Accuracy of partial coherence interferometry in patients with large inter-eye axial length difference

Abstract

Purpose : Accurate pre-operative biometry is essential for intraocular lens (IOL) selection in cataract surgery, and is commonly obtained with partial coherence interferometry (PCI). A difference of >0.3 mm in axial length (AL) between eyes on PCI measurement often triggers confirmatory measurements. To determine whether re-measurement is necessary in patients with large inter-eye AL difference, we compared the observed-expected post-op spherical equivalent (SE) between patients with and without an inter-eye AL difference of >0.3 mm.

Methods : Retrospective chart review of all patients having cataract surgery at one institution from 7/2014 through 6/2015. Exclusion criteria were: IOLMaster SNR<100, pre-operative cylinder >3D, toric IOL, history of refractive surgery, combined surgery, any intra- or post-op complication, or POM1 BCVA <20/20. Control patients without an inter-eye AL difference >0.3 mm were matched for age, sex, and AL. IOL Consultant was used to determine the expected post-op refraction for the implanted IOL using Holladay II, SRK-T, and Hoffer Q formulae. The difference between the observed post-op refraction SE at post-op month one (POM1) and the expected SE was recorded . Mann-Whitney U Test and two-tailed Fisher’s exact test was used for analysis.

Results : 1218 surgeries were reviewed: 70 eyes of 51 patients met inclusion criteria and were matched to 70 control eyes. Mann-Whitney U Testing found no significant difference between the observed-expected POM1 SE for any formula (Table 1). Two-tailed Fisher's exact test found no significant difference in the number of cases vs controls with a post-operative SE ≥ 0.5 D or 1.0 D different from the expected POM1 SE outcome (Table 2).

Conclusions : Good-quality PCI data is equally accurate in patients with or without an inter-eye AL difference > 0.3 mm, with no statistically significant difference in the observed-expected SE on POM1 refraction for patients with vs without a >0.3 mm difference in AL using IOLMaster 500 pre-operative biometry measurements. Confirmatory AL measurements (e.g. with immersion A-scan biometry) in patients with large inter-eye AL difference may not be necessary.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Table 1. Mann-Whitney U Test for the mean observed-expected POM1 SE.

 

Table 2. Fisher's Exact Test for difference in the proportion of patients with at least 0.5 D or 1.0 D difference in the observed minus expected POM1 SE.