Eye Care Blog

There have been many research programmes involving humans and primates aimed at finding answers to the sort of question suggested in the preceding paragraph, but generally each attempt has only uncovered a further set of factors making any final solution, any final map of the ‘genes versus environment‘ problem, less and not more likely. Perhaps in some future era when education returns to a system that doesn’t require books, but where knowledge is computer-stored and audio- retrievable, then short-sight, where it occurs, will be more easily explicable. Meanwhile we should teach our children not to hold their heads too close to the printed page, not to read for too long periods, to use good light and to develop their distance vision in outdoor pursuits. Perhaps, too, we should encourage them to develop their thought-processes, rather than seek to fill their heads with useless data as though they were merely memory banks.

Meanwhile, as we discover how the genetic programming of our body operates, it seems more not less remarkable that the eye grows from a ball 17 mm in diameter to one 24 mm in diameter without being noticed. The cornea and crystalline lenses make the necessary changes without any disruption to `normal services’, so that the image falls consistently on the film at the back of the eye. Is there some method by which eye- growth is controlled from the nervous system in such a way that the nervous system ‘knows’ how the image is formed? In other words, if the image goes out of focus, even fractionally, does the nervous system plot the necessary realignments in all parts of the optical system so that a good picture can be swiftly restored? The alternative would be to say that the pattern of development is pre-set and will operate irrespective of any one part being out of step with the rest, that each part will grow to its required size and optical function of its own accord. While both possibilities are perfectly compatible with the diverse ways in which genetic coding operates, the second theory seems to provide a better explanation of the occurrence of visual defects, in so far as those defects are not caused by environmental factors. But as yet the genetic machinery is not fully understood; when it is, clinicians will be better able to discover ways of diagnosing early malfunctions and therefore be in a better position to suggest ways of correcting, and even preventing, them.

Counselling apart, genetic ophthalmology as a practical science belongs to the future. Abnormal developments must therefore be discussed as they occur, not as they ‘would otherwise’ occur. In general there are three areas in which optical malfunctions may take place, the three related optical components of the eye: the cornea, the crystalline lens, and the retina. Aberrations may affect any or all of these, individually or in combination. If the cornea is too steeply curved, its power will be too great and the image will fall in front of the retina, thus causing shortsightedness. This state of affairs can be theoretically corrected by reducing the length of the eye, or by moving the crystalline lens backwards, or by reducing the power of the crystalline lens in some other way (e.g. replacing it with a weaker lens). In normal circumstances it is possible to lose up to one dioptre of power by stopping reading and all other close work and by applying drugs that relax the eye for distant vision. Alternatively, if the cornea is flattened, then its power can also be reduced. This can be done in more than one way. Since the cornea is maintained in its curvature by pressure and the elasticity of its own tissues, deep cuts in its surface, allowing the tissue to expand, will cause a flatter curve to be formed. Such an operation is called Radial Keratotomy. It is relatively simple to carry out, but as it only corrects up to between three and four dioptres of myopia it is of little help to patients whose problems are more acute. However, since in most patients the scale of myopia is only between one and eight dioptres, Radial Keratotomy is of great interest.

It is not uncommon for a patient to ask his practitioner whether he would recommend surgery, almost as though such surgery was an obvious solution which the practitioner had momentarily overlooked. What are the risks? The answer is that, in the long term, we don’t know yet. The operation produces several scars on the cornea in areas away from its centre. While clear vision is not affected, in theory at least it should slightly decrease the cornea’s ability to collect light rays from its periphery.

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• How to Read Eyeglass Prescriptions
• Short-sightedness and the Environment part 3
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• Uncomfortable Eye, Computers and Eyestrain
• Eye Sight, Short- and Long-Sightedness
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• Eye Sight, Short- and Long-Sightedness continued
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