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Errors of residual stromal thickness estimation in LASIK
Huey-Chuan Cheng1, Yen-Tung Chen, Shu-I Yeh
1Department of Ophthalmology, Mackay Memorial Hospital, Taipei, Taiwan.
Summary
Estimating residual stromal thickness after LASIK is often inaccurate due to variations in corneal thickness, flap creation, and ablation depth. Intraoperative measurements are recommended for patients with borderline corneal thickness to prevent complications like ectasia.
Area of Science:
- Ophthalmology
- Refractive Surgery
- Corneal Biomechanics
Background:
- Accurate estimation of residual stromal thickness (RST) is critical for safe and effective LASIK surgery.
- Variability in pachymetry, flap thickness, and ablation depth can lead to significant errors in RST prediction.
- Iatrogenic ectasia is a serious complication associated with insufficient stromal thickness post-LASIK.
Purpose of the Study:
- To investigate the inaccuracy and variability in estimating residual stromal thickness (RST) after LASIK.
- To analyze the impact of corneal thickness, flap thickness, and ablation depth measurements on RST prediction accuracy.
Main Methods:
- Corneal thickness was measured preoperatively using ultrasound pachymetry and slit-scanning elevation topography in 73 eyes.
- LASIK was performed, and flap thickness and ablation depth (expected vs. achieved) were calculated.
- Residual stromal thickness estimation error was analyzed based on these measurements.
Main Results:
- Preoperative corneal thickness measurements varied between ultrasound pachymetry and topography (mean difference up to 30 microm).
- Microkeratome flap thickness averaged 139.58 microm.
- Predicted ablation depth differed from achieved depth by 20% or more in 30.14% of patients, and by 10-19.99% in 37%.
Conclusions:
- Imprecision in microkeratome cuts, preoperative pachymetry, and laser ablation depth significantly impacts RST prediction accuracy.
- Intraoperative pachymetry and maintaining an RST above 250 microm are recommended, especially for patients with borderline corneal thickness.
- These measures are crucial for minimizing the risk of iatrogenic ectasia.
