Severe deafness cripples a patient's mind by preventing him communicating with other people. It is thus a serious handicap, and, alas, a neglected one. About 5 million people in the world are profoundly deaf and a further 200 million partly so; as usual, most of them are in the developing world. Try to find out the incidence of deafness in your district, and the common causes for it. The most common one will probably be chronic suppurative otitis media of the tubotympanic, mucosal, or ''safe' type.

Deafness can be: (1) Conductive, due to disease in the external canal and middle ear cavity, up to the oval window. (2) Sensorineural, due to disease of the cochlea, eighth nerve or brain.

Much conductive deafness in the rural tropics is the result of chronic suppurative otitis media, which persists because of a patient's poor general health and nutrition. His middle ear becomes acutely infected, and his drum perforates. He fails to get the prompt, short (2 day), high doses of antibiotic (preferably ampicillin) that would cure him. Instead, his acute otitis media fails to resolve, his drum does not heal, his ear continues to discharge, and its ossicles are damaged. This is less likely to happen with the common tubotympanic ''safe' type of chronic otitis media, than it is with less common attic, bony, or ''unsafe' type (25.3). Unfortunately, chronic middle ear disease is not suited to the ''eye camp' approach, which is so successful in treating blindness due to cataracts.

Sensorineural deafness is usually high-tone and incurable, but a properly fitted hearing aid helps. You are unlikely to have an audiometer, so make good use of a tuning fork.

Prevent deafness by making sure that: (1) Middle ear disease is diagnosed and treated in primary care. (2) Anyone working in a very noisy environment wears ear plugs, or muffs. (3) In areas where genetic, early, progressive sensorineural deafness is common, as it is in parts of India, do what you can to discourage cousins from marrying one another.

Very many deaf people, of any age from infancy onwards, can be helped by a modern hearing aid, which usually helps conductive deafness, if there is not too much high frequency loss and no discharge. Unfortunately, hearing aids are expensive, and need to be fitted carefully; heat and moisture rapidly inactivate them, and batteries are difficult to get. One health worker advertised for second-hand ones in Europe, and received a hundred, mostly working. This source, and methods of finding, selecting, and importing the most suitable second-hand ones for particular patients, needs following up.

A useful source of information, and of hearing aids, is: The Commonwealth Society for the Deaf, 105 Gower Street, London WE1E 6AH.

DEAFNESS EXAMINATION (adults) Always do the next two tests as a pair; separately they will not give you the information you need. Unlike an audiometer, a tuning fork is robust.

RINNE'S TEST. Strike a tuning fork (512 Hz) gently against your knee or elbow (not against a hard surface, or unwanted overtones will be produced). Place the foot of the vibrating fork firmly on the patient's head, just above and behind the ear to be tested; press with sufficient pressure to need your other hand to support the other side of his head. Then place the fork, still vibrating, with the flat side of its tines towards his ear canal. Ask him ''Which sound is loudest?'' If air conduction is better than bone conduction, sound is being conducted normally to his cochlea, but he may still have a sensorineural loss. If bone conduction is better than air conduction, he has a problem with sound conduction (middle ear disease).

CAUTION ! Beware of the false negative Rinne test. If he has severe sensorineural deafness in one ear, bone conduction may be better than air conduction (wrongly indicating conduction deafness or middle ear disease), because the sound is conducted through his head, so that he hears it in his other ear. Weber's test will distinguish this.

WEBER'S TEST. Strike the tuning fork against your knee, place its foot on the top of his head, and ask him to say which ear hears the sound loudest. If he has conductive deafness in one ear (a negative Rinne's test, bone conduction heard better than air conduction), he will hear the tuning fork better in that ear. If he has sensorineural deafness, the sound will be loudest in his better functioning cochlea.

EXAMINATION (children) In a child under 3 years neither a tuning fork nor an audiometer are useful. Unless you have special equipment you have to use: (1) His parents' account of an abnormal behaviour response, or his failure to make proper speech sounds. Or, (2) the distraction test, which is effective in most young children.

