Strabismus Measurements in Adults Before and After Pupil Dilation

Purpose To determine the effect of dilating drops on strabismus measurements in adults. Design Prospective cohort study. Methods Patients aged 18 and older with strabismus underwent a standard evaluation of ocular motility, stereopsis, and ocular alignment with alternate prism cover test by a certified orthoptist. After pupil dilation with 2.5% phenylephrine and 1% tropicamide, ocular alignment was remeasured in primary gaze at 6 meters, at 1/3 meter, and at 1/3 meter with a +3.00 by a second certified orthoptist, masked to the previous measurements. The primary outcome was the mean difference in the angle of horizontal and vertical deviations after dilation in prism diopters. Results A total of 55 patients were enrolled with a variety of diagnoses. For horizontal measurements the mean change was 0.54 prism diopters at 6 meters (95% confidence interval [CI] −0.36 to 1.43, P = .24), 1.67 prism diopters at 1/3 meter (95% CI −0.19 to 3.54, P = .08), and −0.05 prism diopters at 1/3 meter with a +3.00 add (95% CI −1.65 to 1.56, P = .95). The mean change in vertical deviation was 0.18 prism diopters at 6 meters (95% CI −0.19 to 0.56, P = .34), 0.57 prism diopters at 1/3 meter (95% CI 0–1.15, P = .05), and 0.47 prism diopters at 1/3 meter with a +3.00 add (95% CI −0.23 to 1.17, P = .18). Conclusions Pupil dilation does not meaningfully affect vertical or horizontal strabismus measurements in adults. Mild variability at near in younger patients is eliminated with the use of a +3.00 add.