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Refractive Errors |
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Refractive errors results in decreased vision, when the eye can not point focus the image of an object on the retina.
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Myopia, hyperopia, astigmatism
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Myopia(nearsightedness) happens when the light rays are focused before they reach the back of the eye. (nearsightedness). Hyperopia (farsightedness) happens when the incoming light rays are not focused on the retina when they reach the retina.
In the case of “astigmatism,” one or more surfaces of the cornea or lens (the eye structures which focus incoming light) are not spherical (shaped like the side of a basketball) but, instead, are cylindrical or toric (shaped more like the side of a football). As a result, there is no distinct point of focus inside the eye but, rather, a smeared or spread-out focus. Astigmatism is the most common refractive error.
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| Presbyopia
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After age 40, sometimes noticeable even before 40, especially in hot climates like India, the human eye is affected by presbyopia. This causes a decrease in maintaining the clear focus at close distance and results in difficulty with reading small print.
Presbyopia is caused by a loss of flexibility of the crystalline lens, and also as a result of weakening of the ciliary muscles which control lens focusing. This is a natural condition attributable to the aging process.
All the above refractive errors can be corrected by glasses, contact lenses, and laser surgical procedures like LASIK, Conductive keratoplasty (presbyopia). |
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