Which agent should be used with caution in patients with narrow-angle glaucoma due to the risk of increasing intraocular pressure?

• A. Timolol
• B. Latanoprost
• C. Phenylephrine
• D. Acyclovir

Answer: (C)

Dilation of the pupil can worsen narrow-angle glaucoma because it narrows the angle where fluid drains from the eye, raising the pressure. Phenylephrine is a potent alpha-1 agonist that causes significant pupil dilation (mydriasis). In eyes with narrow angles, this dilation can push the iris forward and narrow or close the drainage angle, leading to a rise in intraocular pressure and potentially triggering an acute angle-closure attack.

The other options don’t have this effect. Timolol reduces aqueous humor production, helping lower intraocular pressure. Latanoprost increases outflow of aqueous humor, also lowering pressure. Acyclovir is an antiviral with no direct impact on intraocular pressure. If dilation is needed in someone with narrow angles, it should be used with caution and under close monitoring, or alternatives should be considered.