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D.G. Dawson, I. Schmack, B.E. McCarey, H.E. Grossniklaus, H.F. Edelhauser; Cohesive Tensile Strength of Human Laser in situ Keratomileusis Wounds With Histologic and Ultrastructural Correlation . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2167.
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Purpose:The purpose of this study was to measure the cohesive tensile strength of human LASIK corneal wounds. Histology and ultrastructural correlations from the separated and intact portions of the specimens were evaluated to help better understand the biomechanical results. Methods:Twenty–one human corneosceral specimens from 11 eyebank donors with previous LASIK surgery were obtained from U.S. eye banks. Four–mm limbus–to–limbus corneoscleral strips were cut and dissected by manual lamellar dissection to expose the LASIK interface wound. Using a motorized pulling device with an attached force transducer, the force required to separate the wound in LASIK corneas was measured (grams/mm). Intact and torn portions of the specimen were processed for histologic and ultrastructural evaluations. Eleven normal control corneoscleral specimens from 7 eyebank donors served as controls. Results:The mean tensile strength averaged 2.5% (0.75 +/– 0.33 gram/mm) of normal (30.21 +/– 3.03 grams/mm) in wound regions (central and paracentral) that contained a hypocellular primitive stromal scar and 24.9% (7.52 +/– 4.30 grams/mm) of normal in the flap wound margin, which contained a hypercellular fibrotic stromal scar. Although the hypocellular primitive scar demonstrated no gain in strength over time, the peak tensile strength of the hypercellular fibrotic scar gradually increased until maximum values were reached by 3.5 year post–operatively; averaging 28.0% (8.46 +/– 4.56 grams/mm) of normal. There was no significant difference in wound strength between mechanical and laser microkeratome LASIK cases. Histologic and ultrastructural correlations demonstrated that wound margins with persistent epithelial ingrowth were on average one third the strength of those without epithelial ingrowth. Conclusions: Human corneal stroma typically heals in a limited and incomplete fashion that results in a very weak, transparent hypocellular primitive scar. The LASIK wound margin is different in that epithelial–stromal interactions appear to augment the normal corneal stromal wound healing response typically resulting in a 10–fold stronger and 30% more hazy hypercellular fibrotic scar.
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