing an additional 4% (total r = 0.84). The area under the receiver operating characteristic curve was 0.919 ± 0.025 for keratometry alone, 0.965 ± 0.014 with the addition of pachymetry, and 0.972 ± 0.012 combined with ocular response analyzer biomechanical parameters. CONCLUSIONS: Characteristics of the air pressure-corneal deformation profile are more affected by keratoconus than the traditionally extracted corneal hysteresis and corneal resistance factors. These biomechanical metrics slightly improved the detection and severity prediction of keratoconus above traditional keratometric and pachymetric assessment of corneal shape.
Abstract: BACKGROUND: The aim of this study was to determine a threshold waveform score (WS) for the best score value (BSV) in the Ocular Response Analyzer (ORA). METHODS: Retrospective study. One hundred and thirty-three healthy adults were recruited. Measurements were done with the ORA 2.04. RESULTS: Two hundred and sixty-six eyes were analyzed. Mean age was 56.49 ± 15.97 years. The mean waveform score of the BSV was 7.39 ± 1.32. The waveform scores ranged from 2.8 to 9.7. Kolmogorov-Smirnov test for normality was significant (p ≤ 0.0001). Linear regression showed a significant positive correlation between IOPg (measured with the ORA) and IOP measured with Goldmann applanation tonometry (p ≤ 0.0001), as well as significant negative correlation between the difference IOPg-IOP Goldmann and waveform score of the BSV values. Threshold estimation considering 95 % confidence interval was 7.23. Meanwhile, threshold estimation considering the difference IOPg-IOP Goldmann, for 3 mmHg, was 6.7. CONCLUSIONS: When using the ORA device, we recommend that clinicians try to obtain several waveform score measurements of 7 or above. Waveform scores lower than 7 may render less reliable results.
Abstract: Purpose: To evaluate corneal biomechanical properties and intraocular pressure (IOP) after photorefractive keratectomy (PRK) with or without mitomycin-C (MMC) 0.02% in myopic eyes. Methods: In this prospective, comparative interventional case series, 33 right eyes of 33 patients were included. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated IOP (IOPg), and cornea-compensated IOP (IOPcc) were measured using ocular response analyzer (ORA) before and 3 months after PRK. IOP was determined using Goldmann applanation tonometry (GAT). The pre- and post-operative values were compared. Effects of ablation depth, optical zone (OZ) and duration of MMC application on corneal biomechanics were examined. Results: Mean ablation depth was 56.6 ± 20.8 μm. Postoperatively, there was a significant reduction in corneal biomechanics and IOP readings by the GAT and ORA. Ablation depth was significantly associated with percentage change in CH (P = 0.021), CRF (P = 0.001), and IOP GAT (P < 0.001). However, the size of OZ and duration of MMC application did not have any correlation with these parameters. The percentage change in IOP GAT and IOPg but not IOPcc was significantly associated with percentage change in CH and CRF. Conclusions: The corneal biomechanical strength significantly reduced after PRK which is associated to the amount of ablation. However, the OZ and the duration of MMC application did not affect these parameters. IOPcc appeared to be less dependent on altered corneal properties compared to IOPg and IOP GAT.
Abstract: Purpose: To evaluate the repeatability of corneal hysteresis (CH) and corneal resistance measurements as well as the consistency of the four shots within each measurement using the ocular response analyzer (ORA, Reichert Ophthalmic Instruments, Depew, NY) and to generate a pool of data of a normal population. Methods: A total of 45 eyes from 45 healthy volunteers without ocular pathologies and normal visual acuity were enrolled in this study. A sequence of five consecutive measurements was performed with each patient with the ORA. The biomechanical properties of the cornea in terms of CH and corneal resistance factor (CRF) were recorded, as well as the Goldmann-correlated IOP (IOPg) and cornea correlated IOP (IOPcc). The trend in each measurement sequence was analyzed and Cronbach's α was derived for the repeatability. The average of four shots within each measurement was compared with the best signal value (BSV) provided by the internal data processing of the ORA. Results: Mean value for CH was 11.58 and BSV was 11.55. For CRF, mean value was 11.21 and BSV was 11.28. No significant difference was found between the average value and the BSV of one measurement (p > 0.05). No significant difference was found between the average value and the BSV of the five consecutive measurements, only IOPg showed a significant difference (p = 0.017), average value of IOPg is higher than BSV. Within a sequence of five measurements for each individual, the average values of the four shots per measurement for IOPg and IOPcc are decreasing by 1.19 and 1.05 mmHg on average. The repeatability test revealed good results for CH and CRF (all α are higher than 0.9). Conclusion: The ORA provides, beside intraocular pressure additional, information about the biomechanical properties of the cornea such as hysteresis and resistance. It proves to yield good repeatability for corneal hysteresis and resistance in normal subjects.
Abstract: OBJECTIVE: To assess the agreement of tonometers available for clinical practice with the Goldmann applanation tonometer (GAT), the most commonly accepted reference device. DESIGN: A systematic review and meta-analysis of directly comparative studies assessing the agreement of 1 or more tonometers with the reference tonometer (GAT). PARTICIPANTS: A total of 11 582 participants (15 525 eyes) were included. METHODS: Summary 95% limits of agreement (LoA) were produced for each comparison. MAIN OUTCOME MEASURES: Agreement, recordability, and reliability. RESULTS: A total of 102 studies, including 130 paired comparisons, were included, representing 8 tonometers: dynamic contour tonometer, noncontact tonometer (NCT), ocular response analyzer, Ocuton S, handheld applanation tonometer (HAT), rebound tonometer, transpalpebral tonometer, and Tono-Pen. The agreement (95% limits) seemed to vary across tonometers: 0.2 mmHg (-3.8 to 4.3 mmHg) for the NCT to 2.7 mmHg (-4.1 to 9.6 mmHg) for the Ocuton S. The estimated proportion within 2 mmHg of the GAT ranged from 33% (Ocuton S) to 66% and 59% (NCT and HAT, respectively). Substantial inter- and intraobserver variability were observed for all tonometers. CONCLUSIONS: The NCT and HAT seem to achieve a measurement closest to the GAT. However, there was substantial variability in measurements both within and between studies. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.
Abstract: To evaluate and compare corneal biomechanical waveform parameters between keratoconic and post-femtosecond laser in situ keratomileusis (LASIK).
Abstract: We sought to determine whether corneal biomechanical parameters are predictive of reduction in axial length after anti-metabolite trabeculectomy.
Abstract: PURPOSE:: Among other corneal biomechanical properties, Goldmann applanation tonometry (GAT) has been shown to depend on corneal edema. New tonometry devices have been designed, such as the Tono-Pen XL, iCare, and ocular response analyzer (ORA), to measure the intraocular pressure (IOP) accurately. This study aims to investigate the influence of corneal edema on the accuracy of these IOP-measuring devices in an in vitro model. METHODS:: A model of an artificial anterior chamber was developed using a guided trephination system. Eight donor corneas not suitable for keratoplasty were clamped into this artificial anterior chamber. All corneas showed signs of stromal edema. Intracameral pressure (ICP) was adjusted manometrically to 10, 20, 30, 40, and 50 mm Hg. The central corneal thickness (CCT) was determined by ultrasonic pachymetry. For each manometrically defined ICP, tonometry was performed using the iCare, Tono-Pen XL, GAT, and ORA. RESULTS:: The mean CCT increased from 616.1±29.6 µm to 626.9±36.1 µm. At 10 mm Hg, GAT yielded a higher ICP than those manometrically adjusted (10.4±3.3 mm Hg); at all other ICP levels, GAT yielded lower ICP levels than those adjusted. The Tono-Pen XL and iCare showed the greatest difference at 10 mm Hg, with the Tono-Pen XL yielding a value of 14.0±4.0 mm Hg and the iCare yielding a value of 12.5±2.6 mm Hg. All other results of the 2 devices fell within a range of ±2 mm Hg from the adjusted ICP. The ORA provided accurate results only at "physiological" ICP levels with a maximum difference of 2.6 mm Hg at 30 mm Hg. At higher ICP levels, corneal hysteresis decreased significantly with increasing ICP. None of the measurement devices revealed a statistically relevant dependence on CCT in this experimental setting. CONCLUSIONS:: The Tono-Pen XL and the iCare yielded the most accurate ICP values across all the adjusted ICP values. This may be because of their relatively small contact area with the cornea and, consequently, greater independence from corneal biomechanical properties. The ORA yielded accurate measurement results only at physiological ICP levels. As anticipated, GAT underestimated ICP. The Tono-Pen XL and the iCare should therefore be used to determine IOP in patients suffering from corneal edema, such as bullous keratopathy or Fuchs endothelial dystrophy.
