When viewing an object that is far away, the eye – if we are perfectly sighted – is shaped so that the object is clearly focused on the retina. This means that the image is clear. When we look at something close up, for example reading a book, the muscles inside the eye that surround the lens contract to make the lens change shape. This focuses the light from the book onto the retina.
The lens inside a child’s eyes is elastic, and so will naturally alter its shape easily to allow for a change in focus from a distant to near object. As we get older however, the lens will stiffen and so change shape less easily. This means that the distance up to which we are able to focus becomes longer and we are no longer able to focus on things that are close to us, having to hold them further away to see them clearly. This is more noticeable with very close work, for example, when threading a needle. It can also mean that it may take longer for us to focus from looking at something close up to looking at something far away (or vice versa).
This change in focusing tends to become more noticeable when we reach our late thirties or forties as we then find it difficult to focus on things that are at the normal reading distance. It is quite common to see people who are presbyopic holding things away from them in an attempt to see them clearly. As this affects things that are close to us first, our vision of things that are further away – such as the computer – is not affected until later, when the lens has lost almost all of its elasticity.
This loss in elasticity is corrected with spectacles. This may mean having separate pairs for distance and reading and maybe for middle distance such as looking at the computer or reading sheet music.
What is the treatment for presbyopia?
Presbyopia is a natural part of ageing and there is no cure for it. The solution is generally to wear glasses for reading. Because reading glasses focus light from close objects, it is normal to find that distant objects are blurred when looking through them. They can either be removed for distance viewing or alternatively, bifocal or varifocal lenses can be used.
Bifocal lenses consist of two separate areas of the lens which are separated by a line: the top part of the lens focuses light from distant objects, and the bottom part of the lens focuses light from near objects. Varifocal lenses work in a similar way to bifocal lenses but without a visible line on the lens. This is because the power gradually changes from the top to the bottom of the lens, to allow objects at any distance to be seen clearly, simply by moving the head up and down to look through a different part of the lens.
Are there exercises I can do to stop needing reading glasses?
Presbyopia is not caused by muscle weakness but by the lens stiffening as we age. There are no exercises that can help this.
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