Glaucoma

Glaucoma is a group of blinding diseases in which a patient's intraocular pressure (IOP) is usually raised, causing damage to his optic nerve, and resulting in loss of vision. There are four kinds: (1) Primary (chronic) open-angle glaucoma (POAG). (2) Primary angle closure glaucoma (ACG). (3) Secondary glaucoma as a complication of trauma, swollen cataract, iritis, etc. (4) Congenital glaucoma (buphthalmos).

POAG occurs in eyes in which the angle between the iris and the cornea is normal, and is probably due to a block in the drainage of intraocular fluid at the trabeculum. POAG causes 10[nd]20% of blindness in developing world, 90% of glaucoma in Caucasians, and most cases of glaucomatous blindness in Africans. Up to 1% of the over-40s may have it. POAG is bilateral, but is often asymmetrical; it is insidious and progressive, and causes no symptoms until a patient has lost much of his sight. Glaucoma cannot be prevented, and even early treatment cannot restore lost vision. The best that can be done is to recognize it early, and to prevent his vision getting worse. For this to be possible, all health workers must be aware of the possibility of glaucoma in any patient who complains of loss of vision. The key to early diagnosis is to pick up early changes in the optic discs and a raised IOP, both of which can be recognized by eye assistants. The aim of medical and surgical treatment is to lower the IOP to a level which will stop further damage to his optic nerve, and therefore preserve his vision at its present level. Trabeculectomy (not described here) is a relatively simple operation, with a reasonable chance of preserving what vision he still has. It should be available at a referral hospital, or at another district hospital, where there is a surgeon interested in doing it. Learn it from an expert at the same time that you learn cataract extraction.

The symptoms of POAG are non-specific. The patient complains of slow loss of vision in one or both his eyes over months or years (''loss of vision in a white eye', 24.4). Sometimes, he has marked loss of vision in one eye, while his other eye is normal, or nearly so. Occasionally, he has pain and headache, but this is late. Glaucoma is often familial, so inquire about blindness in his relatives.

Angle closure glaucoma (ACG, acute glaucoma) usually occurs over the age of 35, in women more often than men, with an abnormally narrow angle between the iris and the cornea. If this angle should happen to close a little more than usual, it causes a sudden abrupt rise in a patient's IOP, so that he presents with unilateral episodic attacks of pain, misty vision, and rainbow-coloured haloes round lights. Between attacks his eye is normal. Sooner or later, an episode of raised IOP does not resolve, and he presents with classical acute congestive glaucoma (''loss of vision with a red eye', 24.3). Acute glaucoma is relatively uncommon, and is rare in Africa. Its incidence is highest in Inuits and Mongolian peoples, in Burma, and in South East Asia.

The dangers of atropine in glaucoma result from its effect in dilating the pupil: (1) This keeps the iris away from the lens, and prevents adhesions (synechiae) forming between them, which is valuable in iritis when you want to prevent this happening. (2) Dilatation of the pupil crowds the iris into the angle of the anterior chamber, where it impedes the drainage of aqueous. This is never a desirable effect, but it does not matter in a normal eye or in iritis; it can however blind an eye if drainage is already impaired by glaucoma! So, do give atropine in iritis, but don't give it in glaucoma!

IF AN OLDER PERSON COMPLAINS OF POOR VISION, CHECK FOR GLAUCOMA. Fig. 24-8 SOME LEFT OPTIC DISCS. A, a normal optic disc with a moderately sized cup and the lamina cribrosa shown stippled. B, another normal optic disc. This has a large physiological cup and a temporal scleral crescent. C, the optic disc of a patient with gross ''chronic' open-angle glaucomatous cupping. After Parr, Jon, ''Introduction to Ophthalmology', (2nd edn 1982). OUP, with kind permission.

GLAUCOMA PRIMARY OPEN-ANGLE GLAUCOMA, [s7]''POAG', ''chronic glaucoma' DIAGNOSIS. Measure the visual acuity of any patient who presents with loss of vision. A hazy cornea or a pupil which does not respond normally to light should make you suspect glaucoma. If his IOP is [mt]28, or his cup/disc ratio is [mt]0.5, he may have glaucoma. The end stage of glaucoma is a patient with a blind, or nearly blind eye, with a large pupil that does not react to light. Aim to diagnose it long before this with the following three tests. Loss of visual field is an early sign, but is not easy to test for with simple equipment.

CAUTION ! (1) The IOP is useful in confirming glaucoma, but is not absolute. (2) Glaucoma can occur with a normal IOP (30% of patients with glaucoma have an IOP of [lt]22 mmHg). (3) A raised IOP is not always associated with optic nerve loss. (4) The IOP fluctuates, so if you are in doubt, repeat the measurements over a few days.