Abstract: PURPOSE:: To estimate the influence of corneal properties on intraocular pressure (IOP) differences between an air-puff tonometer (NT530P; Nidek) and the Goldmann applanation tonometer (Haag-Streit). PATIENTS AND METHODS:: The influence of central corneal thickness (CCT), keratometry, and Ocular Response Analyzer (Reichert) measurements of corneal viscoelasticity [corneal hysteresis (CH) and corneal resistance factor (CRF)] on IOP differences between tonometers was evaluated. RESULTS:: The CRF was calculated to be the best predictor of the differences in IOP readings between tonometers (r=0.23; P<0.001), followed by CCT (r=0.15; P=0.003) and CH (r=0.14; P=0.003). Keratometry performed very poorly as lone predictor of IOP differences. In a multiple regression model, CRF, CH, and CCT together accounted for 25% (r=0.25; P<0.01) of the variance in IOP reading differences between tonometers. CONCLUSIONS:: Corneal resistance to applanation induced by either contact or noncontact tonometers was calculated to be the most determinant factor in influencing IOP differences between applanation tonometers.
Abstract: PURPOSE: To measure corneal graft biomechanical properties after penetrating keratoplasty (PKP) in a group of keratoconic eyes using the ocular response analyzer (ORA) and to evaluate the relationship between donor size, donor-recipient disparity and central graft thickness (CGT), and ORA parameters. METHODS: This cross-sectional study was conducted on 34 eyes of 34 keratoconus patients who had undergone PKP. Corneal hysteresis (CH), corneal resistance factor (CRF), and cornea-compensated intraocular pressure were measured at least 6 months after complete suture removal. Two groups of donor-recipient disparity (0.25 vs. 0.50 mm) were compared using the independent t test. Multivariate regression analysis was used to investigate the correlation of donor trephine size and CGT with ORA parameters. Factors influencing intraocular pressure measured with the Goldmann applanation tonometer (IOP GAT) after PKP were determined using multiple regression analysis. RESULTS: Mean patient age and follow-up period were 29.6 ± 6.2 years and 82.4 ± 59.6 months, respectively. Mean CGT, CH, and CRF were 564.7 ± 36.9 μm, 10.1 ± 2.1 mm Hg, and 10.0 ± 2.3 mm Hg, respectively. CH and CRF had a significant positive correlation with donor trephine size and CGT. Significantly greater values of CH and CRF were observed in the 0.5-mm disparity group compared with the 0.25-mm disparity group. Among the studied parameters, only CH, CRF, and cornea-compensated intraocular pressure had a significant positive correlation with IOP GAT. CONCLUSION: Graft biomechanics seem to be closer to normal values with larger grafts and greater donor-recipient disparity. These metrics had a significant correlation with IOP GAT after PKP.
Abstract: : To investigate the possible covariations between diurnal changes in Goldmann applanation tonometry (GAT) estimates of intraocular pressure (IOP), central corneal thickness (CCT), central corneal radius, and ocular response analyzer measures of corneal hysteresis and corneal resistance factor (CRF).
Abstract: : To assess the biomechanical and keratometric effects and the safety of treatment of progressive keratoconus with UV-riboflavin collagen cross-linking (CXL).
Abstract: PURPOSE.: To evaluate the relative influences of several demographic, ocular, and systemic parameters on corneal hysteresis (CH). METHODS.: This is a prospective, observational, cross-sectional study using subjects recruited from consecutive Albuquerque VAMC eye clinic patients. We classified eligible subjects as primary open-angle glaucoma (POAG), ocular hypertension, glaucoma suspect, or normal. We used the Ocular Response Analyzer, Pascal Dynamic Contour Tonometer, and Goldmann applanation tonometer to obtain intraocular pressure (IOP), CH, corneal resistance factor, and ocular pulse amplitude values. We also obtained corneal curvature, central corneal thickness (CCT), axial length, retinal nerve fiber layer thickness, clinical cup/disc ratio (CDR) estimates, and standard automated perimetry metrics (mean defect, pattern standard deviation). We gathered glycosylated hemoglobin (A1C) data through chart review. Multivariate regression analyses were used to determine independent relationships between CH and the other parameters. RESULTS.: Three hundred seventeen eyes in 317 subjects were studied (116 POAG, 87 ocular hypertension, 47 glaucoma suspect, and 67 normal). In univariate regression analysis, CH varied directly with CCT (β = 0.39, p < 0.001), corneal curvature (β = 0.16, p = 0.01), corneal resistance factor (β = 0.57, p < 0.001), A1C (β = 0.15, p = 0.01), mean defect (β = 0.29, p < 0.001), and retinal nerve fiber layer (β = 0.31, p < 0.001). Factors inversely related to CH were age (β = -0.22, p < 0.001), IOP (β = -0.29, p < 0.001), ocular pulse amplitude (β = -0.11, p = 0.04), CDR (β = -0.34, p < 0.001), and pattern standard deviation (β = -0.29, p < 0.001). CH was lower in POAG compared with the other diagnostic groups. In multivariate analysis, CH was independently associated with age, IOP, CCT, A1C, glaucoma diagnosis, and CDR. Of these factors, CCT and IOP demonstrated twice as much influence on CH compared with the other four factors. CONCLUSIONS.: Although this study identified six separate variables that independently influence CH values, the overall r value indicates that these variables together only explain 40% of CH variability. These results suggest that other significant sources of variability exist and deserve investigation.
Abstract: PURPOSE:: To examine factors that influence intraocular pressure (IOP) measurement agreement between Goldmann applanation (GAT), Ocular Response Analyzer (ORA), and Pascal Dynamic Contour tonometers (DCT). PATIENTS AND METHODS:: In subjects who were diagnosed with primary open-angle glaucoma, ocular hypertension, glaucoma suspect, and normal, we used ORA, DCT, and GAT to obtain corneal hysteresis (CH), corneal resistance factor (CRF), ocular pulse amplitude, and 4 IOP values (ORA-IOPcc; ORA-IOPg; DCT-IOP; and GAT-IOP.) We also obtained corneal curvature, corneal thickness, axial length, retinal nerve fiber layer thickness, visual field parameters, diabetes diagnostic status, and topical IOP-lowering treatment data. Analysis of variance, Bland-Altman, and regression analyses were used to examine IOP agreement and associated factors. RESULTS:: In 243 eyes of the 243 subjects, mean DCT-IOP (18.73±4.92) was not different from mean ORA-IOPcc (18.96±5.41) but both were significantly higher than ORA-IOPg (16.97±5.49) and GAT-IOP (16.37±4.97). In multivariate regression models, intermethod differences between IOPg, IOPcc, and DCT-IOP were explained almost completely by variations in CH, CRF, and level of IOP (r=0.98 to 0.99); conversely, intermethod variability between GAT-IOP and the other 3 IOP metrics was only partially explained by the factors evaluated in this study (r=0.31 to 0.65). CONCLUSIONS:: Consistent with other studies, we found that the 4 IOP variables examined in this study are not interchangeable. The most consistent confounders of IOP measurement agreement were the ORA-measured corneal parameters, CH and CRF. Thus, accounting for these factors may be important in efforts to obtain accurate transcorneal estimates of IOP.
Abstract: The aim of this study was to evaluate the accuracy of intraocular pressure (IOP) values from the new non-contact tonometer (NCT) Reichert R7 by comparing results with those from Goldmann applanation tonometry (GAT) and the Reichert Ocular Response Analyzer (ORA). Other ocular dimensions were assessed to evaluate their potential influence on the IOP values obtained.
Abstract: To examine the interrelationships among the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY), Goldmann applanation tonometer (GAT), and corneal geometry measurements in a young, healthy sample.
Abstract: Purpose: To identify differences in corneal hysteresis (CH) between primary open-angle glaucoma (POAG), pseudoexfoliative glaucoma patients (PXSG) and a healthy control group. Methods: In this retrospective study, CH was measured with the Ocular Response Analyzer. 90 subjects were evaluated, 30 subjects in each group. One eye per subject was analyzed. Results: In normal eyes, POAG and PXSG, CH was 9.8 ± 1.6, 9.0 ± 1.9 and 8.0 ± 1.5 mm Hg, respectively. CH was significantly lower in PXSG patients than in POAG (p = 0.042) and normal patients (p = 0.0001), but no significance was found between the POAG and the normal group (p = 0.23). Conclusion: CH differs in the different groups and might be considered in glaucoma evaluation. Further studies with larger sample sizes are needed.
