To the Editor.
—In radial keratotomy (RK), the central surgery-free zone and the peripheral surgical area of the cornea can have different optical properties.1 Since the eye is a variable aperture (pupil) optical system, the impact of differences in optical properties (in particular, refractive error) on retinal image quality will vary with pupil size. As a result, there are at least three interrelated optical implications that need to be considered in evaluating patients following refractive surgery. All three implications are based on the assumption that the peripheral optics of the eye undergoing RK can be different than the central optics. Based on this relatively safe assumption (1) the optimal correction may vary as a function of pupil size; (2) for any given correction (associated with a particular pupil size), visual acuity may vary as a function of pupil size; and (3) the optimal visual performance and correction will be
Applegate RA, Jones DH. Relationship Between Refractive Error and Visual Acuity in the PERK Study. Arch Ophthalmol. 1987;105(11):1478-1479. doi:10.1001/archopht.1987.01060110024010