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

Background: Patients with relative anterior microphthalmus (RAM) are charac terized by special anatomical features (corneal diameters <11 mm, anterior chamber depth <2 mm and normal axial length) that sometimes make intraocula r lens (IOL) power calculation difficult. Patients and methods: Seventy-fiv e patients aged 75.6+/-10.3 years with RAM were evaluated for preoperative target refraction and postoperative refraction after cataract surgery. We u sed biometric formulas as modified by Haigis for IOL power calculation. Res ults: The average IOL power implanted was 25.2+/-2.8 dptr (one-piece all-PM MA 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 s pherical equivalent was -0.41+/-1.50 dptr (range -5.5 to +6.0 dptr). The me an 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 refr action, 81.3% by not more than 2 dptr, and 94.7% by not more than 3 dptr; o nly 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 a xial length, corneal diameter and anterior chamber depth. There was, howeve r, a significant correlation between target refraction and amount of deviat ion of spherical equivalent. The largest differences were found with target refractions greater than +2 dptr. Conclusions: In spite of the special ana tomical conditions in patients with RAM the biometric formulas as modified by Haigis produced reliable IOL power calculations. The best accuracy was a chieved when aiming at a target refraction in the range of +/-2 dptr.