Abstract: To compare intraocular pressure (IOP) measurements obtained using the Goldmann applanation tonometer (GAT; Haag-Streit), the Tono-Pen XL (Reichert, Inc), and the ocular response analyzer (ORA; Reichert Ophthalmic Instruments), and to determine the influence of corneal factors on IOP measurements in eyes that had undergone penetrating keratoplasty (PK).
Abstract: To compare intraocular pressure (IOP) measured using the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY) with that measured using the Goldmann applanation tonometer (GAT) in keratoconic eyes after deep anterior lamellar keratoplasty (DALK) and evaluate the influence of central graft thickness (CGT), corneal astigmatism, corneal hysteresis (CH), and corneal resistance factor (CRF) on the IOP measurements.
Abstract: To investigate the changes in Goldmann applanation tonometry (GAT) and Ocular Response Analyzer (ORA) measurements with corneal edema induced by contact lenses.
Abstract: To evaluate the clinical features of keratoconus taking into consideration anterior corneal aberrations, internal astigmatism, and corneal biomechanical properties and to define a new grading system based on visual limitation.
Abstract: To investigate variations in corneal hysteresis (CH) and corneal resistance factor (CRF) and their ocular and systemic associations in Chinese adults.
Abstract: To evaluate the clinical outcomes after implantation of the MyoRing (DIOPTEX GmBH, Linz, Austria) by means of femtosecond laser technology in eyes with corneal ectasia.
Abstract: The correct interpretation of measured tonometric values has become more and more complex in recent years. Large clinical studies have shown that an average central corneal thickness (CCT) of 550 µm can be assumed for the general population. Since the standard Glodmann applanation tonometry is based on a central corneal thickness of 520 µm, mathematical correction formula have been discussed for calculation of the true intraocular pressure. Newer tonometry devices, e. g. the dynamic contour tonometry (DCT) which seems to be independent from CCT, or the Ocular Response Analyzer® (ORA), taking into account the biomechanical properties of the cornea, have been designed to measure intraocular pressure (IOP). In this article, several IOP measurement devices and their clinical relevance for a correct and feasible determination of the IOP are discussed.
Abstract: Diabetic retinopathy is characterized by morphological changes in the retina secondary to disturbances in retinal blood flow. It has been shown that antihypertensive treatment has a protective effect on the development of diabetic retinopathy, and evidence suggests that inhibitors of the renin-angiotensin system have a protective effect beyond the antihypertensive effect. The background for this additional effect is unknown but might be related to an effect on retinal autoregulation.
Abstract: To evaluate if the ocular pulse amplitude (OPA) (the difference between systolic and diastolic intraocular pressure) is associated with the measurement variability of IOPg [Goldmann-correlated intraocular pressure (IOP)], IOPcc (corneal compensated IOP), corneal hysteresis (CH), and corneal resistance factor (CRF) obtained from the ocular response analyzer (ORA).
Abstract: To compare corneal hysteresis (CH) and corneal resistance factor (CRF) measured with the Ocular Response Analyzer (ORA) in patients with primary open-angle glaucoma (POAG), patients with ocular hypertension (OHT), and normal subjects (NL); and to assess correlations of CH and CRF with corneal-compensated intraocular pressure (IOPcc), Goldmann applanation tonometry (GAT), glaucoma type, central corneal thickness (CCT), previous filtering procedure, and antiglaucoma medications.
Abstract: To analyse the reproducibility of corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg) and corneal-compensated intraocular pressure (IOPcc) obtained with the ocular response analyzer (ORA).
Abstract: To compare corneal hysteresis (CH) and corneal resistance factor (CRF) in eyes with keratoconus with a central corneal thickness (CCT) ≥ 520 μm with CH and CRF in matched controls, and to estimate the sensitivity and specificity of these parameters for discriminating between the two groups.
Abstract: To evaluate corneal hysteresis (CH) and intraocular pressure (IOP) measured by the Ocular Response Analyzer in Chinese subjects with primary angle-closure glaucoma (PACG), assess their relationship with Goldmann applanation tonometry (GAT) measurements, and compare this with subjects with primary open-angle glaucoma (POAG) and normal controls.
Abstract: To compare the intraocular pressures (IOPs) obtained with the IOPen rebound tonometer, Goldmann applanation tonometer (GAT) and the ocular response analyzer (ORA) and investigate the effects of corneal biomechanical properties on IOPen measurements.
Abstract: The purpose of this study is to develop a 3D patient-specific finite element model (FEM) of the cornea and sclera to compare predicted and in vivo refractive outcomes and to estimate the corneal elastic property changes associated with each procedure. Both eyes of a patient who underwent laser-assisted in situ keratomileusis (LASIK) for myopic astigmatism were modeled. Pre- and postoperative Scheimpflug anterior and posterior corneal elevation maps were imported into a 3D corneo-scleral FEM with an unrestrained limbus. Preoperative corneal hyperelastic properties were chosen to account for meridional anisotropy. Inverse FEM was used to determine the undeformed corneal state that produced <0.1% error in anterior elevation between simulated and in vivo preoperative geometries. Case-specific 3D aspheric ablation profiles were simulated, and corneal topography and spherical aberration were compared at clinical intraocular pressure. The magnitude of elastic weakening of the residual corneal bed required to maximize the agreement with clinical axial power was calculated and compared with the changes in ocular response analyzer (ORA) measurements. The models produced curvature maps and spherical aberrations equivalent to in vivo measurements. For the preoperative property values used in this study, predicted elastic weakening with LASIK was as high as 55% for a radially uniform model of residual corneal weakening and 65% at the point of maximum ablation in a spatially varying model of weakening. Reductions in ORA variables were also observed. A patient-specific FEM of corneal refractive surgery is presented, which allows the estimation of surgically induced changes in corneal elastic properties. Significant elastic weakening after LASIK was required to replicate clinical topographic outcomes in this two-eye pilot study.
Abstract: To investigate biomechanical changes after corneal cross-linking (CXL) with riboflavin/ultraviolet-A (UVA) in keratoconus using the recently developed Ocular Response Analyzer (ORA, Reichert Technologies) software.
Abstract: To determine whether alterations in architecture cause corneal biomechanical changes after simultaneous cataract surgery and limbal relaxing incisions (LRIs).
Abstract: Purpose:  High intraocular pressure (IOP) and glaucoma are often suspected in patients with mucopolysaccharidosis (MPS). To determine corneal hysteresis (CH) and IOP in children with mucopolysaccharidosis I-Hurler (MPS I-H) and MPS VI. Methods:  Clinical measurements with ocular response analyzer (ORA). Results:  In seven patients, five with MPS I-H treated with stem cell transplantation (SCT), and two with MPS VI, one treated with SCT and the other with enzyme therapy, the IOP was examined with ORA. Ocular response analyzer measurements were made at a median age of 8.7 years in the patients with MPS I-H and at a median age of 9.3 years in the patients with MPS VI. Earlier measurements had raised suspicion of high IOP in one patient. The ORA showed an increased CH and a falsely high IOP values in all 14 eyes. The recalculated IOPs were normal in all 14 eyes. Mild to severe corneal opacities were present in all 14 eyes. Optic disc areas, borders and cupping were clinically normal in the 12 of 14 eyes that were possible to examine. Severe corneal opacities hampered optic disc evaluation in the older patient with MPS VI. Three eyes in two patients had normal thickness of the retinal nerve fibre layer measured with scanning laser polarimetry with corneal compensation (GDx VCC). No patient was diagnosed or treated for glaucoma. Conclusion:  The IOPs are often falsely high because of an increased resistance of the cornea and correlate to the extent of corneal clouding. In this small, cross-sectional study, it appears that corneal resistance is directly correlated with corneal clouding, although a longitudinal study that evaluates resistance as the cornea clears with treatment would provide more direct evidence that corneal deposits are directly related to resistance. A correct measured IOP can avoid unnecessary medical or surgical hypotensive treatment.