THE DISTRACTION TEST is a valid screening method. Find a sensitive and understanding assistant, and practise making the test noises, which are the syllables of the word ''shoe'', spoken separately as two tests, a high-pitched ''Shsh[...]'' and a low, sung ''Ooo[...]''. Make them softly, just loud enough for your assistant to hear.

Sit the child on his mother's knee facing your assistant. Meanwhile, remain out of sight behind his mother. Ask your assistant to gain the child's attention a little, by moving a toy up and down in a vertical line, while making the test sound. Then, ask him to hide the toy and break eye contact. At this exact moment, make a ''Sh[...]'' sound about 60 cm from the child's ear, and level with it, while you remain out of his sight. A normal child immediately turns towards the source of the sound. Reward him with some encouragement. Now test his other ear with an ''Ooo'' sound, before returning to the first ear with an ''Ooo'' sound, and then the second ear with a ''Sh[...]'' sound. To avoid false results, be sure to test his ears alternately.

If there is no response, try louder sounds. Then try a visual or tactile stimulus. If he still does not respond, suspect mental retardation, or some non-audiological problem. If he does respond, repeat the sound stimuli at 2 or 3 metres, first in a louder voice,, and then in a normal one.

CAUTION ! (1) This is a very reliable test[md]if you do it carefully. Otherwise, you can easily get false positives, and false negatives. (2) Before the test itself, practise both the manner of attracting the child's attention, and the sound to be made. (3) Timing is critical. (4) Make sure his mother does not give him any clues, consciously or unconsciously. (5) You will get a false positive if you show yourself, or let him see the test object either directly, or reflected in a window, or some reflective object, or give him some tactile clue. You will get a false negative if he is bored, tired, or distracted by other things. If this happens, don't persist; try again later.

THE MANAGEMENT [s7]OF DEAFNESS The above tests should tell you where the lesion is. Here is a guide as to what it is.

IN THE EXTERNAL EAR conductive deafness can be caused by wax, and foreign bodies (25.5), or external otitis. Rarely, a tumour is responsible, or a child is born with a closed external canal.

IN THE MIDDLE EAR conductive deafness is caused by fluid in the middle ear (often associated with a cold), and acute or chronic otitis media. Otitis media is indicated by a discharging ear.

If he has conductive loss and his drum is normal, suspect otosclerosis, especially if he has a family history. This is not found in pure West Africans (or Japanese), and is rare in other Africans, but is not uncommon in Indians. A hearing aid is safer than stapedectomy by anyone but a real expert. ''Dead ears' are not uncommon, even after the ''best' surgery.

IN THE COCHLEA AND BEYOND sensorineural deafness is often congenital, but may be due to mumps, measles (not uncommon), rubella, other viruses, bacterial meningitis, and excessive noise (''boilermaker's deafness', ''disco deafness'; all Trinidad steel band players are profoundly deaf over 2 kHz). Commonly, it is due to old age (presbyacusis), sometimes Meni[gr]ere's syndrome (deafness, vertigo, and tinnitus), and very rarely to an acoustic neuroma. This probably never occurs in Africans[md]look for signs of involvement of his fifth and seventh nerves, and for imbalance due to involvement of his cerebellum.

In children, the severest acquired deafness follows meningitis. The deafness that follows mumps is usually unilateral, so it is not much of a handicap.

DIFFICULTIES [s7]WITH DEAFNESS If a BABY IS BORN DEAF, this will usually be suspected by his family. A mother who says that her baby is deaf is usually right. Don't ignore her. His intelligence will probably be normal, and an ''island' of residual hearing may remain. His parents and older siblings must make the most of this. Instruct them like this: ''Let him watch you speaking. Use speech and signs together, because you will not know which he will later find easiest. Speak slowly and clearly, and indicate familiar objects as you name them. If necessary, repeat the word close to his ear. Show you are pleased, whenever he tries to use a word, however indistinctly. Include him in as much play, and as many activities, as you can. As always, success builds on success''.

CAUTION ! Children who are born deaf cannot learn to speak unless they heave special teaching, from their parents, or someone else, from as early in life as possible.