Comparison of accuracy of online formulas for IOL power calculation after myopic excimer surgery

Session Details

Session Title: IOL Power Calculations

Session Date/Time: Sunday 11/09/2016 | 16:00-18:00

Paper Time: 17:44

Venue: Hall C2

First Author: : R.Chaudhuri INDIA

Co Author(s): :    R. Dutta   N. Shroff                 

Abstract Details

Purpose:

To compare the accuracy of various formulas provided by the ASCRS Post Keratorefractive Online Calculator for IOL power calculation in eyes with previous myopic excimer laser surgery.

Setting:

Cataract & IOL Service, Shroff Eye Centre, A-9 Kailash Colony, New Delhi, India.

Methods:

A retrospective analysis of 81 eyes of 63 patients with history of previous myopic LASIK/PRK undergoing cataract surgery with IOL implantation was done at least 6 months post-operatively. Nine formulas provided by the ASCRS Post- Keratorefractive Online Calculator were used: Adjusted Atlas-9000, Adjusted Atlas Ring, Masket Formula, Modified Masket, Barrett True-K, Wang-Koch-Maloney, Shammas, Haigis-L and Barrett True-K No History. The optimum IOL power corresponding to the target refraction was back-calculated using the stable post IOL implantation refraction and implanted IOL power. The optimum IOL power was compared with the IOL power predicted by each formula.

Results:

The mean age was 48.96±10.7 years. 61 eyes (75.3%) achieved a post-operative spherical equivalent of within ±1.00D. The mean logMAR UCVA was 0.16±0.14. On comparing predicted IOL power with optimum IOL power, the differences were not significant with Shammas (p=.983), Haigis-L (p=.116), Barrett No-History (p=.106) and Adjusted Atlas Ring (p=.064) formulas. The differences were significant with other formulas (p<.05). The Shammas and Haigis-L formulas gave the least prediction errors (0.004±0.95D and -0.40±1.23D respectively). The prediction error difference between Shammas and Haigis-L was significant (p=.006). The Shammas formula produced the highest percentage (80% eyes) within ±1.00D of optimum IOL power.

Conclusions:

The “No History” formulas provided by the ASCRS Online Calculator are more accurate than those which rely on pre refractive surgery data. In this study, the Shammas and Haigis-L formulas gave the least prediction errors. The most accurate and predictable IOL power formula for eyes undergoing cataract surgery with previous myopic excimer correction was the Shammas formula.

Financial Disclosure:

NONE