Causes of Irregular Astigmatism
Irregular astigmatism may be present before keratorefractive surgery; it may be caused by the surgery; or it may develop postoperatively. Preoperative causes include keratoconus, pellucid marginal degeneration, contact lens warpage, significant dry eye, corneal injury, microbial keratitis, and epithelial basement membrane dystrophy (Fig 7-7). All these conditions should be identified before surgery. Common intraoperative causes include decentered ablations and central islands, and, less commonly, poor laser optics, nonuniform stromal bed hydration, and LASIK flap complications (a thin, torn, irregular, incomplete, or buttonhole flap; folds or striae of the flap; and epithelial defects). Postoperative causes of irregular astigmatism include flap displacement, diffuse lamellar keratitis and its sequelae, flap striae, posterior corneal ectasia, irregular wound healing, dry eye, and flap edema.
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Schallhorn SC, Farjo AA, Huang D, et al. Wavefront-guided LASIK for the correction of primary myopia and astigmatism: a report by the American Academy of Ophthalmology. Ophthalmology. 2008;115(7):12491261.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.