A Comparative Study on the Accuracy of IOL Calculation Formulas in Nanophthalmos and Relative Anterior Microphthalmos

center dot PURPOSE: We sought to compare the prediction accu-racy of 6 intraocular lens (IOL) formulas, namely, the Haigis, Hoffer Q, Holladay I, SRK/T, Barrett Universal II and Hoffer QST formulas, in microphthalmic eyes, in-cluding those with nanophthalmos and relative anterior microphthalmos (RAM).center dot DESIGN: Retrospective case series.center dot METHODS: Twenty-six eyes with nanophthalmos (axial length [AL] 16.84 +/- 1.36 mm, range 15.25 mm-19.82 mm) and 12 eyes with RAM (corneal diameter 8.41 +/- 0.92 mm, range 7.00 mm-9.50 mm) receiving cataract surgery were included. The IOL Master 500 was used for biometry; thus, lens thickness (LT) was omitted in the IOL power calculation. The mean and median arith-metic and absolute prediction errors (PEs) of the 6 origi-nal calculation formulas, the absolute PEs of the 6 formu-las after optimization, and the proportion of PEs within +/- 0.25 diopters (D), +/- 0.5 D, +/- 1 D, and +/- 2 D with each formula were compared. The factors influencing PE were analyzed by multivariate regression.center dot RESULTS: In the nanophthalmos group, the overall pre-diction results were shifted to myopia. The original Haigis formula had the smallest median absolute PE (1.61 D, P < 0.001), and the optimized Haigis formula had the high-est proportion of PEs within +/- 0.25 D, +/- 0.5 D, and +/- 1 D. In the RAM group, the overall prediction results were not significantly different from 0 ( P > .05). No signifi-cant difference was found among the formulas before op-timization ( P = .146) and after optimization ( P = .161),but the optimized Barrett Universal II formula had the highest proportion of PEs within +/- 1 D and +/- 2 D. center dot CONCLUSIONS: When omitting the LT parameter in the calculation, the Haigis formula was the most accurate in cataract patients with nanophthalmos (AL < 20 mm) among the 6 IOL calculation formulas, and the Barrett Universal II formula had the highest accuracy in cataract patients with RAM (corneal diameter <9.5 mm). (Am J Ophthalmol 2023;245: 61-69. (c) 2022 Elsevier Inc. All rights reserved.)