Excimer laser ablated cornea observed by atomic force microscopy

The modifications induced by laser ablation on corneal stroma were investigated using atomic force microscopy (AFM). Excimer laser photorefractive keratectomy (PRK) was performed in 10 albino rabbit's corneas after epithelial removal. Ablation of 40 and 80 pm, which corresponds to 03 and 06 diopters for the human eye, was performed on their right eye using an autonomous flying spot 193 nm excimer laser. Lamellar keratectomy with a microkeratome was performed to 10 left eye's corneas to serve as control. All specimens were fixed in glutaraldehyde buffered solution. The observation of treated surfaces was performed in balanced salt solution. The AFM imaging showed the rough appearance and the fine structure of the surface in the treated areas at magnification between x10000 and x100000. The appearance of the surface after lamellar keratectomy consisted of more or less organized fibrils and granular material. The laser treated surfaces were smoother, consisting mainly of a pseudomembrane. Collagen fibrils and proteoglycans were observed in both cases. Details of the fibrillar arrangement, diameter and D-axial periodicity could be distinguished. Minimal preparation permits a high magnification evaluation of the corneal surface in condition closer to normal compared to the condition of specimens prepared for conventional scanning microscopy, AFM represents a new promising mode for the study of laser ablated tissues.