Keratoconus associated with cone-rod dystrophy: a case report.

A 31-year-old man with bilateral keratoconus associated with apical corneal scarring underwent uneventful penetrating keratoplasty in his left eye. Postoperatively his best-corrected visual acuity did not improve beyond 20/120. Examination of the fundus revealed features suggestive of bull's eye maculopathy. On performing an electroretinogram study of both eyes, grossly delayed implicit time with reduced amplitudes of the rod response and extinguished cone waveforms were noted, indicating cone-rod dystrophy. Color blindness was also noted on testing with Ishihara's pseudoisochromatic plates. Genetic counseling showed this to be an isolated defect with negative family history. Preoperative electrophysiologic studies may have a prognostic role in these cases.