Stephen Taylor


Excimer laser is currently used for experimental reshaping of the front surface of the cornea in the correction of myopic refractive error (photorefractive keratectomy, PRK) and in conditions of corneal irregularity (phototherapeutic keratectomy, corneal smoothing, PTK). Both PRK and PTK are in FDA clinical trials, but are more readily available outside the USA. These techniques have achieved reasonable success in spite of early reports that deeper ablation procedures can cause a lack of corneal clarity (haze) or a less accurate and regressive result. This is a study of how a differing depth of excimer tissue removal affects the smoothness of the ablation zone of the rabbit cornea. Dutch belted rabbits were anesthetized with IM ketamine-xylazine, their corneas were de epithelialized with a knife and they were immediately sacrificed by pentabarbital overdose. A 4.5 mm circular ablation beam was delivered to each denuded area but the beam was masked by a steel blade in order to create variable ablation depths corresponding to 0.0 u, 12.5 u, and 62.5 u. The eyes were fixed in-situ by topical and anterior chamber application of glutaraldehyde and the corneae were excised after 5 minutes, placed in glutaraldehyde for standard EM processing. The corneae were whole mounted and examined by Scanning Electron Microscopy (SEM). The resultant micrographs demonstrate clearly that there is increasing irregularity of the ablation surface as a function of depth. This appeared largely due to the inhomogeneities of the anterior stroma (rabbit cornea is without a discernable Bowman's layer) which is known to be layered by alternately directed collagen fibrils. The more prominent irregularity of the deeper ablation may also be related to the tendency of the excimer to perpetuate irregularities in a surface unless special steps are taken remove them. The presence of a less regular surface for deeper ablations may be a contributing factor to the increased corneal haze noted by other


Year: 1992

Program Number: Poster 30

Author Affiliation: n/a

Co-Authors: Chris Fields, Felix Barker

Co-Author Affiliation: n/a

Room: Great Hall