Certified Paraoptometric (CPO) Practice Exam 2026

Phenylephrine is an alpha-adrenergic agonist commonly used in ophthalmology for its ability to dilate the pupil and potentially alter intraocular pressure (IOP). The effects of phenylephrine on IOP typically last for several hours, and the duration can be influenced by various factors including the concentration used and the individual patient’s response.

The most accurate understanding is that phenylephrine usually affects intraocular pressure for around 3 to 5 hours. During this time, it can lead to a temporary decrease in IOP due to changes in the drainage of aqueous humor. The choice indicating 3-5 hours aligns with clinical observations regarding its pharmacodynamics in terms of IOP management and monitoring following administration.

Other durations such as 1-2 hours, 5-6 hours, and 6-8 hours do not reflect the typical duration of effect observed in practice, as they exceed or fall short of the commonly recognized timeframe for its action on intraocular pressure.