(1) LOSS OF VISUAL ACUITY is not an early sign in POAG, but it is a quick one. Always measure a patient's visual acuity, whenever he presents with an eye complaint (24.1).

(2) CUPPING OF THE OPTIC DISCS is the important sign. Chonic glaucoma causes the discs to become deeper and wider, and the remaining rims of disc tissue to atrophy. One eye is commonly affected more than the other, so that a definite difference between a patient's two eyes is probably abnormal. Enlargement starts at the upper or lower margins, so that a vertically ovoid cup with a cup/disc ratio of [mt]0.5 is probably abnormal. Eventually, the margin of the cup approaches the margin of the disc, so that only a narrow rim of tissue remains. Its wall becomes steep, so that vessels bend abruptly as they reach the level of the surrounding disc. If the edge of the disc overhangs the cup, you may lose sight of them until they appear over the edge of the cup. A large physiological cup can be difficult to distinguish from an early glaucomatous one.

With practice, eye assistants can distinguish ''normal discs', ''suspicious discs' and ''advanced glaucomatous cupping'. If you can only do one test, changes in the discs are the most useful one. If necessary dilate his pupils.

Normal discs: (1) The discs are the same in both eyes. (2) The ratio of the optic cup to the optic disc is 0.5 or less. (3) The cup is circular and the periphery of the disc (the optic nerve rim) is pink. (4) The appearance of the disc remains constant over time.

Signs suggestive of glaucoma: (1) A cup/disc ratio of greater than 0.5. (2) A vertically oval cup, perhaps with notching at the upper or lower poles. (3) An area of pallor [mt]30% of the disc area. (4) Asymmetry of the cup/disc ratio between the two eyes.

Fig. 24-9 GLAUCOMA. A, a normal visual field with its normal blind spot. B, a paracentral scotoma (blind area) in early glaucoma. C, an arcuate scotoma in early glaucoma. D, a ring scotoma in early glaucoma. E, complete loss of visual field apart from a small central island, and a larger temporal island, in advanced glaucoma. Unfortunately, there is no easy way of monitoring the visual field in glaucoma.

F, a schematic representation of the cup/disc ratio. G, a normal optic disc with its physiological cup. H, a cup/disc ratio of 0.5, the borderline of normality. I, pathological cupping of the optic disc due to glaucoma with a cup/disc ratio of 0.7. Kindly contributed by Allen Foster.

(3) ABNORMAL PUPIL RESPONSES are a useful way of testing for glaucoma, and only need a torch. Initially, one pupil does not react as briskly as the other. Finally, there is no response at all.

If you shine a light into a normal eye in a semidark room, its pupil will constrict (direct response), and so will the other pupil (consensual response).

If his optic nerve is completely destroyed, there will be no direct or consensual response (total afferent pupil defect).

If his optic nerve is partly destroyed (for example 90%), his pupil will constrict slowly when the light shines in it (partial afferent pupil defect), showing that only a little optic nerve is functioning.

The swinging torch test, is a useful test for early asymmetrical optic nerve damage, and does not need an ophthalmoscope. It is theoretically difficult, but is easy in practice. In a semidark room shine a light into his good eye, and then swing it across into his bad eye (the eye with reduced vision).

As the light shines in his good eye, the pupil of his bad eye will constrict. As you swing the light quickly across to his bad eye, its pupil, which was previously constricted, will now dilate. This indicates a relative afferent pupil defect, early optic nerve damage, and a difference in function between his two optic nerves.

The practical test is to swing the torch from one pupil to the other and back again in a semidark room. If one pupil consistently dilates as light shines on it, that eye has a reduced pupil response, relative to the better eye, and should be investigated for optic nerve disease, perhaps POAG.

THE RISK FACTORS FOR POAG are: (1) Age [mt]40. (2) A positive family history in first-degree relatives. (3) Race, POAG is more common in Africans than in Caucasians. (4) A vertical cup/disc ratio of [mt]0.5. (5) An IOP of [mt]28 mmHg ([lt]2 with a 5.5 g weight).

MANAGEMENT will preserve what sight he has, but will not improve it.

If he is already blind in both eyes and unable to walk about by himself, it is too late to help him.

