Axial length and pharmacologic pupillary dilation in highly myopic patients.

Purpose: To determine how high myopia impacts pharmacological pupillary dilation, and to evaluate the relationship between the extent of pharmacologic pupillary dilation and axial length.

Methods: Patients were grouped into high myopes, defined as one or both eyes having a refractive error greater than - 6 diopters, and controls (between - 2 and + 2 diopters). Dilation was achieved with 1 drop each of tropicamide 1% and phenylephrine 2.5%. Pupil size was measured at full and dim light prior to dilation, then 15 and 30 min after dilation. Biometry was measured for each patient. Statistical analyses were performed using the Mann-Whitney-Wilcoxon tests, two-sample Welch's t-tests, and linear mixed effect models and generalized estimating equations models accounting for inter-eye correlation.

Results: Forty patients (20 high myopes and 20 controls, 80 eyes total) participated in the study. High myopes had larger pupils at baseline and achieved significantly greater pupillary size (7.08 mm, 95% CI: 6.97 to 7.19 mm) than controls (6.23 mm, 95% CI: 5.94 to 6.52 mm) after 30 min of dilation (P < .0005). Fully dilated pupil size at 30 min was significantly correlated with both refractive error (r =  - 0.57, P < .0005) and axial length (r = 0.47, P < .0005). Generalized estimating equations and linear mixed effect models identified other predictive variables of pupil size after dilation including age and white-to-white diameter.

Conclusions: Highly myopic patients dilate to a larger pupillary size compared to other patients. Predicting dilation based on extent of myopia could facilitate intraocular surgery planning and reduce clinic wait times for myopic patients.