The AS biometry technique-A novel technique to aid accurate intraocular lens power calculation after corneal laser refractive surgery

Intraocular lens power (IOL) calculation for cataract surgery has been shown to be inaccurate after photorefractive keratectomy (PRK), laser-assisted subepithelial keratectomy (LASEK) and laser in situ keratomileusis (LASIK). Many techniques exist to calculate corneal power with varying results and require the clinician to be aware of the pitfalls of IOL power calculation in post-refractive eyes. The AS biometry method proposed here is a simple method which does not rely on the calculation of corneal power. This new method is compared to the current gold standard the clinical history method (CHM). Twenty-nine eyes of 15 patients had routine biometry prior to LASIK, LASEK or PRK. The range of pre-operative spherical equivalent refractive error was -5.37 to +4.00 diopters. The post-operative refraction was measured at 3-6 months. The IOL power calculation was calculated using the AS biometry method and the CHM. The two methods were compared using the Student's paired t-test and the Bland Altman technique. There was no statistical difference between the AS biometry method and the CHM. The paired Student's t-test comparing the AS biometry method and the CHM showed no statistical difference, t = 0.33 with a p-value of 0.75, at a 95% confidence interval. The authors conclude that the AS biometry technique is as accurate as the CHM. The former is a simpler method which avoids many of the pitfalls and confounding factors involved in IOL power calculation following corneal excimer laser surgery. However, like the CHM it requires measurements prior to laser surgery.