To evaluate biometric changes after mitomycin C (MMC) augmented trabeculectomy and their effect on intraocular lens (IOL) power calculation using different formulas.

In this prospective, interventional case series study, 34 eyes of 31 phakic glaucoma patients who were scheduled for primary trabeculectomy were enrolled. Using a non-contact biometry device (LenStar, Haag-Streit AG, Koeniz, Switzerland) axial length (AL), mean corneal power and IOL power were calculated with the SRK/II, SRK/T, Holladay and Hoffer Q formulas one day before surgery and compared to those obtained 3 and 6 months after the operation. Bland-Altman plot was used to determine the agreement between pre- and postoperative IOL power values.

AL was significantly decreased at month 3 (-0.14±0.13 mm) and month 6 (-0.14±0.15 mm) as compared to baseline values (both P values<0.001). Mean corneal power increased significantly at month 3 (0.41±0.46 diopters (D); P<0.001) and month 6 (0.27±0.47 D; P=0.008). Using different formulas, IOL power did not change significantly after the operation (all Ps≥0.17). IOL power changes using the SRK/II formula were 0.04±0.76 (P=0.738) and 0.2±0.74 D (P=0.187) at 3 and 6 months respectively; corresponding values were 0.01±0.64 (P=0.895) and 0.2±0.71 D (P=0.17) for SRK/T, -0.1±0.75 (P=0.427) and 0.16±0.79 D (P=0.319) using Holladay, and -0.09±0.76 (P=0.505) and 0.14±0.9 D (P=0.442) employing the Hoffer Q formula.

Despite significant changes in AL and corneal power after trabeculectomy, IOL power calculation remains unchanged; therefore adjustment of IOL power calculation after trabeculectomy seems unnecessary.