In order to maintain its transparency the lens, a living structure, requires nourishment and metabolic activity. Any agency which disturbs the normal metabolism of the lens will cause a greater or lesser opacification, which is by definition a cataract. Nourishment is provided by the aqueous humour in which the lens lies, the necessary substances passing through the outer capsular membrane to reach the cells within. There are no blood vessels in the lens. Most of it consists of a form of protein, rather like egg-white, which does not occur elsewhere in the human body. Lens protein in different animals is exactly the same. This curiosity, which is called organ specificity rather than species specificity, means that if someone becomes allergic to any animal’s lens, he will also become allergic to his own. Read the rest of this entry »
Symptoms
All the symptoms of cataract are visual, the usual complaint being of a general mistiness of sight, more particularly for distance vision, as reading is often unaffected in the earlier stages. One eye is frequently worse than its fellow, but sooner or later both eyes alter. At this stage dazzle may be a cause of great distress. In normal lighting conditions vision may not be seriously disturbed, but in bright sunlight it becomes obscured by dazzle in the same way that a dirty windscreen becomes almost opaque in the headlights of oncoming cars. In this situation patients may be greatly helped by wearing a brimmed hat or tennis shade. Tinted glasses are of limited assistance because it is the direction of the light as much as its brilliance that causes the trouble. Read the rest of this entry »
When examining you an ophthalmologist will test eye-pressure through the simple expedient of placing his fingers on your closed eyelids. The experienced physician will know immediately whether the pressure is unusually high, but even so he is unlikely to be able to distinguish, using this technique, between more than four grades: namely soft, normal, suspicious and high. Accurate measurement requires instruments. Such instruments have to touch the cornea, which is therefore suitably anaesthetized beforehand, using a special kind of drop. Several types of local anaesthetic drop exist, e.g. amethocaine, pentocaine and xylocaine. One instrument blows a puff of air on to the cornea and then measures the degree of corneal flattening that results. This does not require a local anaesthetic. Read the rest of this entry »
Since the retinal nerves radiate from the cup of the optic nerve (the seat of the blind spot) the loss of retinal function tends to occur in a way that is diagnostic. For example: the group of nerve fibres that tend to be affected first are those that function in arches around the centre of vision. The next group to go are those providing vision in the nasal field (the lateral part of the retina). But it is all too possible for a patient to be unaware of these losses of vision, and because the condition is symptom-free in its early stages and only gradually progressive, diagnosis is often difficult. Read the rest of this entry »
The eye, we have seen, is a ball with a stalk behind that conveys data to the brain. The inside of the eye has been described as consisting of the light-sensitive retinal film in the back half, and a lens called the cornea and a pupil (entry hole) in the front half. The iris or coloured part has a black pigment behind it so that the whole back part of the eye globe is in darkness. Between the pupil and the retina, suspended by fine fibres or ligaments, is the inner lens of the eye, which is made of transparent layers of cells. Read the rest of this entry »
In an ideal world the best way to restore an eye to normal would be to replace the cataractous lens with a clear one of the same power lying in the position from which the original lens was removed.
At the Oxford Ophthalmological Congress the eye surgeon Harold Ridley reported the results of eight operations that he had performed to insert a Perspex lens. He thus founded a completely new branch of ophthalmic surgery. Ridley had treated many ocular injuries suffered by members of the Royal Air Force during World War II. Aircraft windshields (made of Perspex) had shattered after explosions or the impact of bullets, and Perspex fragments had penetrated the eyes of plane crews. Ridley had noticed how inert Perspex was in the eye and how little inflammation it caused. Read the rest of this entry »
As regards lens-implant surgery the benefits are very great. To be able to have normal sight again without the need for thick spectacles or the bother of wearing contact lenses is surely the preferred treatment. Where contact lenses are used subsequent to a cataract operation, they differ from ordinary contact lenses in certain ways. The condition of an eye that has had its crystalline lens removed is known as aphakia, and aphakia almost invariably demands a contact lens that is much thicker in its centre than the lens worn by the ordinary short-sighted person. Read the rest of this entry »
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. Read the rest of this entry »
