The most obvious physical sign is the semi-dilated fixed pupil. The iris and the constricting sphincter muscle of the pupil are damaged by the raised intraocular pressure. The pupil is not able to constrict and after a day or two the iris becomes depigmented, taking on the grey atrophic colour that gave glaucoma its name. Prompt and effective treatment should prevent any damage to the iris. The eye is red and a pink frill of engorged deeper capillaries is seen around the corneal margin; this important sign, as opposed to conjunctival inflammation, is known as ciliary injection. Corneal oedema can usually be detected without optical aids by observing the lack of luster in the eye and any attempts to assess the hardness of the eye by
palpating it through the eyelids will elicit another sign, that of tenderness of the globe. The visual acuity might be reduced to "hand movements" in a severe attack. There are two rather subtle signs that often persist permanently after the acute attack has been resolved. The first is the presence of a white, irregular microscopic deposit just deep to the anterior surface of the lens, and the second is the presence of whorl atrophy in the iris. The pattern of the iris becomes twisted as if the sphincter has been rotated slightly. Both these signs can provide useful evidence of a previous attack that has resolved spontaneously.
Measurement of the intraocular pressure at this point could reveal a reading of 70 mmHg or more. Gentle palpation of the globe is usually enough to confirm that the eye has the consistency of a brick, especially when the pressures of the two eyes are compared. It should be realised that digital palpation of the globe can be misleading and the method cannot be used to detect smaller rises in intraocular pressure with any degree of reliability (Table 12.2).
Examination of the other eye will reveal a shallow anterior chamber. Shining a focused
Table 12.2. Signs of acute glaucoma.
• Corneal oedema with resulting poor visual acuity
• Shallow anterior chamber
• Ciliary injection
• Semidilated oval pupil (caused by iris ischaemia)
• Tenderness of globe
• Hard eye beam of light obliquely through the cornea and noting the width of the gap between where the light strikes the cornea and where it strikes the iris can assess the depth of the anterior chamber. After inspecting a few normal eyes in this way, the observer can soon learn when an anterior chamber is abnormally shallow. This facility is important to anyone who intends to instill mydriatic drops into an eye. A shallow anterior chamber does not contraindicate mydriatic drops but it does indicate the need for extreme caution and care that the pupil is afterwards restored to its normal size. The angle of the anterior chamber itself is not exposed to direct inspection and it can only be seen through a gonioscope (Figure 12.7). This instrument is a contact lens with a mirror mounted on it and through it, the width of the angle can be estimated. If the angle is open, the various structures adjacent to the iris root and inner surface of the peripheral cornea can be identified. Gonioscopy forms a routine part of the examination of any patient with glaucoma, although in acute narrow-angle glaucoma the presence of a closed angle can often be presumed by the presence of the other physical signs. Where there is any doubt, it might be necessary to apply a drop of hypertonic glycerol to the cornea to clear the oedema before applying the gonioscope.
The sooner closed-angle glaucoma is diagnosed and treated, the better are the results of treatment. Unfortunately, it is in the early sub-acute stage of the disease that the diagnosis can be difficult. A number of provocative tests have been devised for the patient who presents with suspicious symptoms but a normal intraocular pressure. The simplest test is the "dark room test". The patient's intraocular pressure is meas-
ured before he or she is seated in a darkened room for half an hour. The intraocular pressure is again measured immediately after this, and a rise in pressure of more than 5 mmHg can be taken to be significant. Certain drugs can have a similar effect by having a mildly mydriatic action when taken by mouth. The pheno-thiazines have been incriminated in this respect. Of course,such drugs will have no adverse effect on patients who have already been treated and identified as cases of narrow- or closed-angle glaucoma. Only in unsuspected cases of subacute narrow-angle glaucoma is there a real risk of precipitating an acute attack.
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