A prototype erodible mask delivery system for the excimer laser

Area of Science:

• Ophthalmology
• Laser Surgery
• Biomaterials

Background:

• The argon-fluoride 193-nm excimer laser is a key tool in refractive surgery.
• Developing effective delivery systems for laser ablation is crucial for precise correction of refractive errors.
• Erodible masks offer a potential method for controlling laser ablation patterns.

Purpose of the Study:

• To develop and evaluate an erodible mask delivery system for 193-nm excimer laser ablation.
• To assess the system's efficacy in correcting myopia and hyperopia in a rabbit model.
• To compare corneal healing and clarity post-ablation with the mask versus a diaphragm system.

Main Methods:

• Polymethylmethacrylate masks were fabricated for myopia and hyperopia corrections (2.5 and 5 diopters).
• Excimer laser ablations were performed on 30 rabbit eyes using the mask and a control diaphragm.
• Eyes were monitored for 134 days with regular clinical and retinoscopic examinations.

Main Results:

• Myopic ablations with the mask yielded stable corrections, though higher powers resulted in undercorrection.
• Hyperopic mask ablations led to paradoxical myopic shifts, attributed to the lack of a transition zone.
• Mask-ablated corneas showed reduced sub-epithelial haze compared to diaphragm-ablated corneas.
• Histopathology revealed epithelial hyperplasia and subepithelial new collagen in all ablated eyes.

Conclusions:

• Erodible masks are feasible for myopic ablations, requiring further calibration.
• The current mask design was unsuccessful for hyperopic corrections.
• Mask-ablated corneas may achieve greater clarity due to a potentially smoother ablation surface.
• Epithelial hyperplasia appears to be the primary driver of refractive change regression in this rabbit model.