Reliability of intraocular lens power calculation after cataract surgery in patients with relative anterior microphthalmos.

Abstract

Patients with relative anterior microphthalmus (RAM) are characterized by special anatomical features (corneal diameters <11 mm, anterior chamber depth <2 mm and normal axial length) that sometimes make intraocular lens (IOL) power calculation difficult. Seventy-five patients aged 75.6+/-10.3 years with RAM were evaluated for preoperative target refraction and postoperative refraction after cataract surgery. We used biometric formulas as modified by Haigis for IOL power calculation. The average IOL power implanted was 25.2+/-2.8 dptr (one-piece all-PMMA IOL; range 19-31 dptr). The preoperatively calculated target refraction was -0.71+/-1.43 dptr (range -4.3 to +2.2 dptr). The average postoperative spherical equivalent was -0.41+/-1.50 dptr (range -5.5 to +6.0 dptr). The mean difference between target and end refraction was -0.30+/-1.54 dptr Fifty-seven percent of cases did not differ by more than 1 dptr from target refraction, 81.3% by not more than 2 dptr, and 94.7% by not more than 3 dptr; only 5.3% of cases deviated by more than 3 dptr. There was no correlation of the amount of deviation between target and postoperative refraction with axial length, corneal diameter and anterior chamber depth. There was, however, a significant correlation between target refraction and amount of deviation of spherical equivalent. The largest differences were found with target refractions greater than +2 dptr. In spite of the special anatomical conditions in patients with RAM the biometric formulas as modified by Haigis produced reliable IOL power calculations. The best accuracy was achieved when aiming at a target refraction in the range of +/-2 dptr.