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REFRACTIVE ERRORS OF THE EYES

What with all the pollution, eye-stress due to reading in insufficient light, too much television (one might even humorously term this condition as the TV Syndrome) and the climatic conditions, no wonder we see an ever-increasing number of people suffering from refractive errors of the eyesight. Some progressive form of refractive errors is expected naturally in the 40+ age group when it is termed as presbyopia. This condition normally tends to stabilise by the age of 55. However, what is truly tragic is the fact that increasingly one comes across children and persons belonging to the younger age group sporting spectacles, most of which cannot be blamed on the process of fashion statement making of the young nor on the rays of the bright sun.

When one talks about refractory errors, one is referring to the condition where the person suffering from it requires a lens of some form to correct it. Such lenses may be in the form of spectacles, (and monocles, heaven forbid!), contact lenses or intra-ocular lenses (which are inserted into the eye and is carried out after a cataract operation, i.e. removal of the natural lens of the eye). The current discussion does not include the topic of cataracts.

The forms that such problems manifest is the complaint that one is unable to read as clearly as one did before. The problem, especially in children and young adults, falls under three principal categories. Too much television or studies could lead to a condition where the sufferer complains of "seeing double" or "haziness in the eyes" or eye fatigue which may or may not point towards a refractive error of the eye. It could be the result of tiredness of the eyes, or more particularly the eye muscles, and is usually relieved by some simple eye exercises, giving adequate rest to the eyes by reading less, improving the lighting conditions of the place where studies are undertaken and by restriction of television.

The three categories of refractive errors are myopia, hyperopia, and astigmatism.

  1. Also commonly known as short-sightedness, myopia is the condition where one can see things very clearly when placed close to the eye. However, things at a distance appear to be hazy, unfocused, or very poorly visible, all depending upon the severity of the condition. Such persons can do fine work which requires the hands being placed very close to the eyes while working as well as working with microscope.

  2. Also commonly known as far-sightedness, hyperopia or hypermetropia is a condition where things at a distance can be seen very well while as they are brought closer to the eyes they become progressively hazier. Such persons cannot perform fine work nor can they work well with microscopes unaided.

  3. Astigmatism is a condition which usually is detected on examining the eyesight. In some extreme cases the sufferer might complain of letters on the blackboard appears ‘slanted’ or ‘off centre’. The rays of light emanating from an object get focused on to the retina - the so called screen of the eye where the image is converted into electrical signals that are thereafter interpreted by the brain.

Myopia is mostly the result of a large eyeball as also a deformed cornea. Here the incoming rays of light get focused in front of the retina. A concave lens is used to bring the image into focus and thereby correct the error. When it presents in young persons, the condition is found to become progressively worse as the age increases. This is the result of the growth of the head, face, the eyeballs themselves as well as the increased deformity of the cornea. Hence we find a child suddenly requiring cylindrical lenses over and above the spherical ones. If the bad news is that the power of the lenses would progressively increase, the good news is that once the sufferer becomes a fully grown adult and stops growing, the strength of the lenses tends to remain static. Several ways of correcting the condition are available. First and the most frequently used means is by wearing a pair of spectacles. The second is to go in for contact lenses, though it must be stressed that wearing contact lenses does not automatically mean that no spectacles would be required at all since every corneal deformity is not totally corrected by contact lenses alone. The third option is to go in for a surgical procedure called ‘keratoplasty’ where a series of very precise cuts are made on the cornea with help of a diamond knife or the rays of excimer laser as is being increasingly done these days. Through the reshaping of the cornea the incoming rays of light into the eyes are forcibly focused onto the retina. This method is controversial and one can very easily find a doctor actively supporting this procedure while another next door who vehemently opposes it. One thing is certain. It works, though I cannot definitely state that this procedure is totally safe in the long run. The use of lasers has definitely made it better. Also, it works better in a person with a high degree of myopia than one with a lesser degree. Thus a person with a -10D lens sports a -1.5D lens after the operation while a person with a -1.5D lens still wears a -0.25D lens after. The parents of the myopic child nevertheless should be under no illusion. Myopia never gets cured as such. Please see below for some more elaboration on this point.

Hyperopia is mostly the result of a small eyeball. Here the incoming rays of light get focused behind the retina. A convex lens, much like the ones found in magnifying glasses, is used to bring the image in focus. When it presents in young persons, the condition is found to become progressively better as the age increases. This is the result of the growth of the head, face, the eyeballs themselves cause the eyeball to become larger and therefore the condition becomes self-correcting. The bad news is that the lenses of the spectacles are thick as they are essentially convex lenses - the same as that can be found in magnifying glasses. The complaint of eye fatigue in a young person may or may not be the forerunner of hyperopia itself. In those who have hyperopia the difficulty essentially lies in seeing things which are nearer to the eye, and if the condition is not too great, a young person may obtain a sharp and therefore clear image of an object placed closer to the eye performing more of a process called accommodation. This extra effort contributes towards the eye fatigue which typically occurs late in the evening, or after reading for a long time or after watching too much television. Again, the most frequently used means of correcting the error is by wearing a pair of spectacles. The other alternative is to go in for contact lenses. Since most of the sufferers would get cured, so to speak on their own as they grow older, surgery is not undertaken.

