Treatment of Irregular Astigmatism with a Broad Beam Excimer Laser

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Abstract
Four basic types of irregular astigmatism are described: central elevation, central flat area, eccentric elevation, and eccentric flat area. The importance of the Munnerlyn formula is shown for the treatment of irregular astigmatism. A new diagnostic entity is described, the steep/flat ratio, modeled on the inferior/superior ratio described previously in keratoconus. Calculation of the steep/flat ratio is described using the cross sectional view of videokeratography, leading to specific treatments for the four types of irregular astigmatism. Surgical technique using the VISX Star excimer laser for repeated laser in situ keratomileusis (LASIK) is described. Case studies are given for each of the forms of irregular astigmatism showing improved topographic appearance and indicating treatment parameters. In each case, improvement of both uncorrected and spectacle-corrected visual acuity is demonstrated. Irregular astigmatism is an important complication of refractive surgery. Four basic forms of irregular astigmatism can be treated with a broad beam excimer laser.

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