Eye Care Blog

The retina, or rear receptor part of the eye, consists of a layer of different kinds of cell which meet the demands of different kinds of sight: detail and outline, colour, light and dark. But these cells cannot work unless they can produce the chemicals used to react with light energy, and the chemicals that are used to transmit the light-nervous energy to the brain. These chemicals and their application are a vastly complex subject which is still being explored; but it is known that all the products needed for retinal function come, in the last analysis, from the blood supply. Some of these come ready-made, some have to be synthesized at the point of use. Any deficiency in the blood stream, or any chemical deficiency in the retinal cells, may therefore create abnormal vision. In addition, the blood has its own set of specialist cells that are designed to combat infection and foreign proteins, and these cells, if over-activated, may themselves cause disorders. To some extent a process of degeneration and repair is inbuilt in our bodies, even during periods of excellent health. But if these reactions get out of hand they may cause more problems than the original disease or degeneration. The whole subject is called immunology, and includes hypersensitive reactions such as allergy. With so many new chemicals in daily use, and so many new medications, it is a peculiarly modern symptomatology.

The blood coat that lies between the retina and the sclera (outer tunic) is known as the choroids. The retina is in contact with its smallest branches (capillaries), and the retinal cells are separated from the capillaries by membranes and a potential space, which can become a real space filled with fluid either from the choroid or from the vitreous. As has already been explained, the usual cause of retinal detachment from the choroidal membrane is due to fluids from the vitreous flowing through tears in the retina. But the choroid itself can separate from the sclera (choroidal detachment), in which case fluid can enter the potential spaces of the retina from the very back of the eye. This indeed sometimes happens after either cataract or glaucoma-filtering operations, but does not necessarily lead to very great visual impairment.

But the retina is not the only tissue to be supplied with nutrients by the choroid. It also feeds the ciliary body, just in front of the equator of the eye, and the muscle it contains, with nourishment and oxygen.

Inflammation of the choroid and its feed-tissues can be seen in the form of various reactions using an ophthalmoscope or slit-lamp bio-microscope. The circulation of blood in the choroid can furthermore be studied by using fluorescein. Fluorescein is injected into the blood system, and its traces are then photographed (an `angio-fluorogram’) . A similar but more sophisticated technique for examining the back of the eye is the use of tracer elements that have irradiated molecules in them, the response being measured on radio-active receptors which produce an exact mathematical quantification.

With these technological aids we can see and record abnormalities in the choroidal blood system. Some of these abnormalities, or diseases, are blood-borne. That is to say, the disease of the eye may turn out to be a symptom of a disease of the blood, and this could be microbiological or macrobiological. More simply, the blood may contain the wrong nutrients, or certain metabolic hormones may be absent. Or there may be a circulatory problem connected with heart disease. Every tissue of the eye depends upon the blood it gets from the choroid, and therefore any irregularity in that supply is likely to show up as a degeneration in one part of the eye or other. Another possibility is the presence of cancer cells in the blood, carried to the eye, or part of a generalized cancer change in the body. And so on. Indeed, disease in any part of the body can affect the eye, and so the list is inexhaustible. It is for this reason that ophthalmologists are required to have a sound general medical background.

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