Intraocular Lens Power Change after Trabeculectomy

To describe the biometric changes and their effect on intraocular lens (IOL) power calculation after trabeculectomy and to compare the accuracy of four formulas namely SRK/II, SRK/T, Holladay and Hoffer Q for IOL power calculation in these patients. Thirty-four eyes of 31 glaucoma patients who were scheduled for primary trabeculectomy were enrolled. A non-contact biometry device (LenSTAR) was used to measure mean corneal power, axial length, and IOL power, calculated with SRK/T, SRK/II, Holladay and Hoffer Q formulas, in the day before trabeculectomy and 3 and 6 months postoperatively. Postoperative measurements were compared with preoperative values and Bland-Altman plots were used to investigate the agreement between pre and postoperative calculated IOL powers. At postoperative months 3 and 6, axial length decreased by 0.14±0.13 and 0.14±0.15 mm (p<0.001) at, respectively and mean corneal power increased by -0.41±0.46 diopter (p<0.001) and -0.27±0.47 diopters (p=0.008), respectively. Calculated IOL powers were not significantly different from preoperative values (SRK/T formula: -0.01±0.64 (p=0.895) at months 3 and -0.2±0.71 diopters (p=0.17) at months 6, SRK/II formula: - 0.04±0.76 (p=0.738) at months 3 and -0.2±0.74 diopters (p=0.187) at months 6, Holladay formula: 0.1±0.75 (p=0.427) at months 3 and -0.16±0.79 diopters (p=0.319) at months 6, Hoffer Q formula: 0.09±0.76 (p=0.505) at months 3 and -0.14±0.9 diopters (p=0.442) at months 6). After trabeculectomy, the decrease in axial length negated the increase in corneal power which resulted in a non-significant change in postoperative calculated IOL powers as compared to preoperative values.