Corneal Diseases: Keratitis, Ulcers & Transplant Guide

The cornea is the clear dome-shaped window at the front of the eye and provides roughly two-thirds of its focusing power. Keratitis means inflammation of the cornea, most often from infection. A corneal ulcer is an open sore where infection has eaten into the tissue. When the cornea is scarred beyond repair, a corneal transplant replaces it with healthy donor tissue.

Corneal disease matters because the cornea has no blood vessels — it heals slowly and scars easily, and a central scar blocks vision permanently. Bacterial ulcers can perforate the eye within days. Yet corneal transplant is among the most successful transplants in medicine, restoring sight to millions.

Key Concepts

• Bacterial keratitis: the most urgent type. Pseudomonas in contact-lens wearers can destroy the cornea in 24–48 hours. Signs: severe pain, photophobia, white infiltrate, sometimes pus in the anterior chamber (hypopyon). Treated with intensive fortified antibiotic drops, hourly at first.
• Viral keratitis: herpes simplex causes a branching dendritic ulcer seen with fluorescein dye; treated with acyclovir. Steroids must be avoided during active viral infection.
• Fungal keratitis: follows injury with vegetative matter in farm workers; slow, dry, raised ulcer needing antifungal drops like natamycin.
• Acanthamoeba keratitis: parasite infection from lenses rinsed in tap water or worn while swimming; pain far worse than the signs suggest.
• Fluorescein staining: orange dye glowing green under blue light wherever the surface is broken — the standard test revealing ulcers and their size.
• Corneal transplant: penetrating keratoplasty replaces full thickness; DSEK/DMEK replace only the inner endothelial layer and heal faster. Donor corneas come from eye banks.

How It Works

1. Invasion: microbes enter through a scratch, lens micro-trauma or thorn injury; white cells gather into a visible infiltrate.
2. Ulceration: the surface breaks into an open sore staining bright green with fluorescein, showing exact borders.
3. Diagnosis and treatment: a corneal scraping goes for microscopy and culture; broad-spectrum drops start immediately, as often as hourly.
4. Healing or surgery: small ulcers heal with faint scars; large, central or perforated ulcers need transplant to restore clarity.

Worked Example

1. A lens wearer presents with a painful red eye; fluorescein reveals a 3 mm × 4 mm ulcer near the corneal center.
2. Ulcer area ≈ 3 × 4 = 12 mm². The cornea is ~11.5 mm across, so its area ≈ π × 5.75² ≈ 104 mm².
3. The ulcer covers 12 ÷ 104 × 100 ≈ 11.5% of the cornea — moderate in size, but its central position threatens the visual axis.
4. Scraping grows Pseudomonas. She gets hourly fortified antibiotics, stops lens wear, and is reviewed daily; transplant stays in reserve if it worsens.

Common Misconceptions

• Myth: Sleeping in contact lenses occasionally is fine. Fact: overnight wear multiplies infection risk; lenses starve the cornea of oxygen and trap microbes.
• Myth: Red-eye drops fix corneal infection. Fact: they only whiten temporarily while infection spreads; delay risks perforation.
• Myth: Transplant means replacing the whole eye. Fact: only the clear front window is replaced; retina and optic nerve stay untouched.

Real-World Applications

• Eye banks: collect and distribute donor corneas, enabling transplant within days of donation.
• Contact-lens clinics: teach hygiene — no tap water, no overnight wear — preventing most infections.
• Emergency eye care: same-day scraping and hourly drops save eyes that would otherwise perforate.

The cornea is the eye's main focusing window: infections cause ulcers that fluorescein dye reveals, and hourly targeted drops cure most cases. When scarring destroys clarity, corneal transplant — full-thickness or endothelial — is a highly successful operation that gives sight back.