What is Corneal Dystrophy? The globe of the eye is made of five layers and the cornea is the transparent front portion. It is also the most sensitive structure in the body because of the density of nerves.

The cornea owes its transparency to the presence of a regular lattice structure of collagen fibres. Anything which affects this regularity results in loss of the transparency which is essential for good corneal function and health.

Corneal dystrophies form a group of rare disorders which usually affect both eyes. They may be present at birth, but more frequently develop during adolescence and progress gradually throughout life. Some forms are mild, others severe.

What causes the Corneal Dystrophies? Corneal dystrophies are mostly genetic which means the run in families. They have different inheritance patterns and the implications of this need to be discussed with you ophthalmologist.

What are the effects of the three main types of Corneal Dystrophy? Although age of onset, symptoms and progression differ in the various dystrophies, most cases of corneal dystrophy fall into three well defined clinical and genetic types, classified by their inheritance pattern and appearance. These are Dominant Granular Dystrophies, Recessive Macular Dystrophy and Dominant Lattice-like Dystrophies.

Dominant granular dystrophy usually starts at around 5 years of age. This can be seen as small white dots in the centre of the cornea or may take the form of lines radiating from the centre. These signs can increase in size and number and by 50 years of age, opacities are visible to the naked eye.

Recessive macular dystrophy usually starts in the first decade of life and appears as a thin superficial corneal veil with isolated opacities when seen with a slit lamp. It is the least common type of dystrophy. Acute, short lived, attacks may be experienced and there is increasing haziness of the central part of the cornea and increasing isolated opacities. Dominant lattice-like dystrophy can develop in infancy but more usually during the second decade of life. This is seen as a cobweb of fine lines that develop into a lattice-like pattern. By 40 years of age onwards, the centre of the cornea can become irregular with ill-defined opacity.

Although in some people the pattern of progress is less severe, acute attacks are experienced which can contribute to relatively early onset of sight loss. Among other types Fingerprint Dystrophy, Fuch's Dystrophy, Meesman Dystrophy and Reis-Buckler Dystrophy are most encountered.

What are the genetic implications? Dominant single gene diseases result from one of a pair of matched autosomal genes having a disease and the other being normal. With each pregnancy there is a 1 in 2 chance of the disease appearing in the offspring.

Recessive single gene disease requires both parents to carry the condition and this results in a 1 in 4 inheritance risk in each pregnancy. Only siblings within a single generation are affected, unless members of that generation create offspring with another carrier of the specific gene.

It is valuable to seek genetic advice on all conditions which have an hereditary cause in order to identify how this may affect individual family members. Information about local genetic services will be available from your General Practitioner or the hospital eye specialist.

What is the prognosis? Although there are many more forms of corneal dystrophy, essentially there are three inherited classical varieties and the progress and likely outcome varies with each. Dominant Granular dystrophies are usually mild and may be unnoticed by those with the condition. In some cases sight is not affected even in later years.

Recessive Macular Dystrophy is a severe dystrophy which may cause considerable damage by 30 years of age. Dominant Lattice-like Dystrophies can be either mild or severe and from middle-age these may cause acute attacks, capable of causing serious sight loss.

Is there any treatment available? In some conditions corneal grafting offers a good prospect of visual improvement.

Other RNIB services Low Vision Services Low Vision Services exist to optimise vision by the use of techniques, aids, lighting and general information. The eye specialist will be able to advise you on the nearest Low Vision Clinic within the Hospital Eye Service where a loan service will be available on a variety of sight enhancing equipment.

Employment and Rehabilitation RNIB has specialist departments to advise on these subjects. Discussion of your situation and needs, prior to any decision about leaving or changing work, might help you identify useful technology or retraining possibilities. Support from an experienced and knowledgeable independent advisor can be helpful in deciding whether to retain current employment with additional support from technology and other services or make a fresh start.

What's next? If you've recently been diagnosed with a sight problem or even if you've been living with sight loss for some time, read our practical advice to continue living confidently. If you need more information contact RNIB’s Helpline on 0845 766 9999 / helpline@rnib.org.uk - calls are charged at local rates.

Other organisations? Although some groups exist for individual types of dystrophy, RNIB is not aware of a specialist group offering support and information for families with Corneal Dystrophies.

RNIB Education Service is happy to discuss the ways in which children with sight problems can achieve their potential and advise on local educational and other services - email them at E&ELondon@rnib.org.uk.

Local voluntary organisations for blind and partially sighted people will be able to offer a range of support and other services and local information. Mobility training and other rehabilitative courses should be offered by your community social services at the time of registration. Copy of the registration document, BD8, should be sent to Social Services.

 Written by Karl Varkey