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REFRACTIVE ERRORS


The most common cause of blurred vision is refractive errors. Refractive errors result from abnormality of either the length of the eyeball or curvature of the front surface of the eye called the cornea. Refractive errors can be due to either hereditary or developmental influences. When a refractive error exists, the image is not in focus. Four situations can arise;

1)

Shortsightedness or myopia The image is focused in front of retina because the eyeball is either too long or the cornea too curved. The person can see near objects but distant objects appear blurred. This is the most common refractive errors in Asians and usually manifests at the age of 10 to 18 years.

2)	Long-sightedness or hypermetropia The image is focused behind the retina because the eyeball is too short or the cornea too flat. The person can see distant objects but near objects appear blurred.

3)	Astigmatism The image is not focused as 1 image point on the retina and objects at all distances appear blur and distorted. Astigmatism is due to unevenness of the cornea surface.

4)

Presbyopia Presbyopia is part of the aging process and usually occurs after the age of 40 years. The normally elastic lens, which acts as an auto-focus mechanism, becomes hardened with age and can no longer focus on near objects. Near work and reading becomes a problem. Although it may be possible to hold the object further away to keep it in focused, eventually reading glasses or bifocal spectacles will be necessary to treat the condition.