Intraocular lens power in bilateral cataract surgery: whether adjusting for error of predicted refraction in the first eye improves prediction in the second eye

Abstract

Purpose: To assess whether the retrospectively calculated intraocular lens (IOL) position value in the first eye reduces the error of predicted refraction in the second.

Setting: Prince of Wales Hospital, Sydney, Australia.

Methods: One hundred twenty-one consecutive patients who had bilateral cataract surgery with the same IOL (SI-30NB, Advanced Medical Optics) were identified. The case-derived A-constant in the first eye was calculated from the postoperative refraction. This value was used to calculate the adjusted error of predicted refraction in the second eye and compared against the unadjusted error in that eye (calculated using manufacturer's A-constant).

Results: Axial length (r = 0.97), corneal power (r = 0.97), and IOL power (r = 0.90) were strongly correlated between eyes with no statistically significant mean interocular difference. Although there was no significant interocular difference in the mean error of predicted refraction (SRK/T), there was only a moderate correlation between eyes (r = 0.40). Using the axial length vergence formula, the mean adjusted error of predicted refraction in the second eye (-0.66 diopter [D]) was significantly larger than the mean unadjusted error (-0.47 D) (P = .029). The standard deviation of the adjusted error of predicted refraction (SRK/T) in the second eye (0.85 D) was greater than the standard deviation of the unadjusted error (0.79). Similarly, the adjusted mean absolute error of predicted refraction (0.65 D) was greater than the unadjusted error (0.63 D).

Conclusion: Adjusting the IOL power in the second eye by the amount of overprediction or underprediction in the first eye did not improve prediction accuracy because the error of predicted refraction varied independently between the 2 eyes of an individual.