Long-sightedness - Causes 

Causes of long-sightedness 

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How the eye works

The parts of the eye that help you to see are:

  • the cornea – the transparent layer at the front of the eye
  • the lens – the transparent crystalline structure that focuses light on to the retina
  • the retina – the light-sensitive layer that lines the interior of the back of the eye
  • the optic nerve – which transmits images from the retina to the brain

Light enters the eye through the cornea. The light rays pass through the lens and are focused onto the retina as an image. The retina converts the image into electrical signals, which are then transmitted to the brain by the optic nerve.

If a person suffers from long-sightedness (hyperopia), close objects appear blurred because the light that enters the eye is focused behind the retina, instead of on it.

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

As it is not possible for light to be focused behind the retina, the lens tries to correct this refractive error by changing its thickness, becoming 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.

Long-sightedness can be caused by several 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



Page last reviewed: 09/07/2014

Next review due: 09/07/2016

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