The eye can provide a very reliable way of diagnosing cerebral malaria, researchers in Malawi have shown. By looking at the changes to the retina, doctors are able to determine whether an unconscious child is suffering from this severe form of malaria or another, unrelated illness, leading to the most appropriate treatment.
Because malaria is so common in Africa, children may have an incidental malaria infection whilst actually having another life-threatening illness. This can confuse the diagnosis in an unconscious child. Doctors hope that widespread use of eye examination could greatly reduce the number of children dying from this major childhood killer.
In research funded by the Wellcome Trust and the National Institutes of Health, a study led by Dr Nick Beare of the St Paul's Eye Unit, Liverpool, has shown that changes to the retina were the only clinical sign or laboratory test which could distinguish between patients who actually died from cerebral malaria and those with another cause of death. The results of their study are published in the latest edition of the American Journal of Tropical Medicine and Hygiene.
"Over a million people a year die from malaria, and most of these are African children," explains Dr Beare. "Death is usually caused by cerebral malaria, a severe complication of malaria in which the Plasmodium falciparum malaria parasite causes infection of the capillaries that flow through the tissues of the brain, affecting the brain and central nervous system. This can lead to convulsions, coma and death."
Cerebral malaria is accompanied by changes in the retina, the light-sensitive tissue at the back of the eye. These changes, known as malarial retinopathy, include white, opaque patches, whitening of the infected blood vessels, bleeding into the retina and swelling of the optic nerve, the nerve that transmits visual signals to the brain. The first two of these signs are unique to severe malaria, and not seen in any other disease.
Malaria parasites live in red blood cells and make them stick to the inside of small blood vessels, particularly in the brain and also the eye. It is thought that this causes the unique whitening of eye blood vessels. The light-sensitive tissue in the eye is also affected because the parasites disrupt the supply of oxygen and nutrients. However, once children recover, their vision does not seem to be affected.
"In cerebral malaria, the eye acts as a window onto the brain, providing valuable information for the doctors caring for the patients," says Dr Beare. "Our research demonstrates that the detection of malarial retinopathy is a much needed diagnostic tool in cerebral malaria, and can identify those children at most risk of death. Diagnosis requires special training in eye examination, but is relatively straightforward and cost effective, which is essential in resource-poor settings such as Africa."
Doctors are able to carry out this diagnosis using just an ophthalmoscope, an instrument through which the observer can see the retina at the back of the eye.
Researchers in Malawi have previously shown that up to a quarter of children apparently dying from cerebral malaria in fact had another cause of death. Dr Beare and his team hope that by confirming the diagnosis of cerebral malaria, appropriate care can be targeted at those most in need. By identifying children who might not have cerebral malaria other causes of coma can be searched for, and potentially treated.
Commenting on the research, Dr Sohaila Rastan, Director of Science Funding at the Wellcome Trust, said: "This work is impressive and if it can be effectively delivered in a resource-poor setting could have a significant impact on the diagnosis and subsequent treatment of cerebral malaria in children."