The three cardinal signs are:

1. Raised intraocular pressure.

2. Cupping of the optic disc.

3. Visual field loss.

The intraocular pressure creeps up gradually to 30-35mmHg, and it is this gradual rise that accounts for the lack of symptoms. Such a rise in intraocular pressure impairs the circulation of the optic disc, and the nerve fibres in this region become ischaemic. The combined effect of raised intraocular pressure and atrophy of nerve fibres results in gradual excavation of the physiological cup, and it is extremely useful to be able to identify this effect of raised intraocular pressure at an early stage. Figure 12.1 shows an optic disc undergoing various stages of pathological cupping. In the first instance, the central physiological cup becomes enlarged, with its long axis arranged vertically. Notching of the neuroretinal rim of the optic disc tissue, especially in the inferotemporal and superotemporal region, is common. The edge of the optic disc cup corresponds to the bend in the blood vessels as they cross the disc surface. In some eyes the area of pallor can correspond to the cup, while in others the cup is larger than

Figure 12.1. The effect of glaucoma on the optic disc. CO

Figure 12.1. The effect of glaucoma on the optic disc. CO

the area of pallor. It is particularly useful to observe the way in which the vessels enter and leave the nerve head (Figure 12.2). A flame-shaped haemorrhage at the disc margin can be seen. Localised loss of retinal nerve fibres can be observed, especially with a red-free light. Diagnostic instrumentation, such as the GDx nerve fibre layer analyser, is capable of measuring the thickness of the retinal nerve fibre layer in microns, and offers an adjunctive objective measure for diagnosing and monitoring glaucoma (Figure 12.3).

The changes in the visual field can be deduced from observing the disc and from considering the arrangement of the nerve fibres in the eye. If we gaze fixedly with one eye at a spot on the wall and then move a small piece of paper on the end of a paper clip, or even the end of our index finger, in such a manner as to explore our peripheral field, it is soon possible to locate the blind spot. In the case of the right eye, this is found slightly to the right of the point of fixation because it represents the projected position of a b

Figure 12.2. a Glaucomatous cupping of the disc early cupping; b advanced cupping. CD

Figure 12.3. GDx nerve fibre scan result.

the optic nerve head in the right eye. The blind spot is rounded and about 8-12° lateral to and slightly below the level of fixation. It has already been mentioned that the glaucomatous disc is initially excavated above and below so that the patient with early glaucoma has a blank area in the visual field extending in an arcuate manner from the blind spot above and below fixation. This typical pattern of field loss is known as the arcuate scotoma (Figure 12.4). If the glaucoma remains uncontrolled, this scotoma extends peripherally and centrally. It can be seen that even at this stage the central part of the field could be well preserved and the patient can still be able to read the smallest letters on the Snellen test chart. If the field loss is allowed to progress further, the patient becomes blind.

Figure 12.2. a Glaucomatous cupping of the disc early cupping; b advanced cupping. CD

Figure 12.4. Superior arcuate visual field defect, right eye.

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