Astigmatism is almost exclusively the result of deformity of the cornea. It may however co-exist with other conditions, chiefly myopia. It also gets worse as the sufferer becomes older. The means of correction is the same as is for myopia.

No matter what, whenever any young person complains of difficulty in seeing things, it must be taken seriously and a proper ophthalmologist contacted without delay. Headaches are very rarely due to errors of refraction, they mostly are a result of the fatigue that sets in as the brain tries its level best to correct the visual error. So refraction errors are at best an indirect cause of headache. The advice, especially of wearing spectacles must never be trivialised and the young person must made to wear spectacles as soon as is possible and preferably at all times unless sleeping or bathing or washing face and eyes. All objections of the person must be overcome in this regard. It usually takes a little while for the person to get used to the eye-glasses, although I am not too sure how the young person concerned would react if informed of a ‘no television’ policy. A day without music on television filled with cool visuals, no viewing of the latest chartbuster, no cricket is not a day worth living for. That is the end of the civilisation as they know it. Such argument most often wins the day.

A further point to note is that should your child have large eyelashes, please tell the consulting ophthalmologist of the same so that while prescribing glasses the consultant dispenses a pair of lenses which are ‘clear off eyelashes’. Usually a good manufacturer of spectacles would be also be able to make the suitable pair of glasses if that person is informed about the long eyelashes while ordering the item. If the eyelashes get constantly brushed against the glasses, there is increased watering of the eyes, the glasses get dirty, the wearer becomes irritated and the visual capability gets impaired enough to render the wearing of the spectacles useless.

An alternative method is the use of contact lenses. With the advent of improved types of lenses, the rate of rejection (the wearer cannot use the contacts due to irritation that may even lead to injury to the eye) is becoming lesser than the usual 15% that was the norm before. Soft lenses are not good at all. Semi-soft are, while hard lenses are best if one can tolerate it (the tolerance levels for these lenses has historically been low though). Contact lenses have an additional advantage in being able to limit the increase in refractive errors. Since they are placed on the cornea and are essentially able to reshape the cornea so that the incoming rays of light are correctly focussed, they have been found to have some beneficial effect in the long run.

In conclusion, wearing glasses is not the end of the world. Considering the payoff between wearing them and letting the underlying condition get worse, the choice is indeed most limited. Contact lenses have proved a boon in more ways than one while the controversial surgery is increasingly gaining in popularity. The best person to advise is definitely the doctor concerned. Even though nature has provided two of these wonderful organs to us to view her, it is through the possession of both of them that mother nature can be fully appreciated to the fullest possible extent.

I would like add a few words about 'keratoplasty' here. It is definitely a revolutionary new technique for correction of refractive eye errors. These are carried out by making a series of precise cuts under anaesthesia on the clear part of the eye, called the cornea, in order to reshape it. The fundamental principle on which this procedure was based upon was that it was the loss of the round shape and correct curvature of the cornea that leads to errors of refraction. Initially the cuts on the cornea was made by hand using a very thin surgical blade. If the surgeon were to make too deep a cut on the cornea, it would have caused clouding of the cornea and ultimately loss of vision. This was precisely the reason why it was more known for the failures rather than due to the successes. Then came the age of lasers and further understanding of the procedure and principles and techniques involved in it. Today, the eye surgeon can make careful calculations about the degree of correction required and use computers to guide a laser ray to make the cuts. Since the length of the rays can be made extremely precisely, there is practically no danger of cutting too deep. Moreover, with computer-driven cutting, extremely precise cutting of the cornea is possible.

There are a few factors though that need to be considered. One, the technique has become more or less stable within the last 6-8 years (it has been around though for more than double that amount of time, at least) and hence one cannot be absolutely sure that the cornea, which is notorious for becoming hazy leading to blindness to various degrees even due to the slightest injury/infections, will not cloud in one's life time. I am a myopic, around -10 D, yet I will not undergo this surgery, at least for now. Two, such surgeries are most beneficial to persons who have high errors of refraction (more than +/-3 D) rather than ones who have less than this figure. Larger errors are easier to correct as the misshaping of the cornea is more pronounced and so the calculations for correcting them are more precise. It is the smaller errors that are difficult to measure as accurately. Three, if anyone thinks that after undergoing surgery one will not have to wear any glasses or contact lenses at all, then that person is in cloud cuckoo land. We all keep on growing till around 25 years of age. So unless you have passed this age, if you undergo the surgery, the face will grow and there will be a need to undergo further surgery or putting on glasses. This is because surgery corrects the error and not the underlying cause for the error. Four, the cost of the operation is high and be well aware that in most cases it is generally not covered by medical insurance.

The surgical techniques are improving and more innovative and effective methods are being constantly developed. So, please follow the advise of the medical doctor/ophthalmologist you can trust. It does make a lot of sense to ask around as to the experiences of persons who have undergone such treatment regarding the efficacy of the operation.

Legends - F = focal point where the rays of light converge to form the image

R = Retina, the place where the image is "read" and sent to the brain for identification

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Compiled from various sources by Dr. S. B. Bhattacharyya.
Copyright [SUDISA]. All rights reserved.
Revised: September 09, 1999.