As we get older the flexibility of the lens inside your eye reduces. This is called Presbyopia.
This means that you are less able to focus on things that are close to you, so you may need reading glasses. When you look at something close up, for example a book, the muscles inside your eye surrounding 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 eye is elastic so can change shape easily. As we get older the lens naturally stiffens and so it changes shape less easily.
This means we are no longer able to focus on things close to us, having to hold things further away to see things clearly. This change tends to happen in your late thirties or forties. Due to the fact your lens has lost its elasticity when you are presbyopic, you will need glasses to focus on different distances. This may mean separate pairs for distance and reading and maybe for middle distance such as looking at the computer or reading music.
This is a natural part of ageing and there is no cure for it. The solution is generally to wear glasses for reading. Your reading glasses focus the light coming from objects close to you, you will find if you wear them and look at something far away it will appear blurred. This is quite normal and you will often see people peering over their reading glasses to see clearly in the distance. If you do not want to do this or prefer not to have a separate pair of reading glasses, the alternatives are bifocal or varifocal lenses.
Also, it is common to find that things are more blurred without your specs in dim light. This is due to your pupils getting bigger in dim light and you have less depth of focus, causing you to notice the blurriness more. The same can happen at night, when you are tired and the muscles find it more difficult to change the shape of the lens. The opposite is true in bright light, you will often find you can see better in bright light, for example in the sunshine, when your pupils will become smaller. This increases your depth of focus and the blurriness isn’t as noticeable.
Presbyopia will get worse as you age, until you reach your late fifties, when you will have no natural focusing ability left. Unfortunately, there is nothing you can do to stop it.
Many shops sell ready made reading glasses, but these are only correct for you if both eyes have the same prescription, and you have no astigmatism. They are often not made to the same standard as prescription glasses.
Even if you are using ready made reading glasses, it is still important to visit your opticians regularly as people over 40 are more at risk of eye diseases such as glaucoma and age-related macular degeneration.