myopia or near sight

Myopia, or near sight, is the condition where the range of focus of the eye is shortened, making it unable to bring distant objects into focus. Some people are genetically more predisposed to myopia than others. Having two short-sighted parents will give a strong risk of developing myopia. The way an individual uses their eyes, as well as their genes, will determine how, or even if, they will become myopic. There are two processes involved in the development of myopia: emmetropization, which controls the growth of the rear of the eyeball and adult onset myopia, which controls the stretching of the central part of the eyeball.

Emmetropization: Moving Towards Normal Vision
While the eye grows, hormones control the growth of the rear part of the eye. These growth hormones are released in response to the degree of blur experienced when viewing a distant object. If the distance is too sharp then the eye deems itself too long sighted and growth is increased, lengthening the eye and shortening the sight. If the distance is too blurred then short sight is assumed and growth reduced at the back of the eye while the rest of the eye continues to grow, thereby lengthening the sight. This is called emmetropization, that is, seeking emmetropia, or normal vision. While the eye is growing, up to around 14 years old, it will tend to reduce refractive error (focusing problems) provided it is seeing the world directly, without lenses. Unfortunately this is rarely allowed to happen. The tendency has been for any refractive error measured in a child to be ‘corrected’ using lenses. The eye is then left to adapt to the world it sees through the lens, dutifully changing its shape to cancel out the prescription within a year or so. This results in stronger and stronger lenses being prescribed and is called progressive myopia. This tendency can be kept in check by allowing the eye to see the true distance (albeit blurred), without glasses and out of doors, even for just one or two hours a day.

Adult Onset Myopia To bring near objects into focus the circular ciliary muscle contracts allowing the lens to fatten providing the extra focusing power required. The ciliary muscle has two parts: the circular fibres controlling the lens and fibres that run along the eyeball itself spanning the part of the eye between the ciliary body and the beginning of the retina. These longitudinal fibres work in opposition to the circular fibres so that when the circular fibres are relaxed for distant focusing, the longitudinal fibres are tensed and when the circular fibres are tense for close focusing, the longitudinal fibres are relaxed. These longitudinal fibres have two functions: they help to tense the suspensory ligament for distant focusing and they control the elongation of the eyeball.The net result is that, in response to prolonged close focusing, the eyeball lengthens, shortening the sight. The eye gets better at the work it is used for. Unfortunately, as it gets better at doing close work it may lose the ability to focus the distance, creating myopia. This process is known as adult onset myopia although it can happen at any age.Once glasses are worn to bring the distance back into focus, the eye must work even harder overcoming the prescription in order to focus close up. This results in the myopia continuing to increase. This will happen to anyone who continues to do a lot of close work through a distance prescription.

What to do about myopia

There are various vision improvement systems for reducing myopia which have a common theme; relaxation of the eyes as well as the use of weaker than normal prescriptions. This makes sense, as both will help the eyes to be more distance focused. Many vision improvement practitioners now use Trayner pinhole glasses alongside their traditional exercises. The artificially small pupil provided by the Trayner Glasses encourages the eyes to focus beyond their habitual range, giving a more active encouragement to distance focus than is possible with the passive relaxation techniques.

Use Trayner pinhole glasses for at least half an hour at the end of the day to focus further away than you normally can (take out your lenses first). For some this will be reading, for others watching TV. This will leave your eyes more distance focused overnight. Avoid using your distance prescription for close work. For students who alternate between looking at the blackboard (distant) and their notebook (near), some opticians will now prescribe bi-focals.

For office workers, a reading prescription will stop the deterioration. This will be slightly weaker than your distance prescription allowing your eyes to stay more relaxed while you do close work. Wear this prescription as much as you can do safely. Use your distance prescription for driving. If you wear contacts you can wear the weakest reading glasses from the chemist over your standard lenses to make a reading prescription.©Peter Duthie 1998/2000