Corneal biomechanics in different age groups.

PURPOSE: To report on the corneal biomechanical characteristics, namely the corneal hysteresis (CH), corneal resistance factor (CRF), as well as the intraocular pressure (IOP) goldman compensated (IOPg), and the cornea compensated (IOPcc), using the ocular response analyzer (ORA) in different age groups in a cohort of normal individuals from the second decade to the seventh decade and beyond. PATIENTS AND METHODS: The study was a cross-sectional survey conducted on 997 eyes of 508 normal individuals presenting for a routine ophthalmic examination at Alexandria Main University Hospital in Alexandria University, Alexandria, Egypt. The study subjects were age stratified into decades (10-20, 21-30, 31-40, 41-50, > 50) and the ORA parameters (CH, CRF, IOPg, IOPcc) reported and stratified. Correlations were sought between the ORA parameters and the age, gender, and laterality. RESULTS: The study was conducted on 997 (502 right) eyes of 508 (234 males) normal individuals. The mean ± SD ages of the study groups were 14.7 ± 3.2, 25.9 ± 3.0, 35.3 ± 2.8, 44.6 ± 2.9, and 61.1 ± 7.7 years. The mean ± SD of the CH in the study groups were 10.9 ± 2.4, 9.8 ± 1.5, 9.8 ± 1.4, 9.7 ± 1.7, and 9.5 ± 1.6 mmHg and of the CRF were 10.9 ± 2.4, 9.5 ± 1.7, 9.4 ± 1.8, 9.6 ± 1.9, and 9.6 ± 1.8 mmHg. A statistically significant negative correlation was found between age and each of CH and CRF. IOPcc demonstrated a fairly constant trend in the different age groups whereas IOPg demonstrated an initial decline followed by a gradual rise over time. CONCLUSION: The corneal biomechanical properties CH and CRF decrease with age. IOPg and IOPcc change minimally with age.

Evaluation of the effect of corneal collagen cross-linking for keratoconus on the ocular higher-order aberrations.

BACKGROUND: Corneal collagen cross-linking (CXL) is the only treatment currently available to arrest the progression of keratoconus. The procedure consists of photopolymerization of stromal collagen fibers induced by combined action of a photosensitizing substance (riboflavin or vitamin B2) and ultraviolet-A light. PURPOSE: To determine changes in the ocular higher-order aberrations (HOAs) after CXL and its correlation with changes in visual acuity. DESIGN: Prospective interventional study. SUBJECTS AND METHODS: This study was conducted on 30 eyes of 16 patients with progressive keratoconus documented between 2012 and 2014. Patients were treated with epithelium-off CXL and followed for a minimum of 6 months. The following ocular HOAs were measured and analyzed using I-Tracey Aberrometer: coma, trefoil, spherical aberration, astigmatism, and total HOAs. RESULTS: There was statistically significant improvement in uncorrected visual acuity and best-corrected visual acuity between the preoperative and 6-month evaluations (P<0.001). Total HOAs and total coma were statistically significantly reduced at 6 months by 25% and 18%, respectively. Significant improvement was seen in spherical aberration by 8.71% (P<0.001), while no significant change was observed in trefoil and high order astigmatism (P=0.405 and 0.329, respectively). There was a statistically significant change in the average (K) value at the apex between the preoperative values and the 6-month values (P<0.05). CONCLUSION: Total HOAs, total coma, and spherical aberrations decreased after CXL. Coma has a direct relationship with the improvement of visual function.

Ocular response analyzer and goldmann applanation tonometry: a comparative study of findings.

PURPOSE: Correlation of findings of the Reichert Ocular Response Analyzer (ORA) with Goldmann applanation tonometry (GAT). DESIGN: Observational, cross-sectional study. METHODS: The study was conducted on 103 eyes of 56 patients, aged 41 to 78 years; average (±SD) 58.9 (±9.8) years attending the outpatient clinic of the Department of Ophthalmology, Alexandria University, for a routine refraction. Full ophthalmic examination including slit lamp biomicroscopy and GAT, then Reichert ORA utilization to obtain the intraocular pressure cornea corrected (IOPcc), the IOP Goldmann (IOPg), the corneal resistance factor (CRF), the corneal hysteresis (CH), and the central corneal thickness (CCT). Exclusion criteria included previous ophthalmic surgery and any corneal pathology. RESULTS: The mean (±SD) IOP GAT was 14.1 mm Hg (±3.0) (range: 8 to 22 mm Hg). The mean (±SD) IOPg, IOPcc, CRF, CH, and CCT was 15.5 (±4.0), 16.9 (±3.7), 9.6 (±2.0), 9.4 mm Hg (±1.7) and 540.8 (±32.6) µm, respectively. There was a significant correlation (P<0.0001) between IOP GAT and each of IOPg, IOPcc, and CRF; between IOPg and each of IOPcc, CRF, and CCT; between IOPcc and each of CRF and CH; and between CCT and each of CRF and CH at 0.01 level. The average (±SD) difference between IOP GAT and IOPg and IOPcc was -1.33 (±2.38) mm Hg and -2.81 (±2.66) mm Hg, respectively, and was statistically significant (paired t test in a 95% confidence interval). CONCLUSIONS: The ORA is valuable for the evaluation of IOP and corneal biomechanics. However its results are not to be used interchangeably with the GAT findings.