Diseases of the conjunctiva and cornea

There are a large number of conditions that can affect the conjunctiva and cornea.

Corneal abnormalities

These include -:

• Corneal dystrophies in which there is opacification (clouding) of the cornea which may be associated with thickening, ulceration and cyst formation. There are a large number of corneal dystrophies, which are usually inherited. Each type has different clinical features and prognosis.
• Scarring due to forceps delivery during birth.
• Keratoconus (conical distortion of the cornea) is usually bilateral but is unilateral (affecting one eye) in 10% of cases. It is more common in people with allergic conditions and is associated with other ocular and systemic disorders, for example congenital cataracts and Downs syndrome. It results in astigmatism (blurred vision due to light not focussed regularly onto the retina) and myopia (short sightedness). It usually presents between 10 and 20 years of age, but can be earlier. Progression of the disease is variable and asymmetrical (not even). It tends to worsen slowly for up to 10 years and then stop but there may be episodic deterioration over a longer period. Very rarely there may be sudden onset of visual deterioration caused by fluid accumulation in the cornea, which may result in corneal scarring. In the early stages, treatment of the refractive error may be achieved with spectacles but hard contact lenses are better at correcting the astigmatism (blurred vision due to light not focussed regularly onto the retina). Later on, surgery (corneal grafting) may be necessary with rejection being rare and the visual prognosis is usually good.

Prognosis: Any corneal condition that leads to scarring will lead to visual impairment with central opacities causing severe visual impairment. Keratoconus has a good outlook with treatment by spectacles, contact lenses and if necessary a corneal transplant.

Infections

There are a wide range of organisms that can cause infections of the conjunctiva and cornea. Some organisms, if inadequately treated can cause inflammation and scarring of the cornea resulting in visual impairment. This is more common in developing countries. Such organisms include -:

• Chlamydia trachomatis (a sexually transmitted micro-organism) producing trachoma (chronic inflammation of the mucous membranes of the eyes),
• Adenovirus infection (a type of virus that can cause conjunctivitis),
• Herpes simplex virus infection (an acute viral disease marked by groups of small blisters on the skin)
• Measles
• Gonorrhoea; and
• Certain bacteria, for example pseudomonas 9a type of bacteria).

Conjunctivitis beginning within the first month of life is called Ophthalmia Neonatorum and usually results from the eye being exposed to micro organisms in the birth canal during birth. The commonest cause in developed countries is chlamydial infection but other causes include herpes simplex and gonorrhoea. This is an ophthalmic emergency.

Treatment varies according to the infecting organism and the severity of the infection. Parents must also be seen and treated if necessary.

Prognosis: Most infections detected early and treated well have a good outlook. Severe infections, if undetected and untreated, can lead to corneal ulcer and impaired vision.