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M. J. Belliveau, P. Gooi, S. Brownstein, W. B. Jackson, G. Mintsioulis, S. Dravida, E. Dare, R. Buhrmann, M. Griffith; Histological and Biological Comparison of Corneal Epithelium Removal by Mechanical and Chemical Methods. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3348.
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Epi-photorefractive keratectomy (Epi-PRK) and advanced surface ablation (ASA) are forms of refractive surgery in which the corneal epithelium is removed prior to treatment. In ASA, alcohol is used to loosen the epithelium, while in Epi-PRK it is lifted mechanically with an epithelial delaminator. In patients undergoing phototherapeutic keratectomy for recurrent erosion syndrome (PTK-RES), the epithelium is removed mechanically using a microhoe. The cleavage plane of these methods has not been well established and this information may have implications related to clinical outcomes, including post-operative pain and haze. This study characterized the epithelial cleavage plane of these methods using light microscopy. We also investigated the viability and proliferative ability of the basal cell layer after removal using both histological and biological tests.
Prospective case series on subjects whose corneal epithelium was removed using an epithelial delaminator (n=10), microhoe (n=10), or application of 20% alcohol for 20 seconds (n=10).Histological studies with PAS were used to characterize the proportion of cleavage at six levels for each epithelial flap, and the mean calculated for each of the three study groups.Basal epithelial cell proliferation was measured by staining with MIB-1 and PCNA antibodies. Viability testing was performed using SYTO 10 & EthD-2 stains. Corneas with no evidence of epithelial disease (n=10), obtained through routine penetrating keratoplasty, were used as a control for proliferation and viability testing. The proportion of proliferating/viable cells was determined for each specimen and the mean calculated for each of the four groups.
The mean proportion of cleavage at the level of the basement membrane was 44% in Epi-PRK, 12% in ASA, and 84% in PTK-RES cases. The mean proportion of basal cells showing positivity for MIB-1 and PCNA, respectively, was 1.7% and 17.8% in Epi-PRK, 2.5% and 17.6% in ASA, 2.5% and 4.7% in RES cases, and 4.9% and 8.1% in control corneas. In Epi-PRK 90% of the basal cells were viable and in ASA 84% were viable. Viability results for PTK-RES and control corneas are pending.
Our results indicate that the mechanical methods of corneal epithelial removal (Epi-PRK and PTK-RES) have a higher proportion of cleavage at the basement membrane compared to the chemical method (ASA). There is no significant difference in viability or proliferation of the basal epithelial cells in the methods studied.
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