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—In our study, we noted that for eyes with a cycloplegic refraction in the range of -2.00 to -2.50 D, the average uncorrected manifest visual acuity of eyes undergoing RK (20/63) was better than the average visual acuity of unoperated-on eyes (20/125). We agree with Dr Applegate and Mr Jones that one possible explanation for this observation is that we measured cycloplegic refraction with the pupil dilated and uncorrected visual acuity with the pupil in its normal state. The possible effect of pupil size was discussed at length in the section entitled "Diameter of the Pupil."As stated in the article, after RK, the paracentral cornea flattens less than the central cornea, beginning at the edge of the central clear zone. This may produce a slight increase in refractive myopia when the pupil is dilated. Therefore, after RK, the uncorrected visual acuity may be better than that suggested
Santos VR, Waring GO, Lynn MJ, Holladay JT, Sperduto RD. Relationship Between Refractive Error and Visual Acuity in the PERK Study-Reply. Arch Ophthalmol. 1987;105(11):1479. doi:10.1001/archopht.1987.01060110024011