The relationship of visual acuity, refractive error, and pupil size after radial keratotomy
J. T. Holladay, M. J. Lynn, G. O. Waring 3rd, M. Gemmill, G. C. Keehn and B. Fielding
Hermann Eye Center, Department of Ophthalmology, University of Texas Medical School, Houston 77030.
To better define the relationship between residual refractive error,
uncorrected visual acuity, and pupil diameter, we compared 42 eyes that had
an eight-incision radial keratotomy according to the Prospective Evaluation
of Radial Keratotomy Study protocol with 42 matched control eyes. The
parameters measured were best corrected visual acuity, uncorrected visual
acuity, and the change in cycloplegic refraction with enlarging pupil
diameter. The best corrected visual acuity was 20/16 in both the radial
keratotomy and control groups, but the variability (SD) was higher in the
radial keratotomy group. The average uncorrected visual acuity was 0.35
(35%) better in the radial keratotomy group, but the variability was 1.77
times higher. Change in refraction with dilation occurred in 9% of the
controls and 36% of the radial keratotomy patients, indicating a
significant difference (P = .002). The change in refraction with dilation
in the eyes with radial keratotomy was almost equally split between a
hyperopic change (17%) and a myopic change (18%), which was much different
than in the control eyes, only 2% of which changed in a hyperopic direction
and 7% in a myopic direction. The radial keratotomy patients with a myopic
change had the best uncorrected visual acuity, indicating that positive
spherical aberration yielded the best aspherical surface for uncorrected
visual acuity.
