The cornea is the transparent front portion of the eye. It needs to be clear and have a normal curved shape to focus light accurately and provide good vision. 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, although the severity may be asymmetric. 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 result from genetic alterations, and in many cases run in families. They have different inheritance patterns depending on the condition.

What are the effects 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.

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.

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. The first indication of the condition may be recurrent corneal erosion syndrome , giving episodes of painful and photophobic eyes, before vision is affected. By 40 years of age onwards, the centre of the cornea can become irregular with ill-defined opacity and the vision is usually reduced.

Macular dystrophy is the least common type. It usually starts in the first decade of life and appears as a thin superficial corneal haze with isolated opacities when seen with a slit lamp. Central corneal haze progresses and usually significantly affects vision from the 20s onwards.

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.

Is there any treatment available?

Treatment is available for recurrent corneal erosion, which may be a feature of lattice or granular dystrophies, with topical lubrication, contact lenses, laser or surgery.

Poor vision may be treated by laser surgery (phototherapeutic keratectomy with the excimer laser) in granular and occasionally lattice dystrophy, or by lamellar or penetrating keratoplasty (corneal graft).