The spectacle lens that corrects short sight or myopia is a negative power: light rays from distant objects are bent in such a way that they become more, not less, divergent. The degree of divergence will depend on the power of the lens. When the degree of (artificial) divergence is equal to the degree of short sight, the eye will form a clear image on the retina. A usual degree of short sight is up to —8.00 dioptres. But in fact it is how healthy the back of the eye remains, and how thin the outer coats of the eye become, that determine the future of the shortsighted person. Read the rest of this entry »
Secondly, such rays (peripheral vision) may be scattered by such scarring and cause unusual sensitivity to bright light. The cuts may also damage the very sensitive deeper layers of the cornea creating problems in later life, although the operation is too new to know whether and to what extent this is the case. The effects of cuts cannot easily be measured, while the ability of the tissue to heal totally may prejudice even the short-term benefits. The presence of a small degree of short sight may seem a great inconvenience to a young person, and he or she is often willing to take a long-term risk for the sake of an immediate improvement. Read the rest of this entry »
It is known that because of inheritance not everyone will have eyes of the same size and optical power, that some eyes will fail to achieve ‘normal’ functional standards. Thus at least 15 per cent of us will have developed some degree of short-sightedness by the age of twenty-five, owing to the eye not growing in balance with the rest of the optical system seen as a whole. But this statistic applies only to post-industrial populations. The incidence of short-sightedness is much less among preindustrial peoples, and so it cannot be hereditary factors alone that are at work. The correlation is between short-sightedness and socio-industrial development, not necessarily between short-sightedness and race. There are as many short-sighted Japanese as there are short-sighted Europeans. It could be argued that where pre-industrial conditions still exist the mechanics of natural selection have ‘weeded out’ congenital short sight, but it seems much more likely that a tendency-towardsshort-sight-given-certain-conditions is inherited, and inheritable, among all peoples. Read the rest of this entry »
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 »
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 »
Adults who become blind after several decades of normal or at least useful sight represent a different problem. Their psychological and practical difficulties are manifold. The sudden onset of blindness is a terrifying experience. Apart from the helplessness and inability to become mobile there is a horror of incapacity, accompanied by the realization that without help the sufferer is completely isolated, socially and physically. The adult who becomes blind is liable to become deeply embittered, much more so than if he or she had lost a limb. The loss of a limb is measurable and understandable. Sudden blindness is far more abstract, for a while incomprehensible. And because the loss of sight is rarely complete, the patient lives in hope of cure. Bouts of depression alternate with pitiable optimism. If the patient is rich, or if the public health authority permits, he or she will seek charlatan as well as professional advice. He or she will become subject to advice from the market place, faith healers and the like. Newly blind people will sometimes travel grêat distances to seek remission. If religious they will seek shrines and miracles (and some people become religious when they become blind). Equally they will alter their philosophy of life, to purge that which is supposed to have robbed them of their sight. Read the rest of this entry »
There is a well-known story about Noel Coward. The dramatist was out walking with two small children one day when the party came into view of two dogs engaged in the act of copulation. `Uncle Noel, what are they doing?’ cried one of the boys. ‘It’s perfectly obvious,’ replied Coward. ‘Can’t you see? The dog in front is blind, and the dog behind is pushing him to St Dunstan’s!’
The subtlety of this anecdote lies in the substitution of one taboo subject by another. Historically, blindness has carried different cultural connotations. Among the ancients it was often considered as a punishment meted out by the gods. In the best known of the Greek myths, Oedipus gouges out his own eyes in a hubristic act of self-inflicted retribution. In modern times blindness is more simply perceived as a misfortune. Read the rest of this entry »
This not always possible for people to go to a competent I physician for relief. As the method of treating eye defects presented is comparatively new, it may be impossible to find a physician in the neighborhood who understands it, and a person may not be able to afford the expense of a long journey or take the time for treatment away from home. To such persons I wish to say that it is possible for a large number of people to correct defective eyesight without the aid either of a physician or of anyone else. Read the rest of this entry »
It is also obvious that the method must have prevented other errors of refraction, a problem which previously had not even been seriously considered, because hypermetropia is supposed to be congenital and until not long ago astigmatism was also supposed to be congenital in the great majority of cases. Anyone who knows how to use a retinoscope, however, can demonstrate in a few minutes that both of these conditions are acquired; for no matter how astigmatic or hypermetropic an eye may be, its vision always becomes normal when it looks at a blank surface without trying to see. Read the rest of this entry »
