A dry eye is an eye without enough tears. Confusingly, the eye can often feel watery rather than dry, and also have a sensation of burning or grittiness. This deficiency gives rise to chronic irritation, which can cause damage to the cornea and in severe cases corneal scarring.

There may be episodes of excessive tearing or wateriness, mucous discharge or blurred vision.

This condition can arise from a number of things, for example:

A pterygium is a fleshy growth that invades the cornea (the clear front window of the eye). It is an abnormal process in which the conjunctiva (a membrane that covers the white of the eye) grows into the cornea. Pterygia may be small or grow large enough to interfere with vision. It commonly occurs on the inner corner of the eye.

Pterygium occurs more often in people who spend a great deal of time outdoors, especially in sunny climates. Long-term exposure to sunlight, especially ultra-violet (UV) rays, and chronic eye irritation from dry; dusty conditions seem to play an important causal role.

When a pterygium becomes red and irritated, topical eye-drops or ointment may be used to help reduce the inflammation. If the pterygium is large enough to threaten sight, is growing or is unsightly, it can be removed surgically.

Despite proper surgical removal, the pterygium may return, particularly in young people. Conjunctival graft to the site is used to decrease recurrence. Topical medications are sometimes also used to help prevent recurrences. Protecting the eyes from excessive ultraviolet light with proper sunglasses and avoiding dry, dusty conditions may also help.

Keratoconus is a condition that results in progressive thinning of the cornea. The cornea is the clear, front window of the eye, which focuses light onto the retina. The cornea is normally smooth and dome-shaped. However, in keratoconus, the cornea becomes very thin, irregular, and starts to protrude like a cone. This causes blurred vision that is often not correctable with glasses. Keratoconus usually involves both eyes, however one eye may be more advanced than the other.

The cause of keratoconus is still not known. Genetics plays a role, since approximately 10% of people with keratoconus also have a family member with the condition. Certain ethnic groups are also more predisposed to developing keratoconus.

Treatment often depends on the severity of the condition, and presence of progression. During early stages, vision can be corrected with glasses. As the condition progresses, rigid contact lenses may need to be worn.

Progression, if present, can in most cases be stopped with collagen cross-linking treatment, a day procedure that strengthens and stiffens the cornea. However, cross-linking is ineffective in advanced keratoconus, so early detection is important.

Patients who have keratoconus should refrain from rubbing their eyes, as this can aggravate the corneal thinning, and make symptoms worse.

When good vision is no longer possible with contact lenses, a corneal transplant may be recommended. This operation is only necessary in about 10-20% of patients with keratoconus. Of all conditions requiring corneal transplants, keratoconus has the best prognosis for clear vision.