Myopia
Myopia is commonly known as “short-sightedness”. This occurs when the eyeball is relatively too long, and light rays are focused in front of the retina. Close objects appear clear but far objects cannot be seen clearly. To correct this, a minus (concave) lens is worn to focus light rays onto the retina, thereby allowing clear vision.
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Hyperopia
Hyperopia is commonly known as “far-sightedness”. This occurs when the eyeball is relatively too short, and light rays are focused behind the retina. Distant objects are slightly blurred, while near objects are more blurred. To correct this, a plus (convex) lens is worn to focus light rays onto the retina, thereby allowing clear vision.
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Astigmatism
Astigmatism occurs when the surface of the cornea is not uniform. This causes light rays to be brought to a distorted focus. Both near and distant objects are blurred. To correct this, a toric lens is worn to focus light rays onto the retina, thereby allowing clear vision. Astigmatism often occurs together with myopia or hyperopia.
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Presbyopia
Presbyopia occurs around the age of 40 when the focusing mechanism of the eye begins to become inefficient. Near objects begin to blur, and reading material have to be placed further and further away in order to be seen clearly.To correct this, reading glasses (plus power) are worn to help with near work. As the lens becomes less and less elastic over the years, higher power of reading glasses needs to be used. Reading glasses will help, however the power of the spectacles required may increase gradually with time.
The above refractive errors can be corrected by spectacles, contact contact lenses or LASIK
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