The effect of penetrating keratoplasty on contrast sensitivity in keratoconus
M. J. Mannis, K. Zadnik and C. A. Johnson
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.
