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 »
As we get older, all our blood vessels acquire harder walls, making it more difficult for the heart to pump blood through the whole system, especially the smaller vessels. Resistance to the flow of blood results in increased, or ‘higher’, blood pressure. The heart simply has to work harder in order to meet and overcome the developing resistance. The small vessels of the retina, or arterioles, can be examined minutely with an ophthalmoscope and changes of hardness in their walls easily seen. Because they are so small and fine they are sometimes the first to break down, so that if the blood pressure becomes very high they may leak blood and serum. When this happens the results can easily be seen on the surface of the retina between the vessels. 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 »
