Comparative accuracy of IOL power calculation formulas in nanophthalmic eyes undergoing cataract surgery

Abstract

Aim: To compare the predictive accuracy of three widely used IOL power calculation formulas—Hoffer Q, SRK/T, and SRK II—in adult patients with nanophthalmos undergoing cataract surgery or clear lens extraction. Methods: This retrospective observational study included 45 eyes with axial lengths ≤ 20.5 mm diagnosed with nanophthalmos. All patients underwent uncomplicated cataract surgery or clear lens extraction with posterior chamber IOL implantation. Preoperative biometry was performed using ZEISS IOL Master 700 or NANO AXIS A-scan. IOL power was calculated using Hoffer Q, SRK/T, and SRK II formulas. Postoperative spherical equivalent was recorded at one month, and prediction error was calculated as the difference between actual and predicted refraction. Mean absolute error (MAE) and percentage of eyes within ±0.25 D, ±0.50 D, ±1.00 D, and ±2.00 D were assessed. Statistical analysis included one-sample t-tests and descriptive statistics using SPSS version 26. Results: The Hoffer Q formula showed the lowest mean absolute prediction error (−0.44 ± 0.30 D), followed by SRK/T (+0.68 ± 0.73 D), while SRK II exhibited the highest error (+3.28 ± 0.52 D). The Hoffer Q formula demonstrated superior accuracy, with 75.6% of eyes within ±0.50 D and 93.3% within ±1.00 D of the target refraction. SRK II showed a statistically significant hyperopic shift (p < 0.001), whereas Hoffer Q and SRK/T did not show statistically significant differences from zero prediction error. Conclusion: Among the three formulas studied, the Hoffer Q formula provided the most accurate IOL power prediction in nanophthalmic eyes, with the lowest refractive error and highest consistency. These findings support the use of Hoffer Q in managing cataract patients with nanophthalmos and highlight the need for further evaluation of advanced formulas in this subgroup.