The differential pupillary response to 2.5% phenylephrine in patients taking tamsulosin

Purpose: To determine if a pharmacological test could be developed to determine iris dilator dysfunction in patients taking tamsulosin. Methods: Patients taking tamsulosin and controls were recruited from the Urology and Ophthalmology clinics at the Montefiore Medical Center. The patient's right eye (OD) was dilated with phenylephrine hydrochloride 2.5% and tropicamide 1%. The patient's left eye (OS) was dilated with tropicamide 1% alone. Forty minutes after dilation, pupillary diameter was measured in both eyes. Results: Thirty-eight tamsulosin subjects and 43 controls met the inclusion criteria for the study. The tamsulosin-treated patients dilated less with phenylephrine than controls (0.61±0.4 vs. 1.10±0.45μmm, respectively P<0.001). Receiver operating characteristic curves comparing maximal pupillary dilation versus differential pupillary dilation in tamsulosin patients relative to controls shows a greater area under the curve for differential dilation (0.8 vs. 0.6, respectively). A correlation between smooth muscle dysfunction and length of time on tamsulosin was observed. Patients using tamsulosin for <1 month had an average OD-OS difference of 0.85±0.5μmm. Patients who were on tamsulosin for >1 month had an average OD-OS difference of 0.52±0.32μmm (P<0.01, Mann-Whitney). Conclusion: Patients treated with tamsulosin demonstrated a significantly decreased iris dilatory response to the selective adrenergic effects of phenylephrine compared to controls. Additionally, it appears that longer duration of exposure to tamsulosin increases the likelihood of dilator dysfunction.