Corneal Disorders

What the cornea does

The cornea is a clear, dome-shaped tissue about half a millimeter thick. It provides about two-thirds of the eye's focusing power and acts as a barrier against germs and dust. It has no blood vessels, which keeps it clear, but it has one of the densest nerve supplies in the body. That is why even a small scratch hurts so much.

It has five layers. The outer epithelium heals quickly. The thick middle stroma gives strength and clarity. The inner endothelium is a single layer of cells that pump water out to keep the cornea clear. Endothelial cells do not regenerate, so damage there can cause lasting cloudiness.

Types of corneal disorders

Keratitis and corneal ulcers

Keratitis means inflammation of the cornea. Contact lenses are the biggest risk factor for bacterial and Acanthamoeba infections, especially sleeping or swimming in them. Herpes simplex keratitis can recur and is a leading infectious cause of corneal blindness in developed countries. An ulcer can scar the cornea within days, so it needs prompt care.

Fuchs endothelial dystrophy

This inherited condition usually shows in people over 50 and is more common in women. Endothelial cells gradually fail, so fluid builds up in the cornea. Vision is typically blurry on waking and clears as the day goes on, because fluid evaporates from the surface. Later, painful blisters can form.

Keratoconus

The cornea thins and bulges into a cone, usually starting in the teens or twenties. It causes increasing nearsightedness, astigmatism, ghosting and glare. Eye rubbing and allergies are linked to progression.

Other dystrophies and degenerations

Epithelial basement membrane (map-dot-fingerprint) dystrophy can cause recurrent painful erosions on waking. Lattice and granular dystrophies leave deposits that cloud vision over decades. Band keratopathy is calcium deposited across the cornea, often with chronic eye inflammation or high blood calcium.

Symptoms of corneal disease

• Eye pain, from mild grittiness to severe pain.
• A feeling that something is in the eye.
• Redness, especially around the colored part of the eye.
• Light sensitivity (photophobia).
• Watering.
• Blurred, hazy or distorted vision, glare and halos around lights.
• A visible white or gray spot on the clear part of the eye.

Pain, light sensitivity and reduced vision together point to the cornea or the inside of the eye rather than simple conjunctivitis, which usually leaves vision normal.

How corneal disorders are diagnosed

An eye doctor examines the cornea under a slit-lamp microscope. A drop of orange fluorescein dye glows green under blue light wherever the surface is broken. Other tests include:

• Corneal topography or tomography: maps the shape and thickness, key for keratoconus.
• Pachymetry: measures thickness, used in Fuchs dystrophy.
• Specular microscopy: counts endothelial cells.
• Corneal scraping and culture: identifies the germ in a serious infection.
• Corneal sensation testing: checks for nerve damage.

Treatment

Treatment depends on the cause:

• Lubricating drops and gels for dryness and surface damage.
• Antibiotic, antiviral or antifungal drops, often hourly at first for serious infections.
• Bandage contact lenses or amniotic membrane to help healing.
• Hypertonic saline (5% sodium chloride) drops to draw fluid out in early Fuchs dystrophy.
• Corneal cross-linking: riboflavin drops activated by UV light stiffen the cornea and can halt keratoconus.
• Rigid or scleral contact lenses to restore clear vision with an irregular cornea.
• Laser (phototherapeutic keratectomy) to remove surface scars or deposits.
• Corneal transplant (keratoplasty): replacing all layers (penetrating keratoplasty) or only the diseased layer, such as DMEK for Fuchs dystrophy. Corneal transplants are among the most successful tissue transplants.

Avoid steroid eye drops unless prescribed after an eye exam. They can make herpes and fungal infections much worse.

Prevention

• Wash hands before handling lenses, never sleep or swim in them unless designed for it, and replace cases regularly.
• Wear eye protection for grinding, hammering, yard work and chemicals.
• Avoid rubbing your eyes, especially if you have allergies or keratoconus.
• Treat dry eye and eyelid problems early.
• Wear UV-blocking sunglasses outdoors.

Frequently asked questions

What are the most common corneal diseases?

The most common are corneal abrasions, dry eye, and keratitis (infection or inflammation), especially in contact lens wearers. Among longer-term conditions, Fuchs endothelial dystrophy is the most frequent dystrophy in older adults, and keratoconus is the commonest shape disorder in young people.

What is keratopathy?

Keratopathy is a general term for any non-inflammatory disease of the cornea. Doctors add a word to describe the type, for example exposure keratopathy from incomplete eyelid closure, band keratopathy from calcium deposits, or bullous keratopathy from fluid blisters when the inner cell layer fails.

Can a damaged cornea repair itself?

The outer layer usually heals within 1 to 3 days after a small scratch. Deeper damage to the middle layer heals with a scar, which can blur vision. The inner endothelial cells do not regrow, so damage there is permanent and may eventually need a transplant.

What is corneal dystrophy?

A corneal dystrophy is an inherited condition in which abnormal material builds up or cells fail in one layer of the cornea. Dystrophies usually affect both eyes, progress slowly, and are not caused by infection or injury. Fuchs dystrophy is the most common type.

When should I see a doctor for a corneal problem?

See an eye doctor the same day for a painful red eye with light sensitivity or blurred vision, especially if you wear contact lenses or have had an injury. Book a routine appointment for gradual vision changes, morning blurriness or recurring grittiness.