Are there any signs or symptoms of simple glaucoma?

In the earlier stages, no symptoms are experienced though mild headaches and eye aches may occur. Often there is a sudden unexplainable increase in the number of reading glasses, which would immediately alert an eye doctor that all is not well.

Sometimes, gaps in vision are noticed. For example, one patient commented that when he reads the licence plate of a car from behind, the tail light seems to disappear.

Other common complaints are: "Recently I began to need more light to read than I did previously" and "I can't see in the dark as well as before".

To be frank, unless the intra-ocular tension is checked as a regular part of every eye examination at regular yearly intervals, symptoms of simple glaucoma are so vague that they can be easily missed.

Symptoms in the later stage when the tension has already gone up considerably, are:

(a) The classical coloured haloes around lights.

(b) Foggy vision.

(c) Pain and occasional redness—the pain is typically in the temples but it may be in the forehead and may even radiate backward down the neck.

(d) Short blackouts of vision—a few seconds to a few minutes.

(e) The eyeball feels hard rather than soft and resilient.

At this stage, glaucoma is usually detected because symptoms are obvious. Unfortunately by this time a certain loss of vision is almost definite. Still if it is controlled well, further deterioration of vision can be prevented.

How is glaucoma checked by a doctor? What tests does he carry out?

(1) Intra-ocular tension: This is the most important test for glaucoma. The normal pressure measured by the smaller Schiotz instrument is 16.5 (12.6) mm and by the newer aplanation is 15.4 (12.5) mm (Becker & Schaffer).

Upto 21 mm is taken as normal pressure but over 24 mm is taken as clear glaucoma.

(2) Visual fields: Since glaucoma causes pressure and thus loss of function of certain nerve fibres in the retina, there are typical losses of segments of vision in the visual field (for short, doctors talk of "field loss"). This can be detected by checking peripheral fields (the full outer extreme limits of vision) and central fields (magnified central 30° of vision).

Field studies are a simple way of assessing the damage done by glaucoma and for checking how effective the treatment is in controlling glaucoma.

(3) Retina examination through an ophthalmoscope: To directly see how much damage the pressure has done. In glaucoma, due to continuous exposure to high pressure in the eyeball, the centre of the optic nerve as it emerges from the eyeball (seen as a round zone and hence called the optic disc) tends to develop a hollow or an excavation termed as an optic cup. The depth and size of the cup shows the quantum of damage done to the eye.

How are the glaucoma fields checked?

(A) Peripheral fields

The instrument is termed the perimeter. There are two types, the older, object moving type and the new projection type. The instrument evaluates the extent of the outermost limits of the field. In glaucoma narrowing of the field or missing segments are seen.

Peripheral fields are also used to evaluate any retinal changes, like tumours or a retinal detachment. It is easy specially with the new light projection type to exactly plot the extent of the affection. It, also helps in evaluating the success of the treatment.

(B) Central fields

The central 30 degrees of vision in essence covers the most important part of the retina, the optic disc area and the macula. The optic disc is where the nerve fibres of the retina form a bundle and pass out of the eyeball as the optic nerve. Seen end-on, it resembles a disc and hence the name. The macula is the area of the clearest vision in the retina.

The central fields are evaluated by one of two methods: the first is the tangent screen method. A grey or black felt screen with degrees stitched on it is kept a metre away from the sitting patient. A wand is moved in front and the blind spot (vide infra) is plotted, as well as any non-seeing areas. These areas result from damage to particular nerve fibre bundles due to the raised eye pressure.

The newer rapid technique for scanning these glaucomatous central field defects is by using electronically controlled phase spots of light. The patient has only to say how many spots he sees and the entire central field analysis can be done in a few moments. This instrument, the Friedman visual field, is very accurate and gives reproducible readings with great rapidity.

Dustin Flores

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