Acuities through annular and central pupils after radial keratotomy.
The corneal radius of curvature after radial keratotomy (RK) increases centrally in the surgery-free area while remaining relatively unchanged paracentrally and peripherally in the surgical areas. These corneal topography changes suggest that the imaging properties of the cornea should vary with the area of the cornea allowed to participate in image formation. To test this hypothesis visual acuities were measured both through a central and an annular pupil for normals and RK patients as a function of time after surgery. Annular acuities were decreased significantly after RK and remained decreased over time. Best corrected central acuity increased as a function of time after surgery, becoming significantly better than presurgery acuities but not as good as normals with similar low refractive corrections. Clinical implications include: (1) variations in visual performance (e.g., acuity, contrast sensitivity, glare) and optical quality measures (e.g., refraction, higher-order aberrations) as a function of pupil size; (2) use of a large a surgery-free area as possible; (3) careful centering of the surgery-free area on the natural pupil; (4) new contact lens designs for correcting RK patients' residual refractive error; and (5) counseling patients in general, and patients with naturally large pupils in particular, concerning possible variation in visual function with pupil size. In summary, this study indicates that postsurgery RK paracentral/peripheral corneal optics experience a loss in optical quality as compared to either normal eyes with a low refractive correction or the same eye before surgery.
Department of Ophthalmology, University of Texas Health Science Center, San Antonio.
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Applegate
D000328:Adult; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007646:Keratotomy, Radial; D008297:Male; D008875:Middle Aged; D011680:Pupil / Q000502:physiology*; D054140:Refractive Surgical Procedures; D014792:Visual Acuity / Q000502:physiology*