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Biomechanics spur complications in laser vision correction
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BOSTON — Contrary to prevailing opinion, refractive shifts in laser vision correction are driven by biomechanical factors and are reversible, a speaker said here.
"The single most potent biomechanical force in the cornea is a tiny negative interstitial fluid pressure," Brian R. Will, MD, said at the American Society of Cataract and Refractive Surgery meeting. "Alteration of local control of [interstitial fluid pressures] induces tissue swelling and redistributes tissue tension."
Biomechanical factors also contribute to complications and inflammatory conditions such as diffuse lamellar keratitis, central toxic keratopathy and epithelial ingrowth after laser correction, Dr. Will said.
Inflammatory cytokines generate negative interstitial fluid pressures from the corneal center to the periphery. As a result, limbal fluid moves centrally and causes swelling of the midperipheral cornea. Thickening of tissue in this region creates biomechanical tension and central tissue compression that result in thinning of the central residual stromal bed, Dr. Will said.
Altered pressure, tissue tension and tissue compliance result in a hyperopic shift and spherical aberration in myopic corrections, as well as myopic shifts in hyperopic corrections, he said.
In addition, diffuse lamellar keratitis results when inflammatory cytokines dominate pressure control and lead to a disparity between the flap and residual stromal bed, Dr. Will said.
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