Ocular Infections

Bacterial Conjunctivitis and the Ocular Antibiotic Toolkit

A red, sticky eye is one of the most common reasons a patient walks into a clinic — and one of the most over-treated. Most bacterial conjunctivitis clears on its own within a week or two; the antibiotic drops we reach for often just make everyone feel better about doing something. But hidden inside that same red eye are a handful of causes that are true emergencies — a gonococcal infection that can eat through a cornea in a day, a chlamydial infection that is a leading cause of blindness worldwide, and a contact-lens wearer whose "conjunctivitis" is actually Pseudomonas melting the cornea. The whole skill is knowing which red eye you're looking at, and which ones the drops cannot fix.

Microbial Keratitis: The Sight-Threatening Corneal Infection

A red, painful eye is one of medicine's great false friends. Most of the time it is conjunctivitis — irritating, self-limiting, harmless. But hiding in that same crowd is an infection of a completely different order: an ulcer eating into the cornea itself, the clear window in front of the eye. Miss it, treat it like pink-eye, and within days the infection can scar the exact patch of cornea the patient sees through — leaving a permanent white cloud on the visual axis. Microbial keratitis is not a nuisance. It is an emergency, and the pharmacology that saves the eye looks nothing like the pharmacology of conjunctivitis.

Viral and Fungal Eye Infections: Herpes, Adenovirus and the Moulds

Not every red, painful eye is bacterial — and reaching for the wrong drug can cost the patient their cornea. A branching ulcer that lights up green under the slit lamp is herpes simplex, and the single most dangerous thing you can do is soothe it with a steroid. A filamentary mould seeded by a thorn scratch will shrug off every antibiotic you own. This chapter is about the eye infections antibiotics cannot touch: the viruses you fight with aciclovir and ganciclovir, and the fungi you fight — slowly, stubbornly — with natamycin and voriconazole. The recurring lesson is always the same: name the organism first, and never, ever put a steroid on a dendrite.

Endophthalmitis: Infection Inside the Eye and the Intravitreal Route

Most eye infections sit on the surface — a red conjunctiva, an inflamed lid — and a drop or a tablet reaches them easily. Endophthalmitis is the opposite: bacteria multiplying in the vitreous gel at the very back of the eye, walled off from every drug you would normally reach for. Swallow an antibiotic and the blood–ocular barrier keeps it out. Instil a drop and it never gets past the front of the eye. The pus is inside a sealed chamber, and the only way in is through the wall. That single fact — that the route is the whole treatment — is why endophthalmitis is one of the true blinding emergencies of ophthalmology, and why the needle goes straight into the vitreous.