ESCRS - FP16.03 - Accuracy Of Preoperative Predicted Percentage Of Tissue Altered In Myopic Femto-Lasik Surgery Using Optical Low-Coherence Reflectometry

Accuracy Of Preoperative Predicted Percentage Of Tissue Altered In Myopic Femto-Lasik Surgery Using Optical Low-Coherence Reflectometry

Published 2024 - 42nd Congress of the ESCRS

Reference: FP16.03 | Type: Free paper | DOI: 10.82333/srcm-2j82

Authors: Arturo Chayet* 1

1Ophthalmology,Codet Vision Institute,Tijuana,Mexico

Purpose

To determine the reliability of the percentage of tissue altered (PTA) calculation Using Optical Low-Coherence Reflectometry (Ex500) by comparing the preoperative predicted PTA to the intraoperative and postoperative PTA actually achieved in myopic Femto-LASIK. 

Setting

Codet Vision Institute, Tijauna, Mexico

Methods

Prospective Cohort study of 50 eyes that underwent Femto-Lasik Surgery for correction of moderate to high myopia at CODET Vision Institute from December 2023 - January 2024. The femtosecond laser was programmed to cut LASIK flaps at a depth of 80, 85 and 90um. Optical low-coherence reflectometry (EX500) was used to measure central corneal thickness prior to lifting the flap and the residual stromal bed immediately after excimer ablation. The predicted PTA value was calculated based on the planned flap thickness and the predicted ablation depth and compared with the actual achieved postoperative PTA intra operative and postoperative at one week.

Results

Mean CCT before surgery had no difference between Pentacam and EX500 (p=0.072). Predicted ablation depth with munnerlyn formula had a mean of 55.85 (+/-19.65) and with EX500 65 (+/-17.83) (p=0.02). The ablation depth measured by EX500 77.55 (+/-22.22) was statistically significant compared with the predicted ablation by EX500 and Munnerlyn formula (p=<0.001). The mean difference between the predicted ablation measured by EX500 and archived ablation was -12.55 (+/-7.4). The predicted PTA (Ex500) was 26.96% (+/-3.78) and the achieved PTA was 30.07% (+/-4.5) (p=001) with a mean difference of 3.11% (+/-2.04) underestimated by the predicted formulas.

Conclusions

There was a difference between the preoperative predicted PTA (EX500) and the actual achieved PTA value. The mean difference was 3%, clinically it could affect patients with borderline PTA as in high myopes. Preoperative refractive surgery planning should consider lowering preoperative PTA limits in this case.