Abstract: Purpose:  To evaluate the effect of routine phacoemulsification in corneal viscoelastic properties determined by corneal hysteresis (CH) and central corneal thickness (CCT) and to explore the impact of phaco energy on the above parameters. Methods:  Forty-one eyes of 41 patients undergoing cataract surgery were enrolled in this prospective study. CH and CCT were measured preoperatively, 1 day and 1 week postoperatively. CCT measurement was performed using a non-contact optical pachymeter followed by ocular response analyzer (ORA) examination. Intraoperatively ultrasound time, average phaco power and effective phaco time (EPT) were recorded. Results:  Mean CH was 10.05 ± 1.86 mmHg preoperatively, 8.25 ± 1.85 mmHg 1 day and 9.12 ± 1.37 mmHg 1 week postoperatively (p < 0.001). The mean CCT was 534 ± 37.33 μm preoperatively, 592.22 ± 46.34 μm 1 day and 563.21 ± 49.84 μm 1 week postoperatively (p < 0.001). CCT and CH were statistically significantly correlated preoperatively (p = 0.01, r = 0.396). This correlation was not sustained on the first postoperative day (p = 0.094, r = 0.265) and was re-established 1 week postoperatively (p = 0.002, r = 0.568). On the first postoperative day, the CCT increase was positively correlated with EPT (p = 0.009, r = 0.404), which was not found between CH change and EPT. Conclusion:  Structural corneal alterations following cataract surgery resulted in a statistical change in CH and CCT. These two parameters responded in a different manner that clearly demarcates their different nature. On the first postoperative day, CCT increase was correlated at a statistically significant level with intraoperative EPT. This correlation was not found with CH reduction. Other factors, besides cornea oedema or phacoemulsification energy, could be responsible for this CH modification.
Abstract: We report a case of corneal ectasia in a 25-year-old man after myopic laser in situ keratomileusis in which a complete characterization of the corneal structure was performed by means of a Scheimpflug photography-based system. The patient presented in the ectatic eye with a subjective refraction of +0.50 to 6.00 × 100°, which with correction gave a visual acuity of 20/25. With the topographic analysis, corneal shapes from both corneal surfaces at the four different quadrants were found to be complementary, maintaining the meniscus-shaped profile of the cornea. This correlation between the anterior and posterior corneal surfaces was also confirmed with an optical tomography evaluation. Corneal biomechanics was also evaluated by means of the Ocular Response Analyzer (Reichert), which confirmed the biomechanical alteration. In summary, biomechanical changes leading to corneal ectasia in this case affected the global corneal structure, inducing alterations in the shape of both anterior and posterior corneal surfaces.
Abstract: To evaluate and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in healthy eyes with a central corneal thickness (CCT) < 505 µm with CH and CRF in gender-, age-, and CCT-matched keratoconus cases, and to estimate the sensitivity and specificity of these parameters for discriminating between the two groups.
Abstract: Habitual smoking is a risk factor for a variety of vascular diseases, including ocular pathologies. In the current study, we set out to investigate whether the regulation of retinal vascular tone is impaired in habitual smokers. For this purpose, vascular reactivity was tested during flicker light induced vasodilatation in smokers and in a non-smoking control group.
Abstract: To evaluate the agreement between intraocular pressure (IOP) readings measured by the Ocular Response Analyzer (ORA) and corrected Goldmann applanation tonometry (cGAT), derived from the "gold standard" for the clinical measurement of IOP, in eyes of subjects who have undergone laser in situ keratomileusis (LASIK). The effects of corneal biomechanical properties on IOP were also evaluated.
Abstract: Purpose:  To compare corneal hysteresis (CH) and corneal resistance factor (CRF) measured with the Ocular Response Analyzer(®) tonometer (ORA) between (i) African normals and treated primary open-angle glaucoma (POAG) patients and (ii) between normals and treated POAG Caucasians. To analyse the correlation of CH and CRF with visual field (VF) defects in the two groups. Methods:  This comparative study included 59 African (29 (POAG), 30 normals) and 55 Caucasians (30 POAG and 25 normals) subjects. Goldmann applanation tonometry (GAT) and ORA measurements were performed in a randomized sequence. Visual field was tested with the Swedish interactive threshold algorithms standard strategy of the Humphrey perimeter. Hoddap classification was used to estimate the severity of VF defects. Results:  Primary open-angle glaucoma Africans were younger than POAG Caucasians (p < 0.001). Goldmann applanation tonometry and central corneal thickness (CCT) did not differ significantly between the four subgroups. African normals had lower CH than Caucasian controls (p < 0.001). CH was 9.2 ± 1.1 and 8.3 ± 1.7 mmHg respectively in POAG Caucasians and Africans (p < 0.001). African controls had higher ORA corneal-compensated intraocular pressure (IOPcc) than Caucasian controls (p < 0.001). Primary open-angle glaucoma Africans had higher IOPcc values than Caucasian POAGs (p < 0.001). CH and IOPcc were associated with race (p < 0.001) but not with CCT. Based on mean deviation values (MD), POAG Africans had more severe VF defects. CH was correlated with MD (r = 0.442; p = 0.031) and severity of VF defects only in POAG Africans (r = -0.464; p = 0.013). Conclusions:  African normal subjects and POAG patients had an altered CH, which is associated with a significant underestimation of GAT IOP. This may potentially contribute to the earlier development and greater severity of glaucoma damage in Africans compared with Caucasians at diagnosis.
Abstract: To estimate the ability of the Ocular Response Analyzer parameters to aid in the diagnosis of keratoconus in pre-laser in situ keratomileusis (LASIK) patients.
Abstract: PURPOSE:: To evaluate the inter-examiner reproducibility of Ocular Response Analyzer (ORA) parameters in healthy subjects using the waveform score (WS) for quality control of acquisition. PATIENTS AND METHODS:: Fifteen healthy subjects had their intraocular pressure (IOP) measured with ORA by 2 masked examiners. An acquisition protocol that aimed at obtaining 4 reliable measurements in each eye with WS≥6 and with as few repeated measurements as possible was employed, whereas a maximum of 8 measurements per eye was allowed. Additional good quality criteria included symmetrical force-in and force-out applanation signal peaks on the ORA waveform and few or no distortions of the applanation signal curve. Only the right eyes were included in the analysis. Examiners were trained but not experienced. The inter-examiner reproducibility of ORA parameters was assessed using the intraclass correlation coefficient (ICC). Mean values of the best 4 measurements were considered in analysis. RESULTS:: ICC including the best 4 measurements per eye was high for all ORA parameters. Specifically, ICC for Goldmann-correlated IOP was 0.961, for corneal-compensated IOP was 0.962, for corneal resistance factor was 0.987, and for corneal hysteresis was 0.988. Similar reproducibility was found when only the 3 best measurements per eye were included in the analysis. CONCLUSIONS:: The protocol for IOP measurement with ORA using the WS ≥6 as quality index achieved high inter-examiner reproducibility for all ORA parameters. High reproducibility was obtained even by inexperienced examiners when considering the mean of the best 3 measurements per eye.
Abstract: Low intraocular pressure (IOP) measured by Goldmann applanation tonometry (GAT) is one of the ocular manifestations of Steinert's myotonic dystrophy. The goal of this study was to evaluate the corneal-compensated IOP as well as corneal properties (central corneal thickness and corneal hysteresis) in patients with myotonic dystrophy.
Abstract: To evaluate corneal biomechanics with the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Depew, NY) after penetrating keratoplasty (PK) and deep anterior lamellar keratoplasty (DALK).
Abstract: To compare measurements obtained by Goldmann applanation tonometry (GAT) and Pascal dynamic contour tonometry (DCT), and to study their relationship to corneal thickness and biomechanical properties in nonglaucomatous eyes.
Abstract: Purpose. To evaluate the Goldmann applanation tonometer (GAT), the Pascal dynamic contour tonometer (PDCT), and the ocular response analyzer (ORA) tonometer in measuring intraocular pressure (IOP) in keratoconic eyes before and after riboflavin/ultraviolet A corneal collagen crosslinking (CXL), to assess agreement among devices and to analyze the impact of some ocular parameters on their measurements. Methods. Fifty keratoconic eyes were included. Intraocular pressure was measured with GAT, PDCT, and ORA before and after CXL. Fifty nonkeratoconic eyes served as controls. Device agreements were calculated by Bland-Altman analysis. The effect of some ocular characteristics on IOP measurement differences between tonometers was determined. Results. Between the 2 groups, there were statistically significant differences in all examined parameters. Preoperatively, in both groups a statistically significant difference was found in IOP measurements among devices (p<0.05). Bland-Altman analysis showed a bias among devices. On average, PDCT overread GAT and ORA. The IOP measurement differences were better predicted by corneal resistance factor. Postoperatively, in keratoconus eyes, there was no statistically significant difference in IOP measurements among the 3 tonometers (p>0.05). The IOP readings with all tonometers after treatment were higher than those obtained preoperatively; however, not to a statistically significant level, with the exception of PDCT and ORA readings at the first month postoperatively. Corneal resistance factor measurements have no significant change after CXL. Conclusions. Pascal dynamic contour tonometer could provide more consistent and closer to the true IOP readings than GAT and ORA in healthy eyes with corneal thickness outside the 520-550 µm range, in keratoconus patients and after CXL. Corneal resistance factor was associated significantly with agreement among devices.
