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R Ou, BJ Glasgow, EL Shaw; Does a 250um Residual Stromal Bed Forestall Keratectasia After LASIK? . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1716.
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Purpose: To study 3 eyes with keratectasia after LASIK. Methods: Three eyes with keratectasia after LASIK are described clinically, and the eyes requiring penetrating keratoplasty are examined with light and transmission electron microscopy. Our findings are compared to the 44 previously published eyes with keratectasia after LASIK. Results: Three eyes of two patients displayed keratectasia after LASIK. Residual stromal bed thicknesses were calculated to be 210, 213, and 261 µm, falling within the range of reported eyes (113 to 353 µm). In previously reported eyes with keratectasia, 61% had residual stromal beds greater than 250 µm after LASIK, considered an acceptable thickness to avoid keratectasia after LASIK. Topographical analysis prior to LASIK did not uncover forme fruste keratoconus in our patients; 62% of reported eyes showed evidence of forme fruste keratoconus or keratoconus. One of our patients displayed bilateral keratectasia. This finding has been reported in 55% of published keratectasia patients that received bilateral LASIK. Each eye in our series received a single LASIK treatment, while 43% of published eyes received multiple treatments. Two eyes in our series underwent penetrating keratoplasies compared to 46% of published eyes. Light and transmission electron microscopy of the two corneal specimens revealed minimal focal scarring near the flap, but corneal lamellae were generally intact. The residual stromal beds measured 161 and 207 µm in the histological specimens. There was a slight increase in keratocytes between the flap and stromal bed. Individual lamellae varied in thickness near the site of the flap. Conclusion: Keratectasia may be a vision threatening complication after LASIK that often requires penetrating keratoplasty. Histopathology confirms that residual stromal thinning after this procedure in our cases. Reported cases of histology suggests that keratectasia results from reduced overall lamellar strength and is difficult to predict from the thickness of the residual bed immediately after LASIK. Our study questions the clinical guideline that a residual stromal bed thickness of 250 µm will prevent keratectasia after LASIK.
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