Eye Care Blog

Tests for Glaucoma

When examining you an ophthalmologist will test eye-pressure through the simple expedient of placing his fingers on your closed eyelids. The experienced physician will know immediately whether the pressure is unusually high, but even so he is unlikely to be able to distinguish, using this technique, between more than four grades: namely soft, normal, suspicious and high. Accurate measurement requires instruments. Such instruments have to touch the cornea, which is therefore suitably anaesthetized beforehand, using a special kind of drop. Several types of local anaesthetic drop exist, e.g. amethocaine, pentocaine and xylocaine. One instrument blows a puff of air on to the cornea and then measures the degree of corneal flattening that results. This does not require a local anaesthetic. Other kinds of test attempt to induce the pressure of the eye to rise (e.g. by using a dark room, making the patient read something, or infusing drops that make the eyes dilate). The purpose is to measure the pressure under conditions that may occur regularly in your life. For example, the dark room may help simulate what happens to your eyes while you are asleep, while the use of drops enables the doctor to examine the angle of the eye, to see whether it is unusually occluded by the iris. Such tests may be termed challenge tests. But of equal importance are tests that establish whether the optic nerve is healthy. These consist in looking at the disc, or head, of the optic nerve with instruments that magnify the retina. The sensitivity of the retina can also be assessed by various light-threshold tests, especially using colours. You look into a black box as the practitioner operates a filter that allows only tiny pinpricks of progressively less faint light to flash up before you. This plots any defect in your whole field of vision. It is usually necessary to conduct two or three different investigations. The results of these are then analysed together and, with knowledge of your general health and your family background, a diagnosis can be made. In some instances, where the eye-pressure fluctuates significantly during the course of a day, it is necessary to repeat the tests several times at different intervals before a realistic evaluation can be made.

Thus the diagnosis of chronic simple glaucoma, at least in its early stages, is not easy. It is an insidious affliction in more ways than one. There is, however, another kind of glaucoma, called acute congestive glaucoma, which is much more readily identified. Its onset is marked by a sudden, severe pain, redness in the eye and high cloudation of the cornea. In addition, the pupil may become dilated, and the eye-pressure is likely to be abnormally high. Unless you are treated almost immediately you will rapidly become generally ill, because of the persistence of the pain. You will develop severe stomach cramps, may vomit, and perhaps even collapse. Immediate treatment of such cases is essential, and if you do not respond to intensive outpatient care you may require admission to hospital for surgery.

This type of acute glaucoma can be preceded by sub-acute attacks, which you may pass off as some kind of normal eyestrain and therefore not bring it to the attention of a doctor. Before the acute attack commences, the visual fields and eye- pressure may have been perfectly normal; hut unless the suddenly exaggerated pressure can be swiftly controlled a substantial and permanent loss of vision is likely to occur.

There are many different reasons why eye-pressure may suddenly increase. Inflammation inside the eye can cause the angle between cornea and iris to become closed. The same is true of internal tumours and post-operational infections. Even cataract, where it causes the inner crystal lens to swell, can lead to a relatively sudden increase in eye-pressure.

Treatment for Glaucoma

Treatment depends upon the type of glaucoma experienced by the patient. Diagnosis is therefore all-important, and there are some ophthalmologists who have specialized in this one area because of its public health importance.

Chronic simple glaucoma is best treated conservatively with drugs (eye-drops). Only if these fail is surgery used. On the other hand, a lifetime’s dependence on a drug is not desirable, and therefore some surgeons operate early. If the operation is successful no further medication will be required. Thus the management of glaucoma varies from practitioner to practitioner. Where surgery is not or has not become essential, the age of the patient may well be a consideration. If the patient is very old it seems wiser, on several grounds, to continue with a medical treatment.

Most drugs used in the care of glaucoma have specific effects, but these cannot always be easily analysed, and sometimes there are side-effects. One of the least expensive and best behaved drugs is Pilocarpine. This can be used as often as four or five times a day, and even in the night. It works by constricting the pupil and thus opening the angle between cornea and iris. Possibly it has other beneficial effects upon the drainage of fluids from the eye, but these are only partly understood. Timoptol (timolol), on the other hand, is a drug that operates by suppressing fluid formation. Possibly it blocks the automatic nerve supply to the blood vessels in the ciliary region. However, if it is used with patients who are either asthmatic or who have constrictive vascular heart disease, there can be some serious complications. As with all potent drugs, one has to accept that side-effects are inevitable. Unfortunately these may not always be apparent from laboratory and animal experiments, and even well-tested drugs are sometimes used by humans for several months or years before their defects become measurable.

Pilocarpine and Timoptol, which are available in various concentrations, are the two most commonly used drugs in the treatment of glaucoma. But, apart from drugs (of which there are several), laser rays have also been used more recently to open up the angle of the eye, and/or make tiny holes in the iris to enable the fluid to move freely from the middle to the front of the eye without blocking the angle. The use of laser outpatient treatment has attracted a great deal of publicity, but while it certainly has its adherents inside the profession, the long-term effects are still being studied. Conventional surgery can also do this, as well as create new filtering channels so that high eye- pressure will rapidly stabilize to normal. In general, however, the treatment of glaucoma is as problematic as is its diagnosis, and requires- highly qualified and experienced practitioners to obtain the best results.

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