The colour of your eyes is inherited. The colour and pattern of the iris are as individuated as fingerprints. It is coated on its back with brown-black pigment. This prevents light penetrating to the back of the eye except through its centre, or pupil. This hole can change its size, dilating or contracting as the level of light requires. In bright light, or when we wish to scrutinize a near object, it contracts. In dull light, or when we wish to relax our eyes and stare in the distance, it dilates. It also becomes bigger if we are frightened or excited, and it dilates in death. Read the rest of this entry »
It would seem appropriate, therefore, to regard the whole visual system at birth as a more or less ready-to-use computer that has not yet been programmed. The actual programming takes place soon after birth; but just when this happens is not the same with all living beings. Once the programme has been supplied it remains built-in for life; but to function well it requires frequent use, especially in the early years. Read the rest of this entry »
When light rays from a distant object pass through the cornea only the central rays are likely to form an image on the central and most sensitive part of the retina. Only the central part of the cornea (an inner diameter of between 3 and 5 mm) is sufficiently curved to bend the light-rays regularly. The light entering the more peripheral parts of the cornea only stimulate the more peripheral parts of the retina. These are bent irregularly and do not form a clear central retinal image. This ‘peripheral vision‘ is most useful for locating objects in space, and, by a reflex nerve stimulation, regulating the size of the pupil. Read the rest of this entry »
The immediate appeal of contact lenses is social. The desire of spectacle wearers to be ‘normal’, to appear in public without a facial contraption, is very real. In the USA, Europe and Japan most young short-sighted people have, by the age of twenty-five, at least tried contact lenses if their vision requires the daily or continual use of spectacles. Some patients will even persist through considerable discomfort in order to achieve ‘normalization’. And as more and more people adopt contact lenses, it becomes less and less normal to wear glasses. It is as well therefore that, apart from its cosmetic advantages, the contact lens also has some optical advantages. Read the rest of this entry »
At one time almost all intraocular surgery was performed under a local anaesthetic. For two reasons local anaesthesia is used much less commonly today. First, the whole science of general anaesthesia has greatly advanced and the likelihood of coughing has been considerably reduced. Second, methods of repairing the cataract wound are now better than they used to be. Coughing and sneezing after the operation consequently constitute less of a threat than formerly. Read the rest of this entry »
These then are the common errors of vision which may cause eye-strain. They are short- and long-sightedness, near-vision deficiency and astigmatism. Most commonly astigmatism is present with one of the other three conditions. They may all be measured by both objective and subjective methods. Objective measurement means the use of instruments, while subjective measurement requires you to state an opinion. In ordinary practice the practitioner will use both methods, and thereby establish a pattern which enables him to prescribe the right optical correction. If you repeatedly give a wrong answer to a subjective inquiry the experienced occulist will proceed to further objective (optometrical) tests. Read the rest of this entry »
Squint, or strabismus, is a general term used to describe any one of several conditions in which the two eyes are not properly co-ordinated. One eye focuses on an object, but the other eye fails to align itself to the same fixation. Most commonly the errant eye is aligned inwards (cross-eye or esotropia) or outwards (wall-eye or exotropia); less commonly it looks upwards (hypertropia) or downwards (hypotropia). Other words to describe these conditions are ‘cast’ and ‘turn’. The phrase ‘evil eye‘ has also doubtless been used in association with squint. Where a squint remains uncorrected the person who has it is often forced to adopt an unusual, even grotesque, head- posture, adding to a general impression of unsightliness. But because the squint sufferer has the potential for normal stereoscopic vision the treatment of squint is an important ophthalmic activity. Read the rest of this entry »
Where cataract is due to abnormal body metabolism, then treatment of the metabolic disorder can sometimes prevent development of cataract, or even reverse cataract where cataract has begun. Diabetes mellitus is a good example of this. Otherwise metabolic cataract can be treated by conventional methods. It should be said at once that in most countries of the world eye-drops and medicines of ill-founded clinical value, and rarely backed by any sound medical trials, are still available. Read the rest of this entry »
The retina, then, is a nerve pad dependent upon a complex network of support systems. One of these support systems is a supply of blood, for it is in the blood that many of the essential nutrients are carried from one part of the body to another. Therefore the eye, and more particularly the retina, is or can be affected by deficiencies in other organs. The retina is in fact fed by blood systems both in front and behind, and many blood diseases can have a deleterious effect on retinal functions; and both systems are sufficiently intricate and fine to be hypersensitive to abnormalities in the blood. However, since the variations and permutations of retinal degeneracy are enormous it is sometimes very difficult to diagnose its cause. It is always possible to describe what one sees as being wrong with a decayed retina, but even after many specialized tests it can still be impossible to say with any accuracy what is the precise cause. This has seriously hampered the treatment of some retinal conditions. Where the cause of a disease is known it is always much easier to prescribe a cure, or at least medication that will halt or slow down what is usually a progressive condition. Read the rest of this entry »
A very common phenomenon of imperfect eye sight is that one, already mentioned, which is known as muscae volitantes, or flying flies. These eye floating specks are usually dark or black, but sometimes appear as white bubbles, and in rare cases may assume all the colors of the rainbow. They move somewhat rapidly, usually in curving lines, before the eyes, and always appear to be just beyond the point of fixation. If one tries to look at them directly, they seem to move a little farther away. Hence their name. Read the rest of this entry »
