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 »
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 »
Contusions
Severe blows to the face and eyes are relatively rare in life; but casual blows and knocks are common, occurring mostly in the home or on the sports field. For those involved in warfare they are common enough injuries. Explosions exert great changes of air pressure upon the body, followed by a rebound as the pressure suddenly drops again. This is the invisible fist of the battlefield, and of some industrial accidents. The eye can be convulsed from its muscle connections and the orbit severely damaged. Most explosions are also associated with flying debris (it could be shrapnel, it could be glass), so that injury is often compounded by different types of damage. Other instances where contusive damage occurs are motor accidents, especially where safety belts are not worn, champagne bottle corks, squash balls and fireworks. Read the rest of this entry »
The eye has its natural protective mechanisms. The lids, for example, protect the front of the eye from dust, wind and objects coming towards the face. They also protect the eye from excessive light. The eye itself is set in its bony cavity: the orbit. In the orbit there are some soft fatty tissues which act as a cushion, permitting the eye to sustain a light blow without injury. Nevertheless the eyes are vulnerable. The eye will be injured, often severely, by fast-flying hard objects, and also by some gases and solutions. It is easy to incapacitate a human being, either temporarily or permanently, by spraying irritant solutions onto the face, and such methods have been widely used by criminals, police and the armed services. Read the rest of this entry »
