Health: Floaters and flashes

I HAVE recently developed tiny black spots in my field of vision that seem to drift about. There is no pain, but they are a nuisance. Is this the first sign of cataracts?

These are floaters, which are caused by shadows that fall on the retina at the back of the eye. Floaters are usually caused by some shrinkage of the vitreous humour, which is the jelly-like material that fills the eyeball. When the vitreous shrinks, it pulls away from the retina and this can also cause flashing lights in addition to floaters. Any sudden onset of flashing lights or floaters requires an eye examination to make sure that the retina has not torn or become detached. Simple floaters usually disappear with time. And they are not a sign of developing cataracts.

I AM 36 years old and pregnant for the first time. I was hoping to have an amniocentesis to make sure my baby is not affected by Down's Syndrome, but I have been told that I should have the "triple test" instead. Is the "triple test" as accurate as an amniocentesis?

The "triple test" is a screening blood test that is used to estimate the risk of a baby having Down's Syndrome or some other chromosomal abnormality. It measures three chemicals in the mother's blood. (Some hospitals use the "double test", which is slightly less accurate, and a few use the "quadruple test".) The results of these tests are used to make a prediction about the likelihood that she is carrying a baby with abnormal chromosomes. If the blood test shows that you have a high risk, you will probably be offered an amniocentesis. Amniocentesis, a procedure in which amniotic fluid is drawn out through a needle, is virtually 100 per cent accurate in diagnosing chromosomal abnormalities. The double, triple and quadruple tests will only pick up 50 to 75 per cent of abnormalities.

MY SIX-year-old son has recently developed scarlet fever and is now taking penicillin. What is scarlet fever, and is it contagious?

Scarlet fever is caused by an infection with a streptococcal bacteria. The illness usually consists of a throat infection, together with a widespread rash. The rash appears because the bacteria produces a toxin that circulates in the blood and causes the skin to be affected. Old medical textbooks describe scarlet fever as a serious illness with numerous possible complications, but these days it tends to be much milder. The only way to be certain of the diagnosis of scarlet fever is by taking a throat swab and detecting the streptococcal bacteria. If the bacteria is present, it can be eradicated with penicillin, though some people seem to carry the bacteria in their throats without any ill effects. The bacteria can be spread by coughing and sneezing, but not everyone who comes into contact with it will become ill.

Send your questions to A Question of Health, `The Independent', 1 Canada Square, Canary Wharf, London E14 5DL; fax 0171-293 2182; or e-mail them to: health@independent.co.uk. Dr Kavalier regrets that he is unable to respond personally to questions