Eye Care Blog

Of all our faculties, sight has consistently been considered the most miraculous, the most beneficial. In a moving passage from his correspondence, Charles Darwin refers to a time when ‘the thought of the eye made me cold all over’. And with good reason: for when, in 1859, he first published Origin of Species, by far the commonest objection to his revolutionary theory of evolution by natural selection was that a process so dependent upon chance and accident could not possibly account for such an intricate— and beautiful! — organ. And even today, when there is so much evidence collected in support of Darwin’s views, it still requires almost an act of faith for the non-biologist to accept that the complicated mechanisms that allow us to ’see’ the world are really no more than the outcome of random genetic mutations, over however many hundreds of millions of years. We are so conditioned to thinking of life in essentially pictorial terms that we can only with difficulty imagine that remote past when life first stirred but was not seen.

But biology, though it may have changed man’s understanding of organic creation, has not in any way diminished the pre-eminence attached to sight. Rather the reverse: for biology shows us that the eye is, quite literally, a part of the brain, the place, if you like, where the brain rises to the surface. We see with, not through, our eyes. But because they are such complex mechanisms they are peculiarly liable to defect, breakdown and injury. And yet, because we use them continuously and in so many different contexts we insist that they perform to a very high standard. We have devised ways of measuring that performance with a precision that is entirely lacking in our measurement of hearing, taste, smell or touch. Not surprisingly, therefore, many people have ‘bad eyes‘: modern society is on the active look-out for them, in a way it is not on the look-out for poor hearing, poor smell, poor touch. Equally, modern civilization also places an unprecedented strain on the optic system of the ordinary person. Television screens, artificial lighting, abundant reading materials, bad diet, tobacco, alcohol, even some of the drugs used in medicine, can all contribute to individual cases of deteriorated vision.

But the industrial environment is by no means entirely to blame. In addition to the possible causes of bad sight just mentioned there are a host of natural agents of optic degeneration to be accounted for as well: genetic abnormalities, viruses, entropy. The wonder of it is, perhaps, that the number of people who suffer serious disorders is as few as it is. But the eye is not only intricate and delicate: it is also well-made, nature’s finest artefact, and comes equipped with several sturdy defence mechanisms.

We examine the different sorts of problem that may arise, and the different parts of the eye that may be affected. But before we turn to these matters it would be well to give a general account of the normal eye, and its passage from birth to old age.

In general terms organs develop in accordance with the needs of the host body. Thus, the newborn baby does not necessarily have good vision during the first hours or even weeks of its life. Because of the sacrosanctity of human life, not a very great deal of research has been done in this area, but studies of our nearest kin in the animal kingdom, the primates (apes and monkeys), have shown that good vision depends upon certain brain cells developing at a site best considered as a relay station. These ‘bells help process information gathered by the eye as it travels toward the ‘visual cortex’, i.e. that part of the brain which is responsible for recoding visual data (tiny electronic impulses) into ‘pictures’. If these cells are destroyed then the primate concerned will be blind. But the evidence suggests that the complete development of these cells, among primates, does not occur until a few minutes after birth, so that, even if at the moment of birth the eye itself were capable of perfect vision, the machinery for receiving its data is still on the assembly line.

As far as we know humans follow roughly the same schedule as apes and monkeys. It is known, however, that some other animals take a relatively longer time to establish ‘neural pathways’ from the eye to the cerebral cortex. Among cats, for example, there is usually a delay of around six weeks before vision is developed. Some interesting recent experiments with kittens shows that if they are kept ‘blindfolded’ for six weeks or less there will be no impairment in their subsequent visual acuity; but if they are blindfolded for more than six weeks there will be an impairment, and the severity of this will depend on the total period of deprivation. On the other hand, kittens that are blindfolded after the visual cortex has been fully activated, that is, after a period of about twelve weeks, are not seriously affected

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