Corneal Dystrophy by George Jones          The globe of the eye is made of five layers with the cornea being the transparent front portion. It is also the most sensitive structure in the body due to the density of nerves.  The cornea is transparent due 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 are a group of rare disorders which usually affect both eyes. They may be present at birth, but more frequently occur during adolescence and progress gradually throughout life. Some forms are mild, while others can be severe.
        This group of disorders tends to be genetic in nature and the causes of most corneal dystrophies will lie in individual genetic make-up. Although age of onset, symptoms and progression differ in the various dystrophies, most cases of corneal dystrophy fall into three  types, classified by their inheritance pattern and appearance. These are Dominant Granular Dystrophies, Recessive Macular Dystrophy and Dominant Lattice-like Dystrophies.

    a. Dominant granular dystrophy usually starts while the pup is still young.  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 adulthood, opacities are visible to the  naked eye.

    b. Recessive macular dystrophy usually starts during young adult time period 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.

    c. Dominant lattice-like dystrophy can develop in infancy but more usually during the reproductive peak of life. This is seen as a cobweb of fine lines which develop into a lattice-like pattern. From your dog's golden years 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.

Genetic Inheritance

        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.

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. Crystalline corneal opacities (CCO), less accurately referred to as corneal dystrophy, affect the cornea, the foremost transparent portion of the outer coat of the eyeball. The defect produces a gray haze and/or needle-like crystals within the cornea, spreading across its surface and, in some cases, obscuring the vision of the dog. As is the case in bilateral cataracts, both eyes are affected, although not necessarily at the same time or to the same degree.

Recessive Macular Dystrophy is a severe dystrophy which may cause considerable damage by mid-life.

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.

Treatment

In some conditions corneal grafting offers a good prospect of visual improvement.

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