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K. Holliday, C.E. Campbell; Observations on Early Stage Healing Following a Wavefront–Guided PRK Refractive Treatment . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4392.
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Purpose: This paper reports early changes in the surface shape of two eyes of the same subject following wavefront–guided PRK treatments for refractive error. The asymmetry of epithelial recovery and the interaction between the uneven epithelium and the tear film were closely observed. Methods: Measurements are reported for corneal topography using a Humphrey Atlas device, wavefront aberrometry using a VISX WaveScan device, and corneal and epithelial thickness using a Haag–Streit Pachymeter. Corneal topography measurements were begun four days after treatment, a few hours after the bandage contact lens was removed, and were continued several times per week for seven weeks. The data gathered by the topographer were analyzed by purpose–written MatLab programs that determined the corneal shape changes both on a day–by–day basis and relative to the intended post–treatment shape. During these examinations the mire images were used to observe post–blink changes in the tear film as the initially formed tear film flowed to even out underlying epithelial layer irregularities. Wavefront aberrometry and corneal and epithelial thickness measurements were used as complements to the corneal topography measurements to construct an overall picture of the shape of the surface of the eye. Changes on the order of microns could be observed so that day–to–day variation of the surface shape could be distinguished, especially during the very early stages of recovery. Results: The tear film can replicate a very irregular underlying surface, but between blinks the film changes to smooth its own surface. The epithelial layer initially thickens preferentially in the nasal and temporal periphery so that astigmatism is induced. Differential epithelial thickening took place primarily in a brief period between the 6th and 8th days post–operatively. The differential peripheral thickening was of the order of 3–4 µm. Conclusions: By combining corneal topography, wavefront aberrometry and pachymetry the early stage recovery of the surface of the eye following PRK surgery can be followed with high resolution allowing day–to–day changes to be mapped and the dynamics of the tear film to be studied.
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