Spherical equivalent refractive error of the pseudophakic eye with and without prior LASIK predicted using Gaussian optics

Abstract

Purpose : There is conflicting evidence for the need to take into account ocular aberrations instead of relying on Gaussian optics to accurately predict intraocular lens (IOL) power, particularly in post-LASIK eyes. The purpose was to evaluate if the refractive state of the pseudophakic eye can be accurately predicted using Gaussian optics in eyes with and without prior LASIK.

Methods : Following an IRB-approved protocol, 26 eyes of 16 pseudophakic subjects (34 to 88 years old), including 7 eyes of 5 post-LASIK subjects were enrolled. The following data was collected: manifest refraction, best-corrected distance visual acuity, corneal shape (Pentacam, Oculus, Wetzlar, Germany) and ocular distances measured from optical coherence tomography (OCT) images acquired with a custom-built extended-depth system that provides images ranging from anterior corneal surface to posterior retinal boundary (Figure 1) (Ruggeri et al, Biomed Opt Exp 7:1506-1520, 2012). A Gaussian eye model using two surfaces to model the cornea and a thin lens to model the IOL was created for each patient using measured ocular distances, mean radius of curvature of the central 3 mm zone of the corneal surfaces, and known IOL power. The thin lens was placed at the IOL posterior vertex measured in the OCT images. A backward ray-trace through the eye model was used to predict the spherical equivalent refraction (SEQ) in the spectacle plane. The difference between SEQ predicted with the eye model and actual post-operative SEQ was calculated for each subject.

Results : In the 19 eyes without history of LASIK, prediction error ranged from -0.40 D to 0.98 D with a mean absolute value of 0.26 ± 0.27 D, and with 11/19 eyes within ±0.25D and 15/19 eyes within ±0.50D. In the 7 post-LASIK eyes, the prediction error ranged from -0.88 D to 0.50 D with a mean absolute value of 0.40 ± 0.23 D, and with 2/7 eyes within ±0.25D and 6/7 eyes within ±0.50D.

Conclusions : The results suggest that the optics of the pseudophakic eye with or without history of LASIK can be accurately predicted using Gaussian optics.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Figure 1: Extended-depth OCT image of a pseudophakic eye. AEL:axial eye length; CCT: central corneal thickness; ACD: anterior chamber depth; VD: vitreous depth.

 

Figure 2: Prediction error of the pseudophakic spherical equivalent plotted in terms of axial eye length. Triangles: Eyes with no history of LASIK. Dots: post-LASIK eyes.