Contact lenses are used for vision correction and are placed on the cornea of the eye. They’ve been intensively developed and modified over the years become the most effective and comfortable they can be. Here’s all you need to know about contact lenses:
These are the types of vision impairments that call for the use of corrective lenses:
It is a visual disability where the image of the object seen is formed in front of the retina. This causes near-sightedness: the inability to see distant objects clearly.
It is also known as Hypermetropia, and the image of the object is formed behind the retina. Far objects can be seen clearly, and the near objects appear to be blurred.
This happens when the lens of the eye has more than one focal point, in different meridians. Astigmatic people cannot see in fine detail and need cylindrical lenses to correct their impairment.
This is an impairment in which the lens of the eye loses its elasticity. Bifocal contact lenses are used to correct this vision defect.
The type of contact lenses you need depends on the type of vision impairment, and how much refractive error there is. How much the lens bends the light to focus on the retina is measured in diopters (D).
To correct Myopia, a concave lens is used. This lens is thinner at the center, and helps move the focus ahead, towards the retina. The curvature in the concave contact lens is determined by the measurement in diopters. The larger the number of diopters, the more severe the vision defect. In myopia, the diopter number is preceded by a minus (-) sign, denoting that the focus is short of the retina.
In the case of Hyperopia, a convex lens is used to correct this vision defect. The contact lens used is thicker in the center and helps move the focus back onto the retina. The curvature required in convex contact lenses is determined by the measurement in diopters. The diopter number is preceded by the plus (+) sign, denoting that the focus is beyond the retina.
The lenses used for the correction of myopia and hyperopia are categorized as spherical contact lenses.
Toric lenses are used to correct Astigmatism and must be custom made to accommodate the specific areas of error in a patient’s eye. Though toric lenses are made of the same materials as the spherical lenses, they are specifically designed to suit individual impairments. These lenses have different curvatures, thicker in some places, and thinner in others.
For the correction of Presbyopia, special bifocal lenses are required as the person suffering from it needs correction for both Myopia and Hyperopia. In such lenses, either the correction for near impairment is placed in the center of the lens, with the distant correction on the outside, or vice versa.
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