PURPOSE. Orthokeratology is the programmed application of contact lenses to temporarily reduce myopia and corneal toricity. Improved techniques and better patient selection exist as interest in orthokeratology has grown. Because of the inherent optical consequences of modifying the central cornea in orthokeratology, we hypothesize that visual acuity and objective refraction will change in conditions when the patient's pupil is large, such as physiologically large pupils or low light conditions.
METHOD. Eight orthokeratology patients in retainer lens phase were used in the study. Each patient was dilated with 1%Tropicamide and 2.5% phenylephrine and allowed to sit for 20 minutes. Auto refraction and Bailey-Lovie high and low contrast visual acuities were measured. The patient was fit with a black annular 4.5mm size fixed pupil hydrogel contact lens and measurements repeated for each eye. A five patient control group was tested using the same regimen.
RESULTS. Results were analyzed using the Wilcoxon signed rank confidence interval Wilcoxon signed rank test. In the experimental group the median improvement in high contrasat visual acuity from the dilated eye to the 4.5mm fixed pupil for the right eye was 0.0150 logMAR(p=0.022); for low contrast acuity 0.0150 logMAR(p=0.036). The median improvement for high and low contrast acuity for the left eye was 0.0100 logMAR(p=0.059). The mean change in autorefraction from the dilated to the 4.5mm fixed pupil was +1.123D(p=0.014) for the right eye and 0.78D(p=0.022) for the left eye.
CONCLUSIONS. A statistically significant median increase in myopia of approximately one diopter was found in the experimental group with large pupils. There was a statistically significant median decrease of approximately one line of high and low contrast visual acuity in the experimental group with large pupils. Similar trends were found in the control group with large pupils, but statistical significance was not found.