Abstract: To compare biomechanical properties of transplanted corneas after penetrating keratoplasty (PK) with those after deep anterior lamellar keratoplasty (DALK) using Anwar's big-bubble technique.
Abstract: PUPOSE: The purpose of this study was to compare the biomechanical properties of the cornea and intraocular pressure (IOP) between patients with systemic lupus erythematosis (SLE) and age-matched controls.
Abstract: We report a case of melanoma-associated retinopathy (MAR) associated with positive auto-antibodies against retinal bipolar cells, which has been rarely reported in Japan.
Abstract: This study aims to investigate the effect of both flap creation and laser ablation on corneal hysteresis (CH) and corneal resistance factor (CRF), as well as the inward applanation signal amplitude produced by the ocular response analyzer (ORA), immediately following each step of the LASIK procedure using the Intralase femtosecond laser for flap creation.
Abstract: PURPOSE:: To assess the biomechanical properties of corneas in patients with normal tension glaucoma (NTG) and to compare them with those of patients with primary open-angle glaucoma (POAG), ocular hypertension (OHT), and normal controls (N). METHODS:: Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann intraocular pressure (IOPg), and corneal compensated IOP (IOPcc) were obtained using an ocular response analyzer for 28 eyes in 14 patients with NTG, 75 eyes in 38 patients with chronic POAG, 53 eyes of 27 patients with OHT, and 44 eyes of 22 N controls. IOP using Goldmann applanation tonometry (IOPGA) and ultrasonic central corneal thickness (CCT) were also measured for each eye. Analysis of variance test was used for statistical analysis. RESULTS:: CH was significantly lower in the NTG group (9.88±2.02 mm Hg) compared with the N group (11.05±1.53 mm Hg; P<0.01). CRF was significantly lower in the NTG group (9.5±1.89 mm Hg) compared with the POAG group (11.15±2.35 mm Hg; P<0.01) and to the N group (11.00±1.75 mm Hg; P<0.01). CCT was not considered significantly different between the 4 groups. However, IOPcc was found to be significantly lower in NTG group compared with the POAG group and OHT group (P<0.001). CONCLUSION:: NTG was associated with significantly lower CRF than chronic POAG and N patients. CH and CRF could be a useful tool in early diagnosis of NTG.
Abstract: PURPOSE: To evaluate the repeatability and interoperator reproducibility of the Pascal dynamic contour tonometry (DCT), ocular response analyzer (ORA), and Goldmann applanation tonometer (GAT) in a single population of normal individuals. METHODS: The study included 52 eyes from 26 normal individuals. One operator measured the intraocular pressure (IOP) with each tonometer 3 times while 2 additional operators each measured the IOP with each tonometer once. Repeatability and reproducibility were assessed by the coefficient of variation (CV) and intraclass correlation coefficient (ICC). Agreement among tonometers was also assessed using Bland-Altman plots. RESULTS: The mean age of included participants was 31.5±8.8 years and 15 (58%) were female individuals. In general, both intraoperator repeatability and interoperator reproducibility were significantly higher for DCT compared with the other tonometers. Intraoperator DCT (CV=3.7, ICC=0.89), GAT (CV=9.7, ICC=0.79), IOPg (CV=7.0, ICC=0.79), and IOPcc (CV=9.8, ICC=0.57). Interoperator DCT (CV=6.1, ICC=0.73), GAT (CV=9.0, ICC=0.82), and IOPg (CV=10.8, ICC=0.63), IOPcc (CV=11.7, ICC=0.49). CONCLUSION: Overall, DCT was significantly more repeatable and reproducible than GAT, IOPg and IOPcc. The better reproducibility of the DCT may result in more precise measurements for monitoring IOP changes over time compared to GAT and ORA.
Abstract: Monochromatic aberrations may influence the visual acuity of the eye. They are not stable and can be affected by different factors. The subject of the following paper is the dynamic investigation of the changes in wavefront aberration with accommodation.
Abstract: To determine the agreement between dynamic contour tonometer (DCT), Goldmann applanation tonometer (GAT), and Ocular Response Analyzer (ORA) in keratoconic corneas and to find out the effect of corneal biomechanics on intraocular pressure (IOP) measurements obtained by these devices.
Abstract: To compare corneal hysteresis (CH), corneal resistance factor (CRF), spherical equivalent (SE), average central keratometry (K-Avg), corneal astigmatism (CA), corneal volume (CV), anterior chamber (AC) depth, and central corneal thickness (CCT) between patients with mild keratoconus and healthy controls and to estimate the sensitivity and specificity of CH and CRF in discriminating mild keratoconus from healthy corneas.
Abstract: PURPOSE.: To study the usefulness of the Waveform Score from the ocular response analyzer (ORA). METHODS.: Both eyes of sixty-four normal Chinese adults were measured by the ORA. An experienced practitioner who was masked to the score evaluated the waveforms. Four measurements were obtained from each eye, and the average was considered as the gold standard. Agreement was compared for the mean of different multiple measurements to the gold standard. RESULTS.: There was no significant difference between the gold standard and the mean of different multiple measurements for all ORA parameters. The Waveform Score of 512 signals (four measurements from each eye of 64 subjects) ranged from 1.58 to 9.06. When the best signal value of four measured signals from each eye was considered, the lowest score was 3.60 from 128 eyes. The lower 10th percentile from all signals had Waveform Scores <3.48. CONCLUSIONS.: If the Waveform Score provides information on the reliability of the signals, a score <3.50 may indicate an unreliable signal, and the signal should be discarded. We also recommend taking three measurements with all the signals having a Waveform Score of 3.50 or above to increase the precision.
Abstract: To examine the repeatability and reproducibility of intraocular pressure (IOP) measurements obtained with the Goldmann applanation tonometer (GAT), the Pascal dynamic contour tonometer (DCT; Swiss Microtechnology AG, Port, Switzerland), and the Reichert Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY). A secondary objective was to assess agreement between the devices.
Abstract: Among the various intraocular pressure (IOP) measurement methods available today, Goldmann applanation tonometry (GAT) remains the gold standard for in-office routine IOP measurement. However, numerous factors may affect IOP measurement with GAT, namely corneal features. Before any interpretation of an IOP value, the measurement conditions should be checked and the central corneal thickness evaluated, since GAT overestimates IOP in thick corneas and underestimates IOP in thin ones. When GAT is not applicable, other IOP measurement devices, which have their own limits, are available. For example, the ocular response analyzer (ORA) and dynamic contour tonometry (DCT) provide IOP readings that are less influenced by corneal properties and may be useful after refractive surgery. Regardless of the choice of tonometer, the IOP value must not be considered alone but from a clinical point of view, including, namely, multiple IOP measurements over a day since the IOP fluctuates over a 24-h time period. A complete clinical examination is necessary in each case to search for glaucomatous neuropathy.
Abstract: To investigate corneal viscoelasticity in primary open-angle glaucoma patients with and without diabetes mellitus, and to correlate corneal hysteresis (CH) with central corneal thickness (CCT).
Abstract: To compare preoperative and postoperative measurements of corneal biomechanical properties and intraocular pressure (IOP) using Goldmann applanation tonometry (GAT) and the ocular response analyzer (ORA) in eyes undergoing deep sclerectomy with collagen implant (DSCI).
Abstract: To evaluate whether postural changes of intraocular pressure (IOP) are associated with visual field damage by comparing both eyes of patients with previously untreated normal-tension glaucoma (NTG).
Abstract: For many years researchers have discussed which corneal parameters can influence the measurement of intraocular pressure (IOP). As a substantial parameter, the central corneal thickness (CCT) is assumed; however, different measuring methods - including Goldmann applanation tonometry (GAT), dynamic contour tonometry (DCT), and corneal compensated pressure measured with the ocular response analyzer (IOPcc) - may lead to a completely different dependence on corneal thickness.
Abstract: To investigate intraocular pressure (IOP) measurement values in normal tension glaucoma (NTG) eyes using two different types of tonometer that are supposed to be little affected by corneal biochemical properties.
Abstract: To assess the effect of corneal astigmatism on intraocular pressure (IOP) measurements using an Ocular Response Analyzer (ORA) and a Goldmann applanation tonometer (GAT).
