Purpose: To compare the efficacy of phenylephrine 2.5% versus 10% on pupillary dilation, and also compare their side-effects.
Method: Patients at the Eye Clinic Srinagarind Hospital were randomized into two groups. Patients in group 1 received 1% tropicamide and 10% phenylephrine, whereas those in group 2 received 1% tropicamide and 2.5% phenylephrine. Pupil diameter, blood pressure and heart rate were measured before and after eyedrop instillation.
Results: Five hundred and sixty four patients were randomized into 293 patients (group 1) and 271 patients
(group 2), using simple random sampling method. Mean pupil diameters before instillation in group 1 were 4.43 + 1.13 mm in the right eye and 4.31 + 0.95 mm in the left eye, whereas those in group 2 were 4.45 + 1.0 mm in the right eye and 4.32 + 0.92 mm in the left eye. After the instillation, the mean pupil diameters in group 1 were 7.58 + 0.96 mm in the right eye and 7.60 + 1.03 mm in the left eye, whereas those in group 2 were 7.17 + 1.04 mm in the right eye and 7.07 + 1.06 mm in the left eye. The difference was statistically significant (P < 0.05). There was no significant difference in mean systolic and diastolic blood pressure after instillation between the two groups. However, the mean heart rate after instillation in group 1 was greater than the value in group 2 with statistically significant difference.
Conclusion: Pupillary dilation with 1% tropicamide and 10% phenylephrine is more effective than 1% tropicamide and 2.5% phenylephrine with statistically significant difference. After single dose instillation, there was no significant difference in the mean blood pressure between the two groups.

Keywords: Phenylephrine, Pupillary dilation, Side effect