EyeWorld India September 2019 Issue

EWAP SEPTEMBER 2019 63 CORNEA Contact information Breen: michael.breen@alcon.com D[ 5VGHCPKG 2GVTQW $KPFGT /& EyeWorld Contributing Writer This article originally appeared in the June 2019 issue of EyeWorld . It has been UNKIJVN[ OQFKƂGF CPF CRRGCTU JGTG YKVJ permission from the ASCRS Ophthalmic Services Corp. A study involving nearly 2,000 eyes suggests that calculations incorporating intraoperative aberrometry (IA) outperform preoperative calculations, with the difference even more pronounced when IA suggested a different IOL power from preoperative measurements. Evolving beyond formulae The evolution of IOL power calculations has resulted in improved, more reliable refractive outcomes in cataract ÃÕÀ}iÀÞ° ÕÌ >ViÛ} Ìi predicted postoperative spherical equivalent is still `vwVÕÌ >}«iÀViÌ>}i v iÞiÃ] ÜÌÕÃÌ ÛiÀ>v v eyes demonstrating a residual ÀivÀ>VÌÛi VÞ`iÀ v ćä°xä ] according to one study, 1 only 55% of cases reaching actual emmetropia according to another study, 2 and long axial lengths presenting a continued challenge to obtain target outcomes. 3 Intraoperative aberrometry, through its use of an aphakic refraction-based calculation, has been shown to help improve refractive outcomes in cataract surgery, according to V>i Àii] " ] Ü Ã«i at the 36th Congress of the European Society of Cataract >` ,ivÀ>VÌÛi -ÕÀ}iÃ° 7i IA has shown encouraging outcomes, he said extensive data is lacking on how it could improve refractive outcomes in long eyes. IA in patients with bilateral cataracts undergoing toric IOL implantation increased the proportion of eyes with postoperative refractive astigmatism of 0.50 D or less and reduced the mean postoperative refractive astigmatism at 1 month, compared to standard methods, according to a study. 4 An unrelated study found 67% of eyes with prior myopic LASIK or PRK came within ±0.5 D of IA’s predicted outcome, compared to 46% with conventional preoperative methodology. 5 Assessing IA In a retrospective analysis, Dr. Àii i` vÀ `vviÀiViÃ between the absolute prediction error using an IA driven calculation for IOL power determination and the absolute prediction error that would have resulted had the surgeon’s preoperative plan been followed. i ViVÌi` «ÃÌ«iÀ>ÌÛi data from the ORA System (Alcon) from multiple centers in the U.S. The ORA Analyzor database stores patient preoperative, intraoperative, and postoperative data on a secure server. The database had more than 1 million cataract surgeries recorded, roughly 300,000 of which included postoperative data. Of those, 35,766 entries >` Ìi Ã«iVwi` VÕÃ criteria, 1,786 of which had axial lengths over 26.5 mm and a single-piece acrylic IOL platform. À° ÀiiÞ«ÌiÃâi` that the absolute prediction error would be lower with IA and the proportion of eyes with postoperative absolute «Ài`VÌ iÀÀÀ ćä°xä v the predicted postoperative SE would be higher with IA compared to the preoperative plan. Ten percent of the eyes were randomly selected for hypothesis development and 90% were used for hypothesis VwÀ>ÌÀÞ >>ÞÃÃ° None of the eyes had a history of surgery, prior refractive surgery, or ocular disease. IA calculations were driven by the measured aphakic spherical equivalent (SE). º/i V>VÕ>Ì Üi `` vÀ prediction error was fairly basic,” À° Àii Ã>`° º Ì Ü>Ã Ìi Ƃ predicted postoperative SE minus the actual postoperative SE. The absolute prediction error for the preoperative calculation was the difference between the power implanted and the IOL power based on the preoperative calculation, actual postoperative SE, and the back-calculated postoperative SE prediction error had the preoperative IOL power been implanted,” he said. The results showed that both the mean and median preoperative prediction errors ÜiÀi Ã}wV>ÌÞ }Ài>ÌiÀ Ì> Ìi Ƃ «Ài`VÌ iÀÀÀ° º/iÀi ÜiÀi Ã}wV>Ì `vviÀiViÃ in both PEs, that is the mean absolute and the median IOL power calculations incorporating intraoperative aberrometry