[Subclinical keratoconus diagnosis by elevation topography].

PURPOSE

To evaluate the most effective parameters of Orbscan Corneal Topography System for subclinical keratoconus screening.

METHODS

The study includes corneas from patients with clinical diagnosis of keratoconus (group 1, n=35), patients with subclinical keratoconus (group 2, n=14) and a control group of myopic subjects paired in gender, age and refractive spherical equivalent (group 3, n=35). Placement of the apex, anterior and posterior corneal elevation, minimal corneal thickness, anterior chamber depth and corneal diameter were evaluated.

RESULTS

The most frequent location of the apex was at the inferotemporal sector (53%). Mean anterior elevation was 56.73 S.D. 25.95 mm in group 1 and 20.35 S.D. 8.04 mm in group 2; results that are statistically significant different from the control group (p<0.001). Mean posterior elevation was 126.23 S.D. 57.7 mm in group 1 and 54.28 S.D. 19.55 mm in group 2, both showing a statistically significant difference from the control group (p<0.001). Minimal corneal thickness and anterior chamber depth also showed statistically significant differences between the three groups. No differences were found in corneal diameter values.

CONCLUSIONS

Statistically significant differences were found in anterior and posterior elevation, minimal corneal thickness and anterior chamber depth parameters, as measured by the Orbscan system, between normal myopic subjects and those with clinical and sub-clinical keratoconus. These parameters should be considered in the detection of patients with increased risk for developing secondary keratectasia following corneal refractive surgery.