Biomechanical Property of Keratoconus Measured by ORA

PURPOSE: To compare the biomechanical properties of keratoconus, keratoconus suspect, and normal subjects measured by ocular response analyzer. METHODS: A total of 72 patients were divided into 3 groups: keratoconus, suspected keratoconus, and normal control subjects. The 3 age-matched groups were evaluated according to age, sex, and visual acuity. Slit lamp examinations, Pentacam, and ocular response analyzer (ORA) examinations were performed. Mean corneal refractive power, central corneal thickness, corneal hysteresis (CH), and corneal resistance factor (CRF) were evaluated and analyzed. RESULTS: Twenty-four eyes were included in each group. The mean age was 23.8 years in keratoconus, 26.0 years in suspected keratoconus and 26.1 years in normal subject groups. Mean corneal refractive power was significantly higher in keratoconus (p < 0.001) and suspected keratoconus (p = 0.001) groups than in the normal subject group. Mean central corneal thickness showed significant differences among the 3 groups (p < 0.05). CH was significantly lower in keratoconus than suspected keratoconus (p = 0.025) and normal subject groups (p = 0.005), but showed no significant difference between suspected keratoconus and normal subject groups. CRF showed significant differences among all 3 groups (p < 0.05). CH and CRF had negative correlations with mean corneal refractive power and positive correlations with central corneal thickness. CONCLUSIONS: CH and CRF measured by ORA were significantly different between keratoconus and normal subject groups and had significant correlations with mean corneal refractive power and central corneal thickness. CRF may be a useful method to differentiate between suspected keratoconus and normal cornea patients.

Corneal Topographic Study Using Orbscan II between Keratoconus and Keratoconus Suspect

PURPOSE: To compare corneal topographic changes using Orbscn II between keratoconus and keratoconus- suspected eyes. METHODS: Thirty-seven keratoconus eyes, 17 keratoconus-suspected eyes and 37 normal eyes were evaluated by using Orbscan II corneal topography. We compared central phachymetry, anterior elevation from best-fit sphere (BFS), posterior elevation from BFS, most protruded corneal thickness, central corneal thickness, anterior chamber depth, corneal diameter, and pupil size. RESULTS: Central pachymetry, anterior and posterior elevation from BFS, central corneal thickness, and anterior chamber depth were statistically significantly different between keratoconus and control eyes. Anterior elevation from BFS showed a significant difference between keratoconus-suspected and control eyes. There were statistically significant differences in central pachymetry, posterior elevation from BFS, central corneal thickness and most protruded corneal thickness between keratoconus and keratoconus-suspected eyes. Corneal diameter and pupil size showed no differences among the 3 groups. CONCLUSIONS: Suspected keratoconus eyes have a higher value of anterior elevation from BFS on Orbscan II topography as compared with control eyes. Central pachymetry, posterior elevation from BFS, central corneal thickness and most protruded corneal thickness may be helpful in distinguishing between keratoconus and keratoconus-suspected eyes.