Short sight occurs when light is focused in front of the retina causing distance vision to become blurred. Near vision, however, is usually clear. Short sight normally develops in childhood or adolescence and is often first noticed at school. Glasses may need to be worn all the time or just for driving, watching TV or sports.
Astigmatism occurs when the front part of the eye, the cornea, is not a regular symmetrical spherical shape. Instead, its shape is rather like that of the back of a spoon - longer in one direction than another. Because the cornea is an irregular shape, the eye can't focus light passing through it sharply on to the back of the eye or retina therefore vision can be blurred at all distances.
Who's affected? Astigmatism is common and is usually present from birth. Most people have slight astigmatism - it's rare for the cornea to have developed in a perfectly symmetrical way. But in mild cases, the eye can adjust to focus light adequately.
What are the symptoms? In severe astigmatism, vision is blurred or distorted whether the person is reading close up or looking further into the distance.
In milder cases the person may complain their vision is blurred at certain distances, that they have tired or dry eyes, that it's a struggle to focus or read, or that they have headaches, especially when trying to focus.
In most cases, astigmatism can be corrected by wearing properly fitted spectacles or contact lenses. Milder astigmatism may not need treatment unless the person is doing a job that puts intensive demands on the eyes, for example, computer work, reading, or if they have headaches, especially when trying to focus.
Long sight occurs when light is focused behind the retina rather than on it, and the eye has to make a compensating effort to re-focus. This can cause discomfort, headaches or problems with near vision. Glasses may need to be worn all the time or just for close work, such as reading, writing or computer use. In older people, as re-focusing becomes more difficult, distance vision may also become blurred.
Presbyopia is the loss of focusing ability that occurs naturally with age. In younger people, the lens is very flexible and the eye has a wide range of focus from far distance to close up. As you get older, the lens slowly loses its flexibility leading to a gradual decline in ability to focus on near objects.
Presbyopia is not a disease but a normal and expected change which sooner or later affects everyone, whether or not you already wear glasses or contact lenses.
Around the age of 40-45, you will begin to notice that you are holding the newspaper further away or need more light to read small print. There is no advantage in delaying using reading glasses, or changing to bifocals or varifocals. They will not make the eyes lazy. Your optometrist will advise you on the best form of vision correction to suit your individual lifestyle and occupation.
Find out more about lenses to correct presbyopia.