State of health is all in the eyes

The eye is everyone’s window on the world, and it is the pupil - the round opening in the iris - that regulates the brightness of the images we see through that window. Now the pupil has itself become a window through which doctors can deduce our state of health, including possible addiction to drugs and susceptibility to life-threatening diseases.

The size of your pupils is determined by a range of factors, including the health of the retina and optic nerve, exposure to light, disease and even your state of mind. The pupil is controlled by two muscles, one of which causes it to constrict, and the other to dilate. In normal circumstances, these muscles, which are each controlled by different branches of the nervous system, counterbalance each other. All muscle activity is regulated by the release of neurotransmitters in the brain, which start the chain of events that results in a change in the pupils.

At the heart of the new technique is a British-made instrument called a pupillometer, the first designed for use outside a laboratory. Completely portable, it offers police or prison officers a ready way to check suspects or prisoners, giving an almost instant indication of opiate misuse.

The pupillometer, which fits into a briefcase, consists of a PC, its Pupilfit software and a camera with two lenses and special optics that give a split field of view. An infrared light source allows measurements to be made in the dark as well as in normal light.

Once the patient has looked into the device, and images of the eyes have been electronically captured, the software deploys a fast algorithm to measure the diameter of the pupils. The operator sees highly magnified images of right and left eyes displayed simultaneously, side by side, on a laptop screen. No operator intervention is needed, even if part of the pupil outline is obscured.

According to Dr. Dan Taylor, who developed the pupilometer at the Slough-based Procyon Instruments: “The advantage of pupillomentry over many other techniques is that it is both objective and noninvasive, and therefore painless. The pupil is like a little laboratory, revealing information through the automatic changes in its size when a light is flashed. This means that the patients does not need to report what they see - and so cannot lie. It makes avail-able an extremely cost-effective and fast diagnostic tool for a wide range of diseases. For instance, it is already an invaluable research tool in the diagnosis of glaucoma.”

The pupils also hold the key to ailments such as sleep disorders, cancers and eye diseases, and researchers hope to apply the new instument to spot early sings of Alzheimer’s disease. The detection of opiate addiction and other drug dependencies will, it is expected, eventually assist police and the prison service. The opiate test has been developed by Professor Hamid Ghodse at St. George’s Hospital in London. The technique exploits one of the effects of heroin in the bloodstream - a tiny constriction of the pupils, The drug acts on the central nervous system, and thus the pupils, by affecting the small number of neurons in the midbrain that control the eye muscles.

In the test, a droplit of an antagonist drug, which blocks the effect of the opiate, is put into one eye through the cornea. Once mided with the fluid of the eye, the antagonist attaches itself to the various receptors on the muscles of the iris. With the antagonist in plce, the heroin’s usual side effect of constricting the pupil is blocked, and it starts to dilate. By comparing left and right eye with the pupillometer - one eye acting as a control - the operator can then tell whether the patient has been using opiates.

In order to eliminate other possible explanations for the dilation, it is essential to observe both eyes at the same time - and this is the advantage of the pupillometer developed by Dr. Taylor, If the treated eye dilates and the other does not, opiate in the blood is the only likely explanation.

Dr. Taylor said: “The accurate and objective measurement of the pupils has enormous consequences for the correct treatment of the patient.

If opiate dependency is inaccurately assessed and an opiate is prescribed unnecessarily, this can lead to the death of patients and spillage of controlled drugs onto the black market.”

At Nottingham and Bristol Universities, his instrument is helping researchers to harness pupillomentry in distinguishing different forms of dementia, which would lead to better targetting of drugs and to track the progress of the condition. In Germany , it is being testedin the diagnosis of sleeping disorders such as daytime sleepiness, becouse pupil size can indicate whether or not the patient is excited, sleepy or feeling pain. At St Thomas’s Hospital in London, doctors are applying the new instrument to the diagnosis of diabetic autonomic neuropathy, a disease of the nervous system common amongst diabetics.

In psychiatry, the pupillomete can be used to measure psychosensory reflexes: a feeling of butterflies in the stomach, for instance, is often accompanied by dilation of the pupils. And in pharmacology, the technology provides a way of investigating the effects drugs hav on the body.

It seems that the eye is now a window into both body and soul.