Intraocular Lens Power Calculation for Eyes with High and Low Average Keratometry Readings: Comparison Between Various Formulas

Purpose: To compare the accuracy of intraocular lens power prediction for eyes with average keratometry (K) readings greater than 46.00 diopters (D) and lower than 42.00 D.

Setting: Ein-Tal Eye Center, Tel-Aviv, Israel.

Design: Retrospective case series.

Methods: Eyes having cataract extraction surgery with steep and flat preoperative corneal curvatures determined with the Lenstar-LS900 device were enrolled. Refractive prediction errors for the Barrett Universal II, Haigis, Hill-RBF, Hoffer-Q, Holladay 1, Holladay 2, Olsen, and SRK/T formulas were compared. Optimized K values for the SRK/T formula were back-calculated for each group. Validation was performed using an additional dataset.

Results: The study comprised 171 eyes (79, K reading >46.00 D; 92, K reading <42.00 D). For K readings greater than 46.00 D, myopic errors were noted using the SRK/T and Hill-RBF formulas and hyperopic errors using the Olsen C-constant and Haigis (-0.31 D, -0.17 D, 0.18 D, and 0.17 D, respectively). The percentage of eyes with an absolute error within ±0.50 D from target refraction ranged from 60.8% (SRK/T) to 83.0% (Hill-RBF). For K readings lower than 42.00 D, myopic errors were seen using the Haigis, Hill-RBF, Hoffer-Q, and Olsen-C formulas (-0.31 D, -0.14 D, -0.22 D, and -0.17 D, respectively) and a hyperopic error using the SRK/T formula (0.16 D). The refractive prediction within ±0.50 D ranged between 75.0% (Haigis) and 96.7% (Barrett Universal II).

Conclusions: Power calculation for eyes with flat corneas and steep corneas requires the use of specific formulas for accurate postoperative results. An adjustment method of the SRK/T formula is proposed.