Glaucoma / Ophthalmic Agents

The front of the eye is continually bathed by a fluid called aqueous humor, made behind the iris and drained out through a mesh at the angle of the eye. When production and drainage fall out of balance, intraocular pressure (IOP) rises. In glaucoma, that elevated pressure slowly damages the optic nerve, causing irreversible, painless loss of peripheral vision — a leading cause of blindness.

Every glaucoma drug works by lowering IOP, and there are only two levers to pull: make less aqueous humor, or drain more of it out. Different drug classes pull one lever or the other. The goal is a pressure low enough to halt optic-nerve damage — vision already lost cannot be recovered, so the therapy is about prevention of further loss.

Latanoprost and the other prostaglandin analogs (the "-prost" drops) are the first-line treatment. They lower IOP by increasing uveoscleral outflow — opening an alternate drainage route so more fluid leaves the eye. They are effective, dosed once daily at night, and have very few systemic effects, which is why they displaced β-blockers as the go-to drug.

Their signature effects are local and cosmetic: a gradual, often permanent brown pigmentation of the iris (especially in mixed-color eyes), darkening and lengthening of the eyelashes, and conjunctival redness (hyperemia). Patients must be told about the eye-color change up front — it is harmless but can be striking and irreversible.

Timolol is a topical β-blocker that lowers IOP by decreasing aqueous humor production. Here is the crucial nursing concept: an eye drop does not stay in the eye. It drains through the nasolacrimal (tear) duct into the nose and is absorbed into the bloodstream — so timolol can produce the same systemic β-blockade as an oral beta-blocker: bradycardia, hypotension, and bronchospasm. That makes it dangerous in asthma/COPD, bradycardia, and heart block, and it can mask hypoglycemia in diabetics.

The fix is a simple, high-yield technique: after instilling the drop, close the eye and apply gentle pressure over the inner corner (punctal/nasolacrimal occlusion) for ~1–2 minutes. This keeps the drug on the eye and blocks its drainage into the systemic circulation. The other classes each pull their own lever — α2-agonists (brimonidine) reduce production and increase outflow, carbonic anhydrase inhibitors (dorzolamide; oral acetazolamide) reduce production, and cholinergics (pilocarpine) constrict the pupil to increase outflow — cross-linking to the Beta-Blockers, Autonomic cholinergics, and diuretic content elsewhere in the course.