| Contact lenses are used for vision correction and | | | | bends the light to focus on the retina is measured |
| are placed on the cornea of the eye. They do the | | | | in diopters (D). |
| same corrective function that conventional | | | | Myopia occurs when the light is focused in front |
| spectacles, or glasses, do. However, in | | | | of the retina, as the eyeball is longer than normal. |
| comparison, they are very light in weight and are, | | | | To correct this impairment, which is also known |
| for all purposes, invisible. Contact lenses help form | | | | as nearsightedness, a concave lens is used. This |
| the image on the retina of the eye by either | | | | lens is thinner at the center, and helps move the |
| converging or diverging the rays of light entering | | | | focus ahead, towards the retina. |
| the eye. | | | | To correct this vision impairment, the curvature in |
| Earlier contact lenses were made of glass, and | | | | the concave contact lenses is determined by the |
| were scleral lenses. Scleral lenses are large | | | | measurement in diopters. The larger the number |
| contact lenses that cover the complete sclera | | | | of diopters, larger is the vision defect. In myopia, |
| – the white outer coating – of the | | | | the diopter number is preceded by a minus (-) |
| eye. These unwieldy lenses could only be worn | | | | sign, denoting that the focus is short of the retina. |
| for a short period at a time. With the | | | | In the case of hyperopia, the light is focused |
| development of PPMA – polymethyl | | | | beyond the retina. Hyperopia is also known as |
| methacrylate - in the 1930s, plastics were first | | | | farsightedness, as distant objects are seen clearly |
| used in contact lenses. These were in fact, hybrid | | | | in this impairment. The eyeball is shorter than |
| scleral lenses, made with the combination of both, | | | | normal, and a convex lens is used to correct this |
| glass and plastic, in 1936. | | | | vision defect. The contact lens used is thicker in |
| By the 1950s, much smaller contact lenses were | | | | the center, and helps move the focus back onto |
| developed that covered only the cornea of the | | | | the retina. |
| eye and not the whole eye. | | | | In this case, too, the curvature required in the |
| Types of Vision Impairments | | | | convex contact lenses is determined by the |
| One of the major uses of contact lenses is to | | | | measurement in diopters. The diopter number is |
| correct visual defects. The general impairments | | | | preceded by the plus (+) sign, denoting that the |
| are Myopia, Hyperopia, Astigmatism, and | | | | focus is beyond the retina. |
| Presbyopia. | | | | The lenses used for the correction of myopia and |
| Myopia - is a visual disability where the image of | | | | hyperopia are categorized as spherical contact |
| the object seen is formed in front of the retina. | | | | lenses. |
| During this visual impairment, one can see objects | | | | When the cornea is irregularly shaped, the light |
| that are near, and not the distant objects, which | | | | from the object falling on the cornea focuses on |
| appear blurred. This defect is also known as | | | | more than one point. This distortion of the image |
| nearsightedness. This is a very common | | | | is called astigmatism. Special lenses need to be |
| impairment, with over 25 percent of the adults in | | | | designed, based on the individual's distortion of |
| the United States suffering from it. The defect | | | | image. These lenses are known as toric lenses. |
| can be corrected by the use of concave contact | | | | Though toric lenses are made of the same |
| lenses. | | | | materials as the spherical lenses, they are |
| Hyperopia - It is also known as Hypermetropia, | | | | specifically designed to suit individual impairments. |
| and the image of the object is formed behind the | | | | These lenses have different curvatures, thicker in |
| retina. Far objects can be seen clearly, and the | | | | some places, and thinner in others. These lenses |
| near objects appear to be blurred. Hyperopia is | | | | are designed to correct astigmatism and myopia |
| more commonly known as farsightedness, and | | | | or hyperopia, if required. |
| more than 13 percent of the children in the United | | | | For the correction of presbyopia, special bifocal |
| States, in the age group 5 to 17, suffer from it. | | | | lenses are required, as the person suffering from |
| The defect can be corrected by the use of | | | | it requires both correction for nearsightedness and |
| convex contact lenses. | | | | farsightedness. In such lenses, either the |
| Astigmatism - This happens when the lens of the | | | | correction for near impairment is placed in the |
| eye has more than one focal point, in different | | | | center of the lens, with the distant correction on |
| meridians. Astigmatic people cannot see in fine | | | | the outside, or vice versa. |
| detail, and need cylindrical lenses to correct their | | | | Types Of Contact Lenses |
| impairment. Nearly 34 percent of American | | | | The initial lenses were rigid lenses that did not |
| children in the age group 5 to 17 have this | | | | absorb water. This kept the oxygen from passing |
| impairment. | | | | into the cornea of the eye, causing eye irritation |
| Presbyopia - This is an impairment, which comes | | | | and other discomforts. |
| with age, generally after the age of 40. The | | | | Then came the soft contact lenses made from |
| impairment develops as the lens of the eye loses | | | | hydrogel, which allowed oxygen to pass through |
| its elasticity. Bifocal contact lenses are used to | | | | them to the cornea. These lenses came to be |
| correct this vision defect. | | | | known as ‘breathable' contact lenses. This |
| Lenses Used For Vision Correction | | | | made it possible for contact lenses to be worn |
| In the case of normal vision, the light from the | | | | comfortably and for longer periods. Today, there |
| object hits the cornea and focuses on the retina. | | | | are: |
| Due to some refractive error, at times the light | | | | Daily wear lenses, which are removed at night. |
| from the object does not focus on the retina, but | | | | Extended wear lenses that can be worn for |
| either in front of it, or behind it. To correct this | | | | extended periods without removing. |
| refractive error, contact lenses are used to focus | | | | Disposable lenses that can be discarded after a |
| on to the retina. | | | | day, a week, or a few weeks. |
| The type of contact lenses used depends on the | | | | In addition, there are color contacts, which are for |
| type of vision impairment, and how much | | | | cosmetic purpose. |
| refractive error is involved. How much the lens | | | | |