Evaluating the Accuracy of Refractive Lenticule Created by a New Femtosecond Laser in Glass

Abstract

Purpose : A new femtosecond laser system, which is currently in development, will be used to perform corneal lenticule extraction for refractive surgery. OCT measurements were used to evaluate the accuracy of refractive lenticule created by the new femtosecond laser system.

Methods : For refractive lenticule cutting in glass (Fuse silicon, index 1.452 at 850nm wavelength), 10 glass samples were used for creating the myopic lenticules (range from -1.00D to -10.00D with adding 30um flat in each lens), and 10 glass samples were used for creating the hyperopic lenticules (ranging from 1.00D to 10.00D with adding 30um flat in each lens). After the refractive lenticule was created in each glass sample with 80nJ laser energy, RTVue XR Avanti OCT system (Optovue Inc., 5µm axial resolution at 850nm wavelength) was used to measure the 6-mm pachymetry scan that consisted of 8 meridian B-scan images. Then the OCT B-scan images were exported from the OCT device and an image processing algorithm was used for automatic segmentation to detect the lenticule’s anterior and poster cuttings lines. Each lenticule’s pachymetry map was reconstructed and the lenticule central thickness was calculated. Zernike polynormal up to 6^th order was reconstructed in a 6-mm pupil from the lenticule’s pachmetry map and the refractive error was calculated from the 2^nd order of Zernike polynormal. The achieved refractive power was compared with target manifest refraction over a 4mm pupil at 12.5mm vertex distance.

Results : Lenticule cutting lines created by the new femtosecond laser system in glass were visible in the OCT B-scan images. For myopic lenticule cuts, the difference between the achieved central thickness and the target central thickness was 1.64±0.43µm (range: +083 to +2.39µm), and the linear regression between the manifest myopic power and the achieved myopic power has a slope of 0.9949 and r-square of 0.9998. For hyperopic lenticule cuts, the difference between the achieved central thickness and the target lenticule central thickness was 3.07±0.29µm (range: +2.63 to+3.54µm), and the linear regression between the manifest hyperopic power and the achieved hyperopic power had with slope of 0.9885 and r-square of 0.9996.

Conclusions : Results demonstrated that this new femtosecond laser produced accurate myopic and hyperopic lenticules in glass. The achieved lenticule central thickness and sphere power agreed with the target.

This is a 2020 ARVO Annual Meeting abstract.