Biomechanical characteristics of the ectatic cornea.

The ocular response analyzer (ORA) (Reichert, Inc.) was used in the case of a middle-aged man who developed unilateral corneal ectasia after bilateral laser in situ keratomileusis (LASIK). The preoperative refraction was similar in the 2 eyes. Post-LASIK ectasia was central in the left eye; topography was oblate in the right eye. The ORA values consisted of the mean of 4 measurements. Corneal hysteresis and corneal resistance factor were almost equal in the ectatic eye and the nonectatic eye. However, significant between-eye differences in the morphology of the signals were noted, most prominently in the lower amplitude of the applanation peaks in the ectatic eye. The shape of the applanation signal yielded important information in addition to corneal hysteresis and corneal resistance factor.