An innovative approach for determining the customized refractive index of ectatic corneas in cataractous patients

Shiva Pirhadi,Keivan Maghooli,Khosrow Jadidi

doi:10.1038/s41598-020-73492-4

Abstract

The aim of this study is to determine the customized refractive index of ectatic corneas and also propose a method for determining the corneal and IOL power in these eyes. Seven eyes with moderate and severe corneal ectatic disorders, which had been under cataract surgery, were included. At least three months after cataract surgery, axial length, cornea, IOL thickness and the distance between IOL from cornea, and aberrometry were measured. All the measured points of the posterior and anterior parts of the cornea converted to points cloud and surface by using the MATLAB and Solidworks software. The implanted IOLs were designed by Zemax software. The ray tracing analysis was performed on the customized eye models, and the corneal refractive index was determined by minimizing the difference between the measured aberrations from the device and resulted aberrations from the simulation. Then, by the use of preoperative corneal images, corneal power was calculated by considering the anterior and posterior parts of the cornea and refractive index of 1.376 and the customized corneal refractive index in different regions and finally it was entered into the IOL power calculation formulas. The corneal power in the 4 mm region and the Barrett formula resulted the prediction error of six eyes within ± 1 diopter. It seems that using the total corneal power along with the Barrett formula can prevent postoperative hyperopic shift, especially in eyes with advanced ectatic disorders.

Highlights

The aim of this study is to determine the customized refractive index of ectatic corneas and propose a method for determining the corneal and IOL power in these eyes
The accurate IOL power calculation is a challenge, while determining the correct IOL power plays an important role in achieving acceptable visual results and optimal refractive and in patients satisfaction after cataract surgery
The number of eyes entered into this study is not high, based on to our best knowledge, this is the first study that focuses on determining the refractive index of the cornea in patients with keratoconus

Summary

Introduction

The aim of this study is to determine the customized refractive index of ectatic corneas and propose a method for determining the corneal and IOL power in these eyes. Patients with advanced keratoconus may be candidates for keratoplasty with cataract extraction and intraocular lens implantation (IOL) but patients who have had a well-corrected vision with contact lenses or glasses before cataract may not require corneal surgery[6] For these people, the accurate IOL power calculation is a challenge, while determining the correct IOL power plays an important role in achieving acceptable visual results and optimal refractive and in patients satisfaction after cataract surgery. Many computerized videokeratography, keratometry and biometry devices estimate the total dioptric power of the cornea in terms of diopter by determining the radius of the anterior corneal curvature and by the use of an indicator called corneal refractive index or keratometric index (1.3375)[9]. This study aims to calculate the refractive index of such corneas in moderate and severe stages of the disease For this purpose, we simulated eyes, which had been under cataract surgery, and their corneas diagnosed with KCN or PMD. We plan to find out the effect of calculating the total corneal power in determining the more accurate IOL power

Objectives

Methods

Results

Conclusion