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Excimer laser ablation rate and corneal hydration
P J Dougherty1, K L Wellish, R K Maloney
1Jules Stein Eye Institute, Los Angeles, CA 90024-7003.
American Journal of Ophthalmology
|August 15, 1994
Summary
Corneal hydration significantly impacts excimer laser ablation rates. Minimizing dehydration during photorefractive keratectomy is crucial for accurate myopia correction and predictable outcomes.
Area of Science:
- Ophthalmology
- Biomedical Engineering
- Laser Surgery
Background:
- Excimer laser photorefractive keratectomy (PRK) involves removing corneal epithelium, initiating dehydration.
- Corneal hydration levels may influence the excimer laser ablation rate, potentially affecting refractive correction accuracy.
Purpose of the Study:
- To investigate the effect of corneal hydration on excimer laser ablation rates in bovine eyes.
- To determine how hydration changes influence both hydrated tissue and dry component ablation rates.
Main Methods:
- Bovine corneoscleral rims were hydrated using varying dextran solutions.
- Laser ablation was performed on corneal buttons, and mass removed was measured.
- Hydrated tissue and dry component ablation rates were calculated based on mass loss.
Main Results:
- The hydrated tissue ablation rate increased with corneal hydration (5.6 µg/cm²/pulse per unit increase).
- Conversely, the dry component ablation rate decreased linearly with increased hydration (-0.82 µg/cm²/pulse per unit increase).
- Physiologic hydration showed a hydrated tissue ablation rate of 0.40 µm/pulse.
Conclusions:
- The dry component ablation rate, which increases with corneal dehydration, is critical for refractive outcomes in PRK.
- Significant corneal dehydration before ablation may lead to myopic overcorrection.
- Techniques minimizing hydration changes are recommended for maximizing PRK predictability.