Eye Care Blog

Since the retinal nerves radiate from the cup of the optic nerve (the seat of the blind spot) the loss of retinal function tends to occur in a way that is diagnostic. For example: the group of nerve fibres that tend to be affected first are those that function in arches around the centre of vision. The next group to go are those providing vision in the nasal field (the lateral part of the retina). But it is all too possible for a patient to be unaware of these losses of vision, and because the condition is symptom-free in its early stages and only gradually progressive, diagnosis is often difficult. It has been estimated that between one and two per cent of people over fifty suffer such deterioration. It is even possible for the degeneration to take place without any noticeable changes in eye-pressure, and this has led doctors to speak of a variety of possible causes. Some will say that the fluid channels providing outflow from the eye are degenerate, while others will say that it is the ciliary processes that are at fault, making too much fluid. Yet another explanation is sought in the capillaries surrounding the optic nerve. It is these that are at the root of the problem, say some doctors; it is these that shrivel up first and cause the tissue to decay. In this case, which is probably the truth of the matter, deterioration of the drainage system is only a secondary failure, and takes place because of a breakdown in general nutritional process, which is supplied by the retinal capillaries.

But what causes these changes? What causes glaucoma? Is it genetic? Is the decay built into our genes or is it due to outside factors? Can glaucoma be brought on by the wrong diet, by drugs, or by other environmental factors? Perhaps the answer lies, once more, in a combination of both genes and environment. Some people may be genetically programmed to be vulnerable to certain sorts of environment. This at least would explain why some diets seem to have an adverse effect on some individuals and not on others. Certainly some types of glaucoma recur in the same family (though of course members of one family will tend to react the same way to an environmental etiology).

Equipment has been designed to measure accurately the pressure in the eye and to test the field of vision. There are also tests to measure the flow of aqueous fluid from the eye when stress is put upon the eye-pressure system. But even if an early diagnosis is made, treatment is not necessarily effective, and the final outcome can be almost complete loss of the fields of vision except at the centre of sight. Affected individuals can still see clearly in the distance, and can read clearly, but they are unable to move about with any confidence, because they cannot see anything that is not directly in front of them. They have lost their peripheral vision, and in acute cases they may even have difficulty in following a line of print. Such a condition is called `tunnel vision‘, and is accounted a form of blindness, a fact little _understood or appreciated by the general public.

The onset of this kind of glaucoma is very slow and many patients do not know that they are affected. Sometimes the first noticeable indication is a loss of colour hue discrimination. It occurs most frequently in post-industrial ‘civilized’ communities, but this may simply be because in such communities the average life-span is longer, or because, in technological societies, people are more likely to damage their eyes by too much close-work. Even so, senile or elderly glaucoma has a relatively low incidence. About two per cent of the population over fifty will have eye-pressure above the normal, but only in perhaps 0.2 per cent (one in every five hundred) of the age group will specific treatment be sought or required.

Because it tends mostly to affect people over fifty there are possible connections with senile peripheral blood vessel degeneration, which affects other sensitive tissues in the body. There are, however, other causes and types of the glaucomous condition, of raised intra-ocular pressure. Some of these are too rare to be worth describing here, but others are not.

Infantile glaucoma occurs when the baby is born with an abnormal outflow of fluid from the eye. This often means that the angle of the eye has developed without adequate outflow channels. At birth the tissues of the eye are soft, and as the eye-pressure increases the eye becomes bigger. This can be a painful condition, and the baby may be distressed and unhappy. The cornea of the infant suffering glaucoma appears especially large and is sometimes cloudy. The eyes, also unnaturally big, will look red. There will be quiet periods, without pain, but diagnosis is essential. The condition can be treated either with drugs (eye-drops) or with surgery, opening up new channels for drainage of the fluid from the eye. If treatment is not provided, however, the eye may become very severely affected, and treatment at a later stage will be pointless.

There is also a condition of juvenile glaucoma, equally rare, but, like the infantile form, capable of leading to a loss of vision. It is generally considered a late development of the infantile condition.

Some doctors consider minor forms of glaucoma to be present in children who subsequently become myopic. Early high eye- fluid pressure, in this view, causes the eye to elongate and thus cause short-sightedness. Increased pressure owing to excessive close-work is often cited as the classic explanation of myopia, but in fact this has never been substantiated clinically.

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