Refractive Power


Refractive power or optical power as it is sometimes known is the ability of the eye to bend light as it passes through the eye. It is most commonly measured in dioptres.

For a focussed image to be made on the retina, some parts of the eye must bend the light, so that it converges on a single point on the retina. The retina is responsible for detecting light and sending this information to the brain. If the image isn’t focussed on the retina, it becomes blurry, this is known as a refractive error.

The two major focussing components of the eye are the cornea and the lens. When we consider rays of light coming from an image, they hit the front of the eye, which is the cornea. This then causes the rays to begin to move towards each other, which is called converging. This same process then occurs at the lens, causing all the rays from the image to converge to a point on the retina. The power with which this process occurs is the refractive power, and is vital in producing clear images.

If the refractive power becomes too great or too small we see common problems such as long and short sightedness (myopia and hyperopia). It is possible for the eyes to have different refractive powers. This is known as anisometropia. These conditions can be rapidly corrected, either with spectacles or contact lenses, which help change the angle with which light rays enter the eye.


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