Surface Ultrastructure After Excimer Laser Ablation: Expanding vs Contracting Apertures

Excimer laser corneal ablation (photorefractive keratectomy) for myopia using a diaphragm delivery system was performed on eye bank and animal eyes by either progressively expanding or contracting the iris aperture. Use of an expanding aperture, in which the final ablations cover the entire treatment zone, produced a pseudomembrane over the zone that had few discontinuities. Ultrastructural examination of the corneas ablated using a progressively contracting aperture, however, revealed numerous discontinuities in the surface pseudomembrane. Use of an expanding iris aperture to perform ablations to correct myopia may be preferable as it produces a pseudomembrane with few discontinuities. Clinical studies of surface healing in humans are necessary to determine the clinical relevance of improved continuity of the surface pseudomembrane.