Biometry results and outcomes in eyes with long and extreme axial lengths

Session Details

Session Title: Cataract Surgery Outcomes

Session Date/Time: Tuesday 16/09/2014 | 08:00-10:30

Paper Time: 09:56

Venue: Capital Hall A

First Author: : S.Ti SINGAPORE

Co Author(s): :    P. Woon   S. Chee           

Abstract Details

Purpose:

To study the biometry accuracy and refractive outcome in eyes with long (27.0-30.0mm) and extreme (>30.0mm) axial lengths (AL), correlation with intraocular lens A-constants and comparison between SRK/T and Haigis lens formulas.

Setting:

Singapore National Eye Centre

Methods:

The charts of Chinese patients with long axial lengths (>27.0mm), no other preoperative ocular morbidities and had uneventful phacoemulsification with implantation of a low-diopter (D) intraocular lens (IOL; Alcon MA60MA or AMO AR40M) over 1 year (2012) were retrospectively reviewed. Main parameters assessed were 1) AL measured by Zeiss IOL Master or contact ultrasound (keratometry by Topcon auto kerato-refractometer), 2) A-constants, 3) IOL model (categorized into positive-, zero- and negative-D lens) and 4) mean absolute error (MAE= 1-month postoperative spherical equivalent (SE)–predicted SE). The formula used for lens power calculation was SRK/T. Results were correlated to AL (Pearson’s correlation) and statistically compared to Haigis formula (repeated ANOVA). Statistical significance was set at p<0.05.

Results:

Results of 137 eyes of 112 patients (AL 27.0-30.0mm (n=44); AL >30.0mm (n=93)) were included. IOL categories: positive- D (n=72); zero-D (n=9); negative –D (n=42). A-constants used included both the standard and user group for laser interference biometry (ULIB) optimized A- constants. The MAE (n=123; SRK/T formula) was 1.14± 0.86D, and 91.1% had postoperative hyperopia (median+1.11D), with no significant correlation to AL. There was no significant difference in MAEs between IOL Master (n=97) and contact ultrasound techniques (n=26) (1.13±0.89D vs 1.14±0.74D, SRK/T formula, t-test, p=0.77). For the MA60MA IOL (n=88), ULIB optimized A- constants were significantly more accurate for low positive-D (MAE= 0.53±0.48D vs 1.29±0.96D, p<0.001) and negative-D IOLs (1.28±0.83D vs 2.03±0.63D, p=0.045) than standard A- constant. The Haigis formula more accurately predicted postoperative refractive error, with statistically lower MAE (MAE= 0.99±0.79D, p<0.001), and lower % postoperative hyperopia of 87% (median+0.89D). Differences in MAE obtained using SRK/T and Haigis formulae were significant only for AL >30mm (+1.28±0.9D and +1.06±0.86D respectively).

Conclusions:

In this cohort of long and extreme ALs, the MAE depended on IOL formula, A-constants used and ALs, with no difference in results derived from ultrasound biometry and IOL Master. The Haigis formula is more accurate than SRK/T formula at predicting refractive error in eyes longer than 30mm and should be the recommended choice. For IOL master, ULIB optimized A-constants for low-D IOL provided more accurate predictability of postoperative refractive error. Overall MAE was 1.14± 0.86D (median =1.1D), and 91.1% patients recorded hyperopia, suggesting that surgeons aiming for postoperative emmetropia should target at least myopia of ≥-1.1D.

Financial Interest:

NONE