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 »
There are a group of hereditary or congenital degenerations affecting the cornea. A few of them manifest themselves at birth, but mainly they occur in childhood and adolescence. Their onset is slow, and they are sometimes difficult to diagnose without special instruments. Ophthalmologists consider them to be metabolic in origin, most probably the result of an abnormality in one of the enzymes servicing the cornea. Read the rest of this entry »
