Untreatable Causes of Failing Vision

Ophthalmologists are sometimes asked if the sight can be restored to a blind eye and, as a general rule, one can say that if there is no perception of light in the eye, it is unlikely that the sight can be improved, irrespective of the cause. There are several ophthalmological conditions for which there is no known effective treatment and it is sometimes important that the patient is made aware of this at an early stage in order to avoid unnecessary anxiety, and perhaps unnecessary visits to the doctor. Most degenerative diseases of the retina fail to respond to treatment. If the retina is out of place, it can be replaced, but old retinae cannot be replaced with new. So far, there has been no firm evidence that any drug can alter the course of inherited retinal degenerations, such as retinitis pigmentosa, although useful information is beginning to appear about the biochemistry and genetics of these conditions. Age-related macular degeneration tends to run a progressive course in spite of any attempts at treatment, and although most patients do not become completely blind, it accounts for loss of reading vision in many elderly people. Some myopic patients are susceptible to degeneration of the retina in later years; known as myopic chorioretinal degeneration, it can account for visual deterioration in myopes who have otherwise undergone successful cataract or retinal surgery.

Scarring of the retina following trauma is another cause of permanent and untreatable visual loss, but the most dramatic and irrevocable loss of vision occurs following traumatic section of the optic nerve. One must be careful here before dismissing the patient as untreat-able because on rare occasions a contusion injury to the eye or orbit can result in a haemorrhage into the sheath of the optic nerve. Some degree of visual recovery can sometimes occur in these patients and it has been claimed that recovery might be helped by surgically opening the nerve sheath. There is one odd exception to this dramatic form of blindness that can follow optic nerve insult: visual loss due to optic neuritis. Patients with retrobulbar neuritis (optic neuritis) nearly always recover their vision again, whether or not they receive treatment. The explanation is that the visual loss is caused by pressure from oedema rather than to damage to the nerve fibres themselves. It is hardly necessary to say that any neurological damage proximal to the optic nerve tends to produce permanent and untreatable visual loss, as exemplified by the homonymous haemianopic field defect that can follow a cerebrovascular accident.

Malignant tumours of the eye come into this category of untreatable causes of visual failure but in fact serious attempts are now being made to treat them with radiotherapy in specialised units and the prognosis appears to be improving in some cases.

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