PurposeTo evaluate and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in pellucid marginal degeneration (PMD), keratoconus (KCN), and normal eyes using the Ocular Response Analyzer (ORA).MethodsIn this retrospective study, corneal biomechanical parameters were measured in patients with PMD (n = 102) and KCN (n = 202) and normal subjects (n = 208) using the ORA. Data, including full patient history as well as the results of refraction, slit-lamp biomicroscopy, Pentacam HR (Oculus), and ORA (Reichert; Buffalo, New York, USA), were collected from medical records. Also, the data of only one eye per individual were selected for the analysis. The inclusion criteria for PMD and KCN groups were a reliable diagnosis of these ectatic disorders based on the clinical and corneal tomographic findings. CH, CRF, CH–CRF, intraocular pressure (IOP) measurements were assessed for each subject. Data were analyzed with SPSS and MedCalc using the ANOVA, Pearson Correlation, and receiver operating characteristic (ROC) curve analysis.ResultsThe mean CH was 8.91 mmHg ± 1.05 [standard deviation (SD)], 8.43 ± 0.78, and 10.89 ± 1.08 in the PMD, KCN, and normal group, respectively. Also, the mean CRF was 8.21 ± 1.35, 7.19 ± 1.11, and 10.69 ± 1.41 in the PMD, KCN, and normal group, respectively. ANOVA showed differences in the mean CH, CRF, and CH–CRF between three groups (P < 0.001). Also, ROC curve analysis showed the cut-off points ≤9.5, ≤9.5, and >1.3 mmHg for CH, CRF, and CH–CRF in the PMD group, respectively. For biomechanical parameters in PMD eyes, CRF had the highest sensitivity (75.49%) while the greatest area under the ROC curve (AUC) was seen for CH (0.903). Moreover, central corneal thickness (CCT) showed no correlation with CH (P = 0.30, r = −0.104) or CRF (P = 0.75, r = 0.033) in the PMD group.ConclusionsThis study presented the values of corneal biomechanics for PMD using the ORA. The results of the ORA were markedly different between PMD, KCN, and normal eyes.

PurposeThe aim of this study was to evaluate and compare tomographic and biometric characteristics measured by the corneal tomography and ocular biometry in bilateral keratoconus (KCN) patients with and without corneal Vogt’s striae.MethodsNinety-two eyes of 46 subjects with a reliable diagnosis of bilateral KCN with unilateral Vogt’s striae were enrolled in this cross-sectional contralateral eye study. In addition to refraction (calculated by vectorial analysis) and visual acuity, corneal tomographic measurements were obtained by the Pentacam (Scheimpflug-based anterior segment tomography). Also, ocular biometric characteristics were evaluated using the Ocuscan® RxP (ultrasound biometer). The KCN eyes were categorized into two groups, including eyes with Vogt’s striae and eyes without Vogt’s striae.ResultsOur results showed significant differences in the sphere, cylinder, spherical equivalent, J0, corrected and uncorrected distance visual acuity, flat, steep and maximum keratometry, anterior chamber depth (ACD), and central corneal thickness (CCT) between the two groups (all P<0.001). The eyes without Vogt’s striae had a shorter ACD measured by the Pentacam and biometer. There were no differences in axial length (AL) and vitreous length (VL) between the two groups (all P>0.05). Also, there was poor agreement between the measurements of the Pentacam and ultrasound biometer for ACD in the study groups.ConclusionCorneal tomographic and ocular biometric measurements showed significant differences between KCN eyes with and without Vogt’s striae except for AL and VL. These differences should be noticed in clinical evaluations and treatment of KCN patients.