Screening of forme fruste keratoconus with the ocular response analyzer.

PURPOSE

To evaluate the performance of the Ocular Response Analyzer (ORA) in the screening of forme fruste keratoconus (FFKc).

METHODS

A retrospective comparative study was conducted involving 180 eyes. ORA preoperative data were analyzed for 125 normal control eyes (64 patients) undergoing laser in situ keratomileusis (LASIK) without corneal ectasia after 24 months of follow-up and 55 case eyes with unilateral keratoconus from a database (BCVA of 1.0, KISA index <60%). All eyes were matched in four groups of central corneal thickness (CCT): group 1, <500 microm; group 2, 500 to 539 microm; group 3, 540 to 579 microm; and group 4 >580 microm. Corneal hysteresis (CH), the corneal resistance factor (CRF), the air pressure curve, and the infrared signal were compared between FFKc and normal eyes in each group.

RESULTS

The mean CH was 9.1 +/- 1.8 mm Hg for FFKc and 10.3 +/- 1.9 mm Hg for control eyes (P < 0.001), and the mean CRF was 9.2 +/- 1.8 and 11.1 +/- 2 mm Hg (P < 0.001), respectively. Sensitivity in each group was as follows: group 1, CH < 9.5 mm Hg (91%) and CRF < 9.5 mm Hg (81%); group 2, CH < 10.5 mm Hg (91%) and CRF < 10 mm Hg (87%); group 3, CH < 11.5 mm Hg (79%) and CRF < 11 mm Hg (74%); group 4 had two cases of FFKc, and the difference was not significant. Air pressure levels at inward and outward applanation and the maximum air pressure level were significantly lower and shorter in time in FFKc (P < 0.001), whereas the shape of the infrared signal was more variable.

CONCLUSIONS

The ORA provides additional information in the screening of FFKc, with an accurate analysis of the corneal biomechanical properties according to CCT, air pressure, and infrared curves.