Abstract: To propose a new approach for the study of corneal biomechanics using the Reichert Ocular Response Analyzer (ORA) database, which is based on changes in velocity retardation in the central cornea at the peak of flattening.
Abstract: The authors estimated the association between corneal biomechanical properties and axial length in myopic children and verified the relationship between axial length and intraocular pressure (IOP).
Abstract: To investigate the relationship between corneal biomechanical properties and confocal microscopy (CM) findings in normal and keratoconic eyes.
Abstract: To compare the corneal biomechanical properties in eyes of patients with diabetes mellitus and in those of subjects without diabetes mellitus.
Abstract: Comparison of the magnitude and repeatability of the intraocular pressure (IOP) measured with the Ocular Response Analyzer (ORA) to that measured with the Goldmann tonometer.
Abstract: To investigate the association between corneal biomechanical parameters and asymmetric primary open angle glaucoma (POAG) using the Ocular Response Analyzer (ORA).
Abstract: To compare intraocular pressure (IOP) measurements obtained with the Goldmann applanation tonometer (GAT) and the ocular response analyzer (ORA) in patients with keratoconus (KC) and analyze their dependence on ocular anatomic parameters.
Abstract: The purpose of this study was to evaluate some of the methods used to calculate objective refractions from wavefront aberrations, to determine their applicability for accommodation research. A wavefront analyzer was used to measure the ocular aberrations of 13 emmetropes and 17 myopes at distance, and 4 near target vergences: 2, 3, 4, and 5 D. The accommodative response was calculated using the following techniques: least squares fitting (Zernike defocus), paraxial curvature matching (Seidel defocus), and 5 optical quality metrics (PFWc, PFSc, PFCc, NS, and VSMTF). We also evaluated a task-specific method of determining optimum focus that used a through-focus procedure to select the image that best optimized both contrast amplitude and gradient (CAG). Neither Zernike nor Seidel defocus appears to be the best method for determining the accommodative response from wavefront aberrations. When the eye has negative spherical aberration, Zernike defocus tends to underestimate, whereas Seidel defocus tends to overestimate the accommodative response. A better approach is to first determine the best image plane using a suitable optical quality metric and then calculate the accommodative error relative to this plane. Of the metrics evaluated, both NS and VSMTF were reasonable choices, with the CAG algorithm being a less preferred alternate.
Abstract: To evaluate the sensitivity, specificity, and test accuracy of corneal biomechanical metrics and anterior segment data in differentiating keratoconus from healthy corneas.
Abstract: To compare 2 corneal biomechanical parameters--corneal hysteresis (CH) and corneal resistance factor (CRF)--before and after collagen crosslinking (CXL) for keratoconus.
Abstract: To examine the biomechanical properties of keratoconic eyes following penetrating keratoplasty and to compare results with the biomechanical characteristics of manifest keratoconus, forme fruste keratoconus and normal eyes as measured with the Reichert ocular response analyzer (ORA).
Abstract: To analyze and compare corneal biomechanical properties in healthy black and white subjects using the Ocular Response Analyzer (ORA) and to evaluate their relationship with other ocular parameters.
Abstract: The aim of this study was to compare the intra-ocular pressure (IOP) obtained by ocular response analyzer (ORA), dynamic contour tonometer (DCT) and Goldmann applanation tonometer (GAT). In 102 patients (47 with primary open-angle glaucoma and 55 healthy controls) IOP was measured with GAT, ORA and DCT in one eye. The agreement between GAT, DCT and ORA values was assessed using Bland-Altman plots. The discrepancy between the methods was related to central corneal thickness (CCT), corneal hysteresis (CH) and corneal resistance factor (CRF) using linear regression models. Significant differences were observed amongst DCT, corneal compensated ORA (ORAcc) and GAT (P < 0.01). Only the ORAcc and DCT were comparable. ORAcc and DCT significantly over-estimated IOP compared to GAT and for ORAcc this difference depended on the height of IOP. A significant correlation was found between CCT and the deviation of DCT and ORAcc from corrected GAT (both P < 0.0001). Our study showed a low degree of agreement between IOP measured by ORA, DCT and GAT. DCT and ORAcc over-estimated the IOP compared to GAT.
Abstract: The Reichert ocular response analyzer (ORA) measures corneal biomechanical properties in vivo by monitoring and analyzing the corneal behavior when its structure is submitted to a force induced by an air jet. This study was designed to examine corneal biomechanical properties and intraocular pressure in patients with systemic sclerosis (SSc) and to compare with control eyes.
Abstract: To compare changes in corneal hysteresis (CH) and the corneal resistance factor (CRF) in myopic and hyperopic laser in situ keratomileusis (LASIK) and evaluate their relationship to the number of photoablative pulses delivered, a surrogate for ablation volume.
Abstract: To determine the factors affecting corneal biomechanics using biomechanical waveform analysis after microincision cataract surgery (MICS) and standard coaxial phacoemulsification with different incision sizes.
Abstract: To test the hypothesis that patients with keratoconus and pellucid who have glaucoma or are glaucoma suspects have lower corneal hysteresis (CH) and/or corneal resistance factor (CRF) measurements compared with controls.
Abstract: To report a case of progressive corneal ectasia after LASIK with no detectable preoperative risk factors and to present three-dimensional corneal tomographic and biomechanical findings on the contralateral unoperated eye that would be considered low risk for ectasia and thereby a good LASIK candidate based on the Randleman Ectasia Risk Score System (ERSS).
Abstract: To evaluate corneal biomechanical properties in eyes that had previously undergone penetrating keratoplasty (PK) using the ocular response analyzer (ORA).
Abstract: To analyze the effect of using one reading, the mean of two readings (from the same eye), or the mean of four readings (two from each eye) on the heritability estimates of intraocular pressure (IOP). This was a cohort study in which 344 pairs of twins, 163 monozygotic (MZ) and 181 dizygotic (DZ), were enrolled.
Abstract: To investigate possible corneal biomechanical changes in patients with diabetes mellitus and understand the influence of such changes on intraocular pressure measurements.
Abstract: To establish the literature basis that could support the idea that it would be possible to analyze changes at the anterior surface of the cornea induced by an air jet applied onto the eye.
Abstract: To examine the relationship between office-hour changes in IOP, measured with the Goldmann applanation tonometer (GAT) and dynamic contour tonometer (DCT), and the corneal characteristics central corneal thickness (CCT) and corneal hysteresis (CH).
Abstract: Differences in corneal viscoelasticity due to diabetes have been reported to have a protective effect on the progression of glaucoma and the development and progression of keratoconus. Due to longterm changes of tissue in diabetes mellitus, biomechanical changes of the cornea because of glycation and modified extracellular matrix may be detectable. The purpose of the study was to determine whether there is a difference in corneal biomechanical properties, characterized by corneal hysteresis (CH) and central corneal thickness (CCT), between diabetic and normal subjects, and relate these to the duration of diabetes.
Abstract: To assess changes in biomechanical properties of human cornea after treatment of keratoconus with UV-A-riboflavin corneal collagen cross-linking (CXL).
Abstract: Several methods permit the measurement of geometric parameters of the cornea, but until now biomechanical conditions of the cornea have been ignored (e.g. in refractive corneal surgery). Besides the geometric condition, biomechanical properties of the cornea have been shown to influence applanation measurement of intra-ocular pressure (IOP) and epidemiological studies have identified corneal thickness as an independent risk factor for the development and progression of glaucoma. The aim of this investigation was to characterize the biomechanical properties of the cornea using the ocular response analyzer (ORA).
Abstract: To investigate the topical use of travoprost [Trademark: Travatan (Alcon laboratories Inc, TX)] and the incidence of iridial pigmentation change in the brown irises of Chinese eyes.
Abstract: To compare intraocular pressure (IOP) between patients with myotonic dystrophy (DM1) and normal subjects, taking into account corneal characteristics. To determine whether lower IOP measurements in patients with DM1 are due to thinner corneas.
Abstract: To investigate the effects of Fuchs' corneal dystrophy (FCD) on corneal biomechanical properties and the results of IOP readings in relation to changes in corneal hysteresis (CH) and central corneal thickness (CCT).
Abstract: To compare parameters of biomechanical response of the human cornea measured as corneal hysteresis (CH) and corneal resistance factor (CRF) in patients with diabetes mellitus and healthy control subjects.
Abstract: To measure corneal hysteresis (CH) in unilateral chronic primary angle-closure glaucoma (CPACG) patients to determine if it was affected by high intraocular pressure (IOP).
Abstract: To assess corneal biomechanical changes in eyes undergoing phototherapeutic keratectomy (PTK) and to investigate the relationship of PTK with corneal thickness.
