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 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 »
The first step in the operation itself is the securing of the eyelids. This is usually done with a small spring speculum, which gently holds the lids open without in any way pressing on the eye.
The removal of the cataract can be achieved in a number of ways, the aim being to clear all the opacity from the pupil of the eye. Basically, there are two methods either of which may be used: 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 »
There is a popular misconception that cataract surgery cannot be undertaken until the cataract has reached a particular ripeness. This was the case many years ago, when the only method of removing the cataract was by the extracapsular method, which involved opening the capsular bag and washing away its contents. If the cataract was very ‘immature’, it was technically rather difficult to do this. 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 »
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 »
The problems of cataract glasses result from the fact that a thick lens has to be worn in front of the eye. The nearer to the eye the lens is worn, the less will be the magnification. Nearly all the problems of cataract glasses can be eliminated if a contact lens is worn.
Because the contact lens is worn on the cornea itself, the problems of magnification almost disappear, although not entirely. 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 »
