A comparison of the effect of donor-recipient trephine size disparity on refractive error in keratoconus.

OBJECTIVE To compare the effect of donor-recipient trephine-size disparity on spherical equivalent, and visual outcomes in penetrating keratoplasty for keratoconus. METHODS A prospective randomized clinical study conducted between April 2000 and April 2004 in the Ophthalmology Department, Shaheed Sadoughi Hospital, Yazd, Iran. Forty patients with keratoconus were randomly assigned to 2 groups. In group I (n=20) the patients were operated on with under-sized blade (0.25 mm disparity[D]), and in group II (n=20) with over-sized (0.50 mm D) trephine. RESULTS The spherical equivalent in group I was -2.61 +/- 2.81D, and -3.92 +/- 3.21D in group II. We found a better final visual acuity in group I compared with group II. More myopic shift was observed in group II, with greater disparity. Best-corrected visual acuity (BCVA) was better at the final follow-up in group I, compared with group II. Fourteen patients (70%) achieved BCVA 20/40 or better in group I, whereas in group II only 10 patients (5.0%) achieved this vision. Mean keratometry was 44.35D in group I, and 45.05D in group II. CONCLUSION We conclude that using donor-recipient under-sized trephine (0.25mm D) can be considered a reliable and effective method in reducing postoperative myopia.