Wednesday, March 11, 2009 13:15


Normally our eyes work well, bringing an image of what we’re looking at into crisp focus on the retina at the back of the eye. Objects at different distances have to be brought into focus differently, and the way the eye changes its focus is by altering the shape of the lens inside it. Contrary to what most people imagine, most focusing is done by the cornea: the lens merely adds the finishing touches!

The lens is a squashy bag, stretched outwards by being attached round the whole of its circumference to a circular muscle, which is itself attached on its outer margin to the inside of the eyeball. When the muscle contracts it reduces the size of the central hole. This means that the lens isn’t pulled outwards as firmly. As a result, the tension on the lens slackens off, allowing it to change from being thin into being fat and bulky with a more highly curved surface. Because a fat and bulky lens bends the light more, when the lens is fat it can bring nearer objects into sharp focus on the retina. When the muscle relaxes the central hole opens, and there is a greater pull on the outside of the lens, causing it to become less globular and more disc-like.

However, sometimes we don’t focus quite as well as we would like. In older age, the pliability of the lens may be reduced so it can’t focus properly and you may need glasses to see for both distances and close-up. Secondly, because of the way the physics of focusing works, those with slightly smaller eyes tend to be long-sighted, and those with bigger than average eyes, short-sighted.

In addition, the lens or cornea may not be perfectly symmetrical, in which case astigmatism occurs. This means that the eye can’t focus on both vertical and horizontal lines at the same time, further, because of the physics of light and lenses, focusing is more critical if the aperture of the lens is large. This makes it harder to focus in dim conditions, when the pupil of the eye opens and more of the lens is used to collect light. A slightly short-sighted person may find that he can focus on distant objects in bright light, but cannot in dim light. By experience we soon find out that we can see slightly better by half-shutting our eyes and peering. This, of course, tenses up all the muscles round the eye and can cause headaches.

Constantly refocusing the lens also causes discomfort. If the muscles of the lens are constantly altering focus, they will become fatigued, especially in the case of astigmatism. Just as tiring are the effects of trying to focus on an object that is just outside the normal focusing ability of the eye. The extra muscular effort that we use on these occasions can cause considerable discomfort and pain in the eyes -the so-called ‘eye strain’. This is usually much worse after long periods of reading or other close work, and goes away after a period of rest, when the eyes are used for less concentrated activities. The ache can be in the eyes, in the forehead, or in the temple.

A quick way to check whether this is happening to you is to look at a book at your normal reading distance and then bring it towards you until it’s about half as near. If you feel pain in your eyes when you try to look at the printing at the nearer distance, then you may well be suffering headaches due to eye strain.

People who are short-sighted usually have no difficulty in close work and reading, and it is interesting that the pain of eye strain usually affects only those who are long-sighted, or who have astigmatism. Pain usually occurs only where there are minor eye problems, because only this type of problem can be removed by muscular activity.

Finally, eye strain also occurs if your glasses are no longer right for you; perhaps they are over-strong, or else you’ve had them a long time and they’re too weak. You may also find your eyes aching the first time you use new glasses, but as you get used to them this should go away – by the end of about a week. If the discomfort persists, check with your optician that your glasses have been made to the correct prescription.

Don’t forget, too, that eye-sight can change quite rapidly. Regular visits to the optician are the only way to be sure that your glasses are still appropriate.

The treatment for these eye defects is quite simple; make sure that you go to an optician regularly and, if necessary, obtain spectacles.

Complementary treatment

There are a number of tried and tested home remedies for eye-strain. Try lying down with a cucumber slice on each eye which is cooling and refreshing. A camomile tea compress or rinse eases painful eyes and eye muscles. Witch hazel can be used as a compress for strained eyes. Rosehip teabags over the eyes for fifteen minutes relieves strain.

You can also take eyebright internally to strengthen eyes. Ruta, a homoeopathic remedy, may help relieve eye-strain after reading, etc. Arnica, nat mur or phosphorus may also be suggested.

Relaxation will help ease eye-strain.

Rubbing your temples with jasmine, camomile or lavender essential oils will relieve headaches caused by eye-strain. Shiatsu can ease tired and swollen eyes.


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