Contact lenses are made use of for vision correction and are placed on the cornea of the eye. They do the identical corrective function that traditional spectacles, or glasses, do. Having said that, in comparison, they are really light in weight and are, for all purposes, invisible. Make contact with lenses help kind the image on the retina of the eye by either converging or diverging the rays of light getting into the eye.
Earlier speak to lenses have been made of glass, and have been scleral lenses. Scleral lenses are massive get in touch with lenses that cover the comprehensive sclera – the white outer coating – of the eye. These unwieldy lenses could only be worn for a short period at a time. With the development of PPMA – polymethyl methacrylate – in the 1930s, plastics have been initially employed in speak to lenses. These had been in fact, hybrid scleral lenses, produced with the mixture of each, glass and plastic, in 1936.
By the 1950s, substantially smaller sized make contact with lenses had been created that covered only the cornea of the eye and not the whole eye.
Sorts of Vision Impairments
One of the significant uses of contact lenses is to right visual defects. The common impairments are Myopia, Hyperopia, Astigmatism, and Presbyopia.
Myopia – is a visual disability where the image of the object observed is formed in front of the retina. Throughout this visual impairment, one can see objects that are close to, and not the distant objects, which appear blurred. This defect is also recognized as nearsightedness. This is a pretty popular impairment, with more than 25 % of the adults in the United States suffering from it. The defect can be corrected by the use of concave get in touch with lenses.
Hyperopia – It is also recognized as Hypermetropia, and the image of the object is formed behind the retina. Far objects can be observed clearly, and the close to objects seem to be blurred. Hyperopia is far more usually identified as farsightedness, and extra than 13 % of the children in the United States, in the age group 5 to 17, suffer from it. The defect can be corrected by the use of convex speak to lenses.
Astigmatism – This takes place when the lens of the eye has much more than one particular focal point, in distinctive meridians. Astigmatic people today cannot see in fine detail, and have to have cylindrical lenses to right their impairment. Nearly 34 % of American young children in the age group five to 17 have this impairment.
Presbyopia – This is an impairment, which comes with age, usually soon after the age of 40. The impairment develops as the lens of the eye loses its elasticity. Bifocal speak to lenses are used to right this vision defect.
Lenses Utilized For Vision Correction
In the case of typical vision, the light from the object hits the cornea and focuses on the retina. Due to some refractive error, at times the light from the object does not focus on the retina, but either in front of it, or behind it. To correct this refractive error, make contact with lenses are employed to focus on to the retina.
The sort of get in touch with lenses utilized depends on the type of vision impairment, and how significantly refractive error is involved. How much the lens bends the light to concentrate on the retina is measured in diopters (D).
Myopia happens when the light is focused in front of the retina, as the eyeball is longer than standard. To correct this impairment, which is also identified as nearsightedness, a concave lens is employed. This lens is thinner at the center, and assists move the focus ahead, towards the retina.
To correct this vision impairment, the curvature in the concave make contact with lenses is determined by the measurement in diopters. The larger the quantity of diopters, bigger is the vision defect. In myopia, the diopter number is preceded by a minus (-) sign, denoting that the concentrate is brief of the retina.
In the case of hyperopia, the light is focused beyond the retina. Hyperopia is also recognized as farsightedness, as distant objects are seen clearly in this impairment. colored contact lenses is shorter than normal, and a convex lens is utilized to appropriate this vision defect. The make contact with lens used is thicker in the center, and helps move the concentrate back onto the retina.
In this case, too, the curvature necessary in the convex contact lenses is determined by the measurement in diopters. The diopter quantity is preceded by the plus (+) sign, denoting that the focus is beyond the retina.
The lenses applied for the correction of myopia and hyperopia are categorized as spherical speak to lenses.
When the cornea is irregularly shaped, the light from the object falling on the cornea focuses on far more than 1 point. This distortion of the image is called astigmatism. Unique lenses have to have to be developed, primarily based on the individual’s distortion of image. These lenses are known as toric lenses.
Even though toric lenses are produced of the exact same supplies as the spherical lenses, they are especially developed to suit person impairments. These lenses have distinctive curvatures, thicker in some areas, and thinner in other folks. These lenses are developed to right astigmatism and myopia or hyperopia, if required.