In long-sightedness (hyperopia), close objects appear blurred because the light that enters the eye is focused behind the retina.
However, it is not possible for light to be focused behind the retina so the lens tries to correct this refractive error by changing its thickness (it becomes fatter). This process is called accommodation.
If you are long-sighted, it is not possible to accommodate fully, which means light cannot be sharply focused and vision will be blurred. This may occur if the:
- eyeball is too short
- cornea is not curved enough (it's too flat)
- lens is unable to become round enough
Long-sightedness can be caused a number of factors which are described below.
Age
Long-sightedness can occur at any age, but it is often more noticeable after the age of 40.
Age-related long-sightedness is known as presbyopia. It develops when the lens in your eye becomes stiffer.
Genetics
Long-sightedness is thought to be a condition that some people inherit from their parents.
However, with the exception of a rare form of hyperopia called nanophthalmos, specific genes for long-sightedness have yet to be identified and further research is needed.
Underlying condition
In rare cases, long-sightedness can be caused by other, underlying conditions including:
- diabetes
- microphthalmia (small eye syndrome) -where a baby’s eyes do not develop properly during pregnancy
- tumours around the eye (orbital tumours)
- foveal hypoplasia - where there is a problem with the blood vessels in the retina