If he has any sight left (he can walk about by himself with either eye), refer him immediately for trabeculectomy. Even when his sight is as poor as CF 1 m (24.1), he may still derive some benefit from treatment. If you cannot refer him, or do a trabeculectomy yourself, you will have to try medical treatment:

Medical treatment can lower his IOP, but it has to be constant, consistent and continue for life, which is usually impracticable, so that immediate surgery is better. The drugs are: (1) Pilocarpine 4% 4 times daily. (2) Timolol 0.5% twice daily (expensive). This is a [gb]-blocker which reduces the secretion of aqueous. (3) Acetazolamide tablets 250 mg 4 times a day. Start him on pilocarpine or timolol, and if this fails to maintain his IOP [lt]20 mmHg, also give the other drug. If both drops fail to lower his IOP below 20 mmHg, give acetazolamide 250 mg 1 to 3 times daily for short periods (side- effects may occur with continued use). To treat him effectively, you will have to measure his intraocular pressure, and monitor his visual fields regularly. This has to be done in a specialist clinic.

Surgical treatment is a trabeculectomy which removes a piece of the filter (the trabecular meshwork), and so allows his intraocular fluid to drain under his conjunctiva; this increases drainage and reduces his IOP. The operation has an immediate success rate of [mt]80%, and is the recommended treatment for most patients with POAG in the developing world.

''ACUTE GLAUCOMA' This is is usually due to ''ACG' (angle closure glaucoma), but secondary glaucoma (see below) may occasionally present acutely.

DIAGNOSIS. He presents with an ''acute red eye' at any age (one of its rarer causes, 24.3), severe unilateral headache in and around his eye, and sudden profound loss of vision. When you examine him, his vision is reduced, his eye is red, his cornea is hazy from oedema, his anterior chamber is shallow, his pupil is usually dilated, and his intraocular pressure is usually over 40 mmHg.

CAUTION ! He will go blind unless you treat him quickly.

TREATMENT. Admit him as an emergency. Refer him to an ophthalmologist as soon as possible, who will decide whether to do a trabeculectomy or peripheral iridectomy, or whether to treat him medically. If referral is delayed, start treatment before he goes. If you cannot refer him, you will have to treat him medically yourself. Give him an analgesic to ease his pain, and treat both his eyes. Aim to:

(1) Lower his IOP by increasing the drainage of aqueous. Give him acetazolamide 500 mg orally followed by 250 mg 6-hourly, as soon as his nausea has subsided.

(2) Keep his pupils constricted. This will keep the periphery of his iris away from the angle of his eye, where the aqueous flows out, and so help it to drain. Treat both his eyes with drops of pilocarpine 1[nd]4% every 15 minutes, for 2 hours. If this makes his pupil constrict, the angle will be opened.

(3) If necessary, you can also lower his IOP by increasing the tonicity of his blood. Give him 50 ml of flavoured glycerine by mouth. If he is nauseated, he may not tolerate this. Or, give him 200 ml of 20% mannitol intravenously during 20 minutes.

When medical treatment has reduced his IOP to normal, he needs a peripheral iridectomy soon, to prevent a future attack, and probably a prophylactic one on the other side also.

CAUTION ! (1) He can become totally blind in 12 hours, so treatment is urgent. (2) Rainbow-coloured haloes round lights, and misty vision, are important prodromal signs, and need urgent investigation and treatment. (3) Atropine can precipitate an attack in a patient with a shallow angle, so avoid it in such people.

SECONDARY GLAUCOMA This complicates: (1) Trauma, including hyphaema (blood in the anterior chamber, 60.8). (2) Swollen cataract (see below). (3) Some cases of iritis. Treat the primary condition, and refer him. If you cannot refer him, treat him with acetazolamide, mannitol, or glycerol as above.

DIFFICULTIES [s7]WITH GLAUCOMA If he has an acute RED PAINFUL EYE, a shallow anterior chamber with a hazy cornea, and a FIXED, DILATED WHITE PUPIL, he has a SWOLLEN CATARACT, causing secondary glaucoma. Give him acetazolamide 500 mg immediately followed by 250 mg 4 times daily, and refer him for removal of his cataract.

If he has LOSS OF VISION and has been using steroid drops for several months, suspect STEROID GLAUCOMA. Topical steroids cause a genetically determined rise in IOP in a third of people. This is sometimes severe enough to cause glaucoma, exactly like POAG. Stop steroids.

If a child has BIG EYES, which may be associated with photophobia, blepharospasm, and tearing (''[...]such beautiful big eyes''), suspect CONGENITAL GLAUCOMA (buphthalmos, ox-eye, rare), due to maldevelopment of the angle of his anterior chamber. The sclera of a child are soft, so that his eyes enlarge when his IOP rises. Other signs are: an increased IOP, a corneal haze (variable), sluggish reaction of his pupils to light, and enlargement of his cornea ([mt]12 mm), or of his whole globe. If necessary, treat him medically and refer him immediately.