Abstract: Transparency of ocular media enables the precise quantitative analysis of vessels of retina, a neuronal tissue which can be affected by multiple sclerosis (MS).
Abstract: To compare the postoperative biomechanical properties of the cornea after photorefractive keratectomy (PRK) and after laser in situ keratomileusis (LASIK) in eyes with myopia.
Abstract: To assess the agreement among ocular response analyzer (ORA), dynamic contour tonometry (DCT), Goldmann applanation tonometry (GAT), and noncontact tonometry (NCT), and to determine the effects of central corneal thickness (CCT) and corneal hysteresis (CH) on intraocular pressure (IOP) measurements with these devices.
Abstract: The aim of the present study was to evaluate the clinical usefulness of riboflavin- and ultraviolet-A (UV-A)-induced collagen cross-linking (CXL) on progressive keratoconus.
Abstract: To compare the corneal hysteresis (CH) and corneal resistance factor (CRF) measured with the Ocular Response Analyzer (ORA) in normal and keratoconic eyes.
Abstract: To test the hypothesis that keratoconus and pellucid patients who have glaucoma or are suspected of having glaucoma have lower corneal hysteresis (CH) and/or corneal resistance factor (CRF) measurements compared to controls.
Abstract: To compare the intraocular pressure (IOP) readings taken by ICare, Pascal dynamic contour tonometer (DCT), and ocular response analyzer (ORA) with those taken by Goldmann applanation tonometer (GAT). We sought to evaluate the influence of central corneal thickness (CCT) on IOP measurements and to compare patients' preferences for the four tonometers.
Abstract: The study was undertaken to determine the parameters of corneal hysteresis in healthy individuals and patients before and after non-automated endokeratoplasty. An Ocular Response Analyzer (Reichert Inc., USA) was used to study ocular biochemical properties. At the same time, the value of corneal hysteresis (mm Hg) and the central corneal thickness (microm) were evaluated. The study demonstrated lower corneal hysteresis in primary and secondary corneal dystrophy than that in normal eyes.
Abstract: To compare intraocular pressure (IOP) and corneal biomechanical metric changes after myopic laser in situ keratomileusis and laser-assisted subepithelial keratectomy (LASEK).
Abstract: The ocular response analyzer (ORA) is a new indentation tonometer that subjects the cornea to an increasing then decreasing air pulse, and uses the corresponding two applanation pressures P1 and P2 to estimate the intraocular pressure (IOP). The present study aims to improve the accuracy of IOP estimation through representative numerical simulation of the ORA procedure. A parametric study has been carried out to consider the effect of corneal thickness, curvature, age, and true IOP on the P1 and P2 measurements. Based on the obtained database of input and output parameters, an equation has been suggested relating the P1 and P2 measurements to the value of IOP. The equation is intended to make IOP estimates independent of corneal stiffness, which varies with size and age. The equation has been tested against a clinical data set obtained at Moorfields Eye Hospital involving 144 subjects, and found to produce IOP estimates that are less dependent on corneal size and age than published equations.
Abstract: Tonometry is the measurement of intraocular pressure (IOP). Normal IOP values range from 10 to 21 mmHg (15.5 mmHg+/-2 SD). They are influenced by various factors, including the patient's position during measurement, central corneal thickness, corneal diameter and curvature, rigidity of the cornea, and the cornea's state of hydration. Until now, Goldmann applanation tonometry has been seen as the gold standard for intraocular pressure measurement. But many new techniques and devices for determining IOP have been developed, such as noncontact tonometry, the Tono-Pen, the ICare tonometer, dynamic contour tonometry, TGDc-01 tonometry, and the ocular response analyzer. The aim of these techniques is to minimize distorting influences to obtain the "true IOP." Several of these methods show advantages in specific situations; however, limitations exist that should be considered when interpreting the obtained IOP results. This article describes the individual methods of measurement and discusses their advantages and disadvantages.
Abstract: The aim of this study was to investigate the biomechanical properties of the cornea and their association with intraocular pressure (IOP), central corneal thickness (CCT) and the central corneal radius of curvature (Rc).
Abstract: To evaluate the biomechanical and morphological changes in keratoconic corneas after Intacs intrastromal corneal ring segment (ICRS) implantation.
Abstract: The ocular response analyzer (ORA) uses an air-pressure-triggered, dynamic, bi-directional corneal applanation method to measure biomechanical parameters of the cornea. Corneal hysteresis (CH) is defined as the difference in intraocular pressure recorded during inward and outward applanation. CH is therefore an indicator for the viscoelastic properties of the cornea.
Abstract: To analyze the correlation between corneal hysteresis (CH) measured with the Ocular Response Analyzer (ORA, Reichert) and ultrasonic corneal central thickness (CCT US) and intraocular pressure measured with Goldmann applanation tonometry (IOP GA).
Abstract: To determine the efficacy of the Reichert Ocular Response Analyzer (ORA) to measure intraocular pressure (IOP) following corneal laser refractive surgery.
Abstract: Goldmann applanation tonometry (GAT) has been the gold standard for measuring intraocular pressure (IOP) for about 50 years. However, it depends on central corneal thickness (CCT) and is, therefore, prone to being incorrect. Dynamic contour tonometry (DCT) has recently been introduced to measure IOP independently of CCT; however, DCT is costly and difficult. IOP measurement using the ocular response analyzer (ORA) offers noncontact tonometry with declaration of the corneal-compensated IOP (IOPcc), which takes corneal hysteresis (CH) into account and is supposed to be independent of CCT.
Abstract: To examine the roles of genetic and environmental factors in corneal hysteresis and ocular pulse amplitude by performing a classic twin study.
Abstract: To study the short-term corneal response to corneal refractive therapy for myopia and correlate it with corneal biomechanical properties as measured with the ocular response analyzer.
Abstract: Acquired pit-like changes of the optic nerve head (APON) are characteristic of glaucomatous damage and may be a sign of a localized susceptibility of the optic nerve. Thus, it is possible that biomechanical properties of the ocular tissues may play a pressure-independent role in the pathogenesis of glaucoma. Corneal hysteresis (CH) appears to provide information of the biomechanical properties of the ocular hull tissues. The purpose of this study was to compare CH of patients with primary open angle glaucoma (POAG) with and without APON.
Abstract: To determine the influence of corneal thickness, corneal hysteresis (CH), and corneal resistance factor (CRF) on intraocular pressure (IOP) measurements obtained using the iCARE rebound tonometer.
Abstract: A precise assessment of the intraocular pressure (IOP) is crucial for diagnosis and decision making regarding treatment modalities in patients with glaucoma. Recent epidemiologic studies show that a difference of only 1 mm Hg in the mean IOP may be critical enough to determine the visual field prognosis in patients with glaucoma. However, the Goldmann applanation tonometer, which is current gold standard, is not precise enough to measure the true IOP within an error of 1 mm Hg. There are many clinically proposed correction algorithms to correctly measure IOP. However, corrections using only the central corneal thickness and curvature may not be sufficient in each individual case. In this article, previously reported theoretical equations about the effects of corneal topography, modulus of elasticity, and tear film on Goldmann applanation tonometric IOP readings were reviewed, and their discrepancies with clinical or experimental data were analyzed. Thereafter, new tonometers such as the dynamic contour tonometer, the rebound tonometer, and the ocular response analyzer were compared with the Goldmann applanation tonometer and other popular tonometers.
Abstract: To explain the basic science and clinical evidence that has led to the development of a new technique in corneal refractive surgery--sub-Bowman's keratomileusis (SBK).
Abstract: The ocular response analyzer (ORA) (Reichert, Inc.) was used in the case of a middle-aged man who developed unilateral corneal ectasia after bilateral laser in situ keratomileusis (LASIK). The preoperative refraction was similar in the 2 eyes. Post-LASIK ectasia was central in the left eye; topography was oblate in the right eye. The ORA values consisted of the mean of 4 measurements. Corneal hysteresis and corneal resistance factor were almost equal in the ectatic eye and the nonectatic eye. However, significant between-eye differences in the morphology of the signals were noted, most prominently in the lower amplitude of the applanation peaks in the ectatic eye. The shape of the applanation signal yielded important information in addition to corneal hysteresis and corneal resistance factor.
Abstract: To investigate relationships between acute intraocular pressure (IOP)-induced optic nerve head surface deformation and corneal hysteresis and thickness in glaucomatous and nonglaucomatous human eyes.
