The effect of penetrating keratoplasty on contrast sensitivity in keratoconus

Complaints of visual distortion often precede a decrement in visual acuity in keratoconus. We studied seven patients with keratoconus who had undergone keratoplasty in one eye and whose Snellen visual acuity measurements were equal in the grafted and nongrafted eyes. Subjects were examined clinically; we then measured contrast thresholds for seven spatial frequencies of computer-generated sinusoidal gratings after optimal contact lens correction. Results indicate that nongrafted keratoconic eyes demonstrate abnormal contrast sensitivity, even with good visual acuity measurements. Eyes with clear corneal grafts and with visual acuities comparable to nongrafted eyes fell within the 95% confidence limits of the normal contrast sensitivity curve. The findings confirm that corneal distortion or opacity in the optimally corrected keratoconic eye may account for notable visual dysfunction and that keratoplasty improves not only Snellen visual acuity but contrast sensitivity as well.