New method to assess the accuracy of intraocular lens power calculation formulas according to ocular biometric parameters

Abstract

Purpose: To develop a new method that makes it easy to detect accuracy deficiencies of any intraocular lens power calculation formulae and to test it on 9 different formulae. Setting: IOA, Madrid, Spain Design: Retrospective observational case series. Methods: This study’s first stage included 3519 eyes from 3519 candidates to cataract surgery for which frequency distributions for the following biometric eye parameters were computed: axial length (AXL), anterior-chamber depth (ACD), lens thickness (LT), white-to-white (WTW) and mean corneal radius (Rm). The resulting data for each parameter were 5th, 25th, 75th and 95th percentile, which allowed us to define the corresponding normality range. In a second stage, the new graphic-representation method was tested for 9 different formulae in a sample of 70 eyes undergoing cataract surgery with multifocal intraocular lens (MIOL) implantation. Results: Normality ranges (defined as the 25th-to-75th-percentile interval) were 22.84 to 24.42 mm for AXL, 2.86 to 3.39 mm for ACD, 4.36 to 4.88 mm for LT, 11.64 to 12.19 mm for WTW and 7.52 to 7.87 mm for Rm, with lower sizes in women. No significant differences were found along the 9 formulae for percentage of eyes in ±0.50D (p=0.82) or ±1.00D (p=0.97). The new graphical method showed less accuracy in ±0.50 D for ACDs from 2.46 to 2.85 mm (5th to 25th percentile) for several formulae (p<0.05). Conclusions: 9 formulae showed non-significant differences in the general predictability for a sample of eyes candidates to MIOL implantation. Predictability in this sample decreased for short ACDs.