Abstract: In the last 10 years, several new means to measure intraocular pressure have emerged. This review covers recent findings concerning four new technologies: the ocular response analyzer, dynamic contour tonometry, rebound tonometry and the Proview phosphene tonometer.
Abstract: To assess the reproducibility of the ocular response analyzer (ORA) in nonoperated eyes and the impact of corneal biomechanical properties on intraocular pressure (IOP) measurements in normal and glaucomatous eyes.
Abstract: The aim of this study was to investigate the corneal hysteresis (CH) and corneal resistance factor (CRF) in normal eyes and to determine their relationship between central corneal thickness (CCT), corneal curvature, sphere equivalence (SE) and intraocular pressure (IOP).
Abstract: To investigate, in healthy Asian subjects, the diurnal changes of the corneal biomechanical properties of corneal hysteresis (CH) and its relation to fluctuations of intraocular pressure (IOP) and central corneal thickness (CCT) after sleeping.
Abstract: To evaluate corneal viscoelastic and intraocular pressure (IOP) changes measured by an ocular response analyzer (ORA) after phacoemulsification and intraocular lens (IOL) implantation.
Abstract: (1) Evaluate and analyze the Ocular Response Analyzer (ORA) in three groups of patients: glaucoma, intraocular hypertension, and normal; (2) study corneal hysteresis values in the three groups according to age; and (3) compare intraocular pressure values measured with the ORA with intraocular pressure measured with Goldmann (IOPGoldmann) and pulsed air (IOPair) applanations.
Abstract: The Ocular Response Analyzer (ORA) measures corneal biomechanical properties: corneal hysteresis (CH) and the corneal resistance factor (CRF). The Pascal Dynamic Contour Tonometer (PDCT) measures the ocular pulse amplitude (OPA), which represents the systolic-diastolic variation in intraocular pressure (IOP). Both ORA and OPA values are lower in glaucoma patients than in normal patients. Our purpose was to assess whether there is a correlation between CH, CRF, and OPA values in healthy subjects.
Abstract: To evaluate the intraoffice hour variability of intraocular pressure (IOP) and in vivo biomechanical properties of the cornea, as measured with the Ocular Response Analyzer (ORA).
Abstract: To study the correlation between corneal biomechanical properties and surgical parameters in myopic patients before and after laser in situ keratomileusis (LASIK).
Abstract: To determine and compare the corneal biomechanical properties between eyes with primary open angle glaucoma (POAG) and eyes with normal tension glaucoma (NTG).
Abstract: The Ocular Response Analyzer (ORA) is a newly introduced tonometer that uniquely measures and then integrates corneal biomechanical data into its intraocular pressure (IOP) estimates in an effort to improve accuracy of IOP assessment. This study was devised to investigate whether ORA-derived IOP and corneal biomechanical variables might be useful in discriminating between subjects with and without primary open-angle glaucoma (GLC).
Abstract: The dynamic contour tonometer (DCT; Pascal tonometer) and the Ocular Response Analyzer (ORA) are novel tonometers designed to measure intraocular pressure (IOP) independent of corneal properties and central corneal thickness (CCT), respectively. We wanted to compare the corneal compensated IOP (IOPcc) as measured by ORA with IOP values measured by DCT and Goldmann applanation tonometry (GAT) with respect to IOP readings and the influence of corneal hysteresis (CH) and CCT in glaucoma patients.
Abstract: The influence of central corneal thickness (CCT) on the measurement of intraocular pressure (IOP) has been discussed extensively in recent years. The problem, however, has not been solved so far. In addition to CCT there are probably further biomechanical properties that play a role in IOP measurement. We wanted to find out whether these properties are related to Goldmann applanation tonometry (GAT), noncontact tonometry (NCT), or CCT.
Abstract: To compare the preoperative and postoperative measurement of corneal biomechanical properties and intraocular pressure (IOP) using Goldmann applanation tonometry (GAT), the ocular response analyzer (ORA), and the Pascal dynamic contour tonometer (PDCT) in eyes undergoing myopic laser in situ keratomileusis (LASIK).
Abstract: To determine if corneal hysteresis (CH) was associated with increased central corneal thickness (CCT) induced by wearing soft contact lenses during eye closure.
Abstract: To compare intraocular pressure (IOP) obtained from the ocular response analyzer (ORA) and Goldmann applanation tonometer (GAT) on a group of normal Chinese.
Abstract: In many arthropod eyes the ommatidia contain two classes of retinular cells with orthogonally oriented microvilli. These receptors provide the basis for two-channel polarization vision. In several contexts such as navigation or the detection of polarization contrast, two channels may be insufficient. While solutions to this problem are known (e.g. in insects and stomatopod crustaceans) none have been found in the majority of decapods. To examine this issue further, the polarization sensitivity and the E-vector angle eliciting a maximum response (theta (max)) were measured at over 300 loci on the crayfish retinula. The polarization response ratio (which is proportional to polarization sensitivity) was similar at all locations on the retinula. Around the central pole of the eye, theta (max) was distributed about the vertical and horizontal axes. Along the dorsal rim, the distribution of theta (max) exhibits modes at 0 degrees , 45 degrees and 90 degrees and a small mode at 135 degrees relative to the dorso-ventral axis of the eyestalk (0 degrees ). Smaller numbers of cells (20 to 25%) with theta (max )near the diagonal were also found in anterior and posterior retinula areas. Thus crayfish visual interneurons, which integrate signals from multiple ommatidia may have access to a multi-channel polarization analyzer.
Abstract: To evaluate the accuracy of ocular response analyzer (ORA) parameters (corneal hysteresis (CH), corneal resistance factor (CRF), and ocular tension (IOPcc and IOPg)) and the correlation with corneal biometry measured with the Orbscan topographer.
Abstract: To estimate the relationships between ocular parameters and tonometrically measured intraocular pressure (IOP), to determine the influence of ocular parameters on different instrument measurements of IOP, and to evaluate the association of ocular parameters with a parameter called hysteresis.
Abstract: To compare the biomechanical properties of normal, post-laser in situ keratomileusis (LASIK), and keratoconic corneas evaluated by corneal hysteresis and the corneal resistance factor measured with the Reichert Ocular Response Analyzer (ORA).
Abstract: To assess the changes in corneal hysteresis (CH) as measured by the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, New York, USA) to describe the influence of clear corneal cataract surgery on corneal viscoelastic properties and intraocular pressure (IOP) measured by noncontact tonometry (NCT) and Goldmann applanation tonometry (GAT).
Abstract: Central corneal thickness has become an important biometric factor and is an essential part of the evaluation of glaucoma. Goldmann applanation tonometry is the most widely used method of measuring intraocular pressure, but it is well known that corneal parameters affect the accuracy of this instrument. Intraocular pressure reduction is currently the only treatment available for decreasing the risk of glaucoma progression, so it is important to have an accurate reading of the true intraocular pressure.
Abstract: We sought to measure the impact of central corneal thickness (CCT), a possible risk factor for glaucoma damage, and corneal hysteresis, a proposed measure of corneal resistance to deformation, on various indicators of glaucoma damage.
Abstract: The Ocular Response Analyzer (ORA) proposes to measure corneal biomechanical properties in vivo by monitoring and analyzing the corneal behavior when this structure is submitted to a force induced by an air jet. The purpose of this study was to evaluate the relationship between corneal biomechanical properties and corneal-compensated intraocular pressure (IOPCC) measurements as obtained by the ORA and Goldmann applanation tonometry (GAT) measurements.
Abstract: To examine corneal hysteresis in children with normal eyes and congenital glaucoma and assess intraocular pressure (IOP) measurement with the Reichert Ocular Response Analyzer (RORA).
Abstract: To establish correlations between intraocular pressure (IOP) measurements obtained with the ocular response analyzer (ORA) and the Goldmann applanation tonometer (GAT). The effects of central corneal thickness on the measures obtained were also examined.
Abstract: The Ocular Response Analyzer (ORA) is a new instrument that measures the corneal biomechanical response (corneal hysteresis, CH) to rapid indentation by an air jet. CH is the difference in applanation pressures (P1, P2) between the rising and falling phases of the air jet. The investigation had two parts: a characterization study and a validation study. In the characterization study, the purposes were to investigate the intraocular pressure (IOP)-dependence of CH and to characterize the performance of the ORA. In the validation study, the purposes were to investigate the association between CH and both age and central corneal thickness (CCT) and the agreement between ORA and Goldmann applanation tonometer (GAT) IOP measurements.
Abstract: To study the results of an ocular response analyzer (ORA) to determine the biomechanical properties of the cornea and their relationship to intraocular pressure (IOP).
