The cornea and eye surface

What does the cornea do?

The cornea is the clear layer at the front of the eye. It bends light as it enters so you can see sharply. A thin film of tears covers its surface. If the cornea or this film is disturbed, sight blurs even when the lens and retina are healthy.

Dry eye

Dry eye happens when too few tears are made, tears evaporate too fast or they do not cover the eye well. A gritty feeling, stinging, redness, light sensitivity and blurred vision are common.

Being over 50, wearing contact lenses, autoimmune conditions such as lupus and Sjögren syndrome, some medicines and long hours at a screen raise the risk.

These help:

• Keeping away from smoke, wind and direct air conditioning
• Adding moisture to indoor air
• Taking regular screen breaks
• Wearing wraparound sunglasses outdoors
• Getting enough sleep

Treatment starts with artificial tears and, depending on severity and cause, may move to gels, ointments, prescription drops or plugs in the tear ducts.

Keratoconus

In keratoconus the cornea thins and bulges into a cone. It usually begins in the late teens or early twenties, often affects both eyes and progresses gradually over years.

Blur, straight lines that look bent, light sensitivity and a prescription that keeps changing are the signs. The exact cause is unknown, but it is linked with eye allergy, frequent rubbing and family history. Rubbing further weakens a thin cornea, so try to avoid it.

Treatment depends on severity:

• Glasses or soft lenses in mild cases
• Firmer, specialised lenses later on
• Corneal cross-linking with drops and ultraviolet light to toughen the tissue
• Implants placed in the cornea to reshape it
• Corneal transplant in severe cases

Corneal infection and inflammation (keratitis)

Infections linked to contact lenses are the most common cause. Eye pain, blurred vision, redness, watering and light sensitivity are the signs. If you wear lenses and have these, take the lens out at once and call an eye doctor the same day. An untreated infection can scar and reduce sight.

Injury, scars and transplant

Minor scratches usually heal on their own, but deeper injuries can leave a scar. When the damage cannot be repaired, a corneal transplant replaces it with healthy donor tissue.

When should it be checked urgently?

Severe eye pain, a change in vision, intense redness or watering, an object stuck in the eye and any serious injury need an eye doctor or the emergency department at once.