Predicting postoperative anterior chamber depth in cataract patients using Scheimpflug slit photography

To predict the postoperative anterior chamber (AC) depth from the preoperative in situ position of the lens central clear zone (CCZ) using Scheimpflug slit photography.

111 eyes of 78 cases that underwent phacoemulsification and intraocular lens (IOL) implantation were examined. 748 eyes of 383 healthy subjects with transparent lenses were used as the control. Scheimpflug slit photography was done under maximal mydriasis, and biometry was performed on the photographs. Two types of acrylic IOLs (MA30BA and MA60BM, both from Alcon) were used in this study. The preoperative AC depth (L1), the distance between the anterior lens capsule and lens CCZ (L2) and the postoperative AC depth (I1) were determined. I2, the predicted postoperative AC depth, was then determined from a linear regression of L1 + L2 and I1.

L2 thickened by 0.014 mm/year, and L1 decreased by 0.016 mm/year in the transparent lenses. L1 + L2 changed little with aging in both cataractous and transparent lenses. L1 + L2 and I1 showed a linear correlation with r = 0.80 in the MA30BA and r = 0.77 in the MA60BM groups. The mean error values between I1 and I2 were 0.095 +/- 0.096 and 0.123 +/- 0.114 mm in MA30BA and MA60BM, respectively. The error between I1 and I2 was within +/- 0.17 and +/- 0.33 mm or less in 72.9 and 91.5% of MA30BA and in 82.7 and 96.2% of MA60BM. In contrast, the error between I2 and I1 when calculated using the SRK/T formula was much larger - in excess of +/- 0.33 mm in 38.7% of the eyes.

L1 + L2 changes little with aging and is considered a useful marker of the position of the crystalline lens in situ. There was a high correlation between I1 and L1 + L2. These allow a far more accurate prediction of I1 than previous methods. In combination with the conventional regression formula and ray tracing, a highly accurate IOL power calculation can be attained.