Intraocular lens calculation by intraoperative autorefraction in myopic eyes

The purpose was to provide a formula to calculate intraocular lens (IOL) power by intraoperative autorefraction in myopic refractive lens exchange (RLE).

This was a prospective, noncomparative consecutive case series, including 82 eyes of 82 patients with age superior to 45 years and mean preoperative spherical equivalent (SE) -12.84 diopters (D) [standard deviation (SD) 6.24, range -3 to -27]. Autorefraction was performed by a hand-held instrument during phacoemulsification after cortex removal and the IOL power calculated from the resulting aphakic SE by two existing restricted formulas (personal for high myopia and Ianchulev for low myopia). In each eye, subjective refraction 2 months postoperatively and implanted IOL were used to retrospectively calculate the IOL power achieving plano (predicted final adjusted IOL power). The relation between aphakic SE at intraoperative autorefraction (x, independent variable) and predicted final adjusted IOL power (y, dependent variable) was studied.

A relation between SE at intraoperative autorefraction and predicted final adjusted IOL power for the whole series range was expressed by the parabola y=0.07x(2)+1.27x+1.22. Previous restricted formulas achieved a good predictability in their specific range with a mean postoperative SE of -0.58 D (SD 0.73, range -3 to 0.75) and a mean defocus equivalent of 0.69 D (SD 0.62, range 0 to 3).

The parabolic relation accounts for previous different regression lines in different myopic ranges. Intraoperative autorefraction is a reliable alternative to standard biometry in myopic eyes. A table for clinical use is provided.