Effects of Diagnostic Mydriasis with Tropicamide and Phenylephrine on Intraocular Pressure

Purpose: To determine the effects of diagnostic mydriasis using 1% tropicamide and 2.5% phenylephrine on the intraocular pressure of patients attending the Eye Clinic of University of Port Harcourt Teaching Hospital. Methods: This was an interventional ‘within-patient’ comparative hospital-based study conducted over 3 months, in which the right eyes of 137 subjects requiring diagnostic mydriasis received 1% tropicamide and 2.5% phenylephrine. The left eyes served as control. Results: There were 137 study participants: 86 males (62.8%) and 51 females (37.2%). The mean age of participants was 44.87±15.94 years. The baseline IOPs were 12.34±3mmHg for the Right Eye (RE) and 12.09±2.64mmHg for the Left Eye (LE). The mean post dilatation IOP at 30, 45, 60, 90 and 120 minutes in the RE were higher than baseline. The maximum mean post dilatation IOP in the RE was 13.75±2.99mmHg and this occurred at 45 minutes. In the control undilated LE, the mean post dilatation IOPs were lower than baseline at all the follow up periods except at 45 minutes where it was slightly higher (12.11±2.87mmHg). These differences in mean IOP change were statistically significant (p<0.05). At all the follow-up periods, 8.8%-14.6% of participant’s right eyes had large IOP elevations (>5mmHg but <10mmHg). Multiple linear regression analysis showed that pre dilatation IOPs were positively correlated to post dilatation IOPs. Conclusion: There is need to recheck IOP post dilatation preferably at 45 minutes in all patients who have had diagnostic mydriasis to prevent damage to the optic nerve. Diagnostic mydriasis could safely be done using small concentrations of tropicamide and phenylephrine.