Three Common Vision Problems

Focus

To perceive the world accurately, it is required that the visual image is focused on the retina. In a lot of people this (no longer) works well, resulting in the need to wear glasses. The cornea and the lens focus the image on a wrong focal point. This article discusses three common problems with vision:

• Shortsightedness, or myopia
• Farsightedness, or hyperopia,
• Presbyopia.

Fig. 1: The Human Eye (source: http://www.freedomscientific.com/resources/vision-anatomy-eye.asp)

Shortsightedness or Myopia

When the stretched out lens results in a focal point in front of the retina, a person will have trouble seeing far away objects sharply. The light waves from adjacent point will overlap, causing a blurry image. Objects close by will cause no such problem, as the focal point here lies further backwards in the eye.

People who experience difficulties in seeing objects at a distance, but not with watching objects close by, suffer from shortsightedness or myopia. The solution here are concave glasses, or contact lenses, as these decrease the convergence of the light waves, pushing the focal point backwards. Another option is a laser treatment that makes the cornea flatter.

Fig. 2: Myopia (source: http://www.condronoptical.co.uk/your-eyesight-explained)

Farsightedness or Hyperopia

If the lens cannot be made spherical enough to get the focal point of close by objects on the retina, the diagnosis is farsightedness or hyperopia. People with hyperopia have no problems with seeing far away objects, but the focal point cannot be brought forward enough to see close by objects sharply. As the light waves are not focused on the retina, they will overlap, resulting in a blurry image of objects close by.

The solution to this problem are convex glasses or contact lenses, or a laser treatment that makes the cornea more spherical, pushing the focal point forward.

Fig. 3: Hyperopia (source: http://www.condronoptical.co.uk/your-eyesight-explained)

Presbyopia

A specific form of farsightedness, known as presbyopia, commonly occurs in people from age 40 onwards. As people age, the inside of the lens hardens, making it harder for the lens to be brought into a spherical shape, leading to difficulties in focusing on nearby objects. As this hardening process progresses with age, the closest point at which one can see an object sharply will continue to increase.

Convex glasses or lenses, or laser treatment making the cornea more spherical, help in this situation, as the need for the lens has to be less globular to focus.

References

• Cline, D.; Hofstetter, H.W. & Griffin, J.R. (1997). Dictionary of Visual Science. Butterworth-Heinemann.
• Heys, K.R.; Cram, S.L. & Truscott, R.J.W. (2004). Massive increase in the stiffness of the human lens nucleus with age: the basis for presbyopia? Molecular Vision. 10, pp. 956 – 963.