Contact lenses in physics

Ingrid S. Forestier Román

Lenses have curved surfaces, or a very large number of flat surfaces located at slightly different angles. Converging lenses which are positive lenses are thicker at the centre than at the edges. Diverging lenses which are negative lenses are thicker at the edges than at the centre. Contact lenses go beyond a vision correction. They are very helpful for the eye because by converging or diverging the rays of light that enters the eye they form the image on the retina.

The eye works like a camera with two lenses, absorbing and processing light reflected from your surroundings. Light first passes through the cornea. Like a camera lens, it refracts light, helping to focus the light. The light then passes through the pupil, like the aperture in a camera, the pupil controls the amount of light entering the eye by becoming larger or smaller. The light then passes through the eye's natural crystalline lens. The natural crystalline lens "fine-tunes" the image before it is focused on the retina at the back of the eye. The retina works like the film in a camera. The retinal nerves absorb light and convert it into electrical signals. These signals are subsequently sent through the optic nerve to the brain where they are interpreted as visual images. If both lenses are working properly, the light is focused precisely on the surface of the retina. If the two lenses are not working properly, clear vision may be achieved by refocusing light rays with the use of corrective lenses.

There exist different types of impairments that could be corrected with convex or concave lenses. Myopia is a visual disability where the image of the object seen is formed in front of the retina. In this impairment, one can see objects that are near but those that are distant one cannot. Myopia is a very common impairment that can be corrected by the use of concave contact lenses, lenses that are thinner in the center than on the edges increasing the focal length.. Hyperopia or also known as hypermetropia is where the image of the object seen is formed behind the retina. In this case one can distinguish far objects but the one near appear to be blurred. This defect can be corrected by the use of convex contact lenses, lenses that are thicker in the center than on the edges decreasing the focal length. . Another very common impairment is the astigmatism, it happens when the lens of the eye has more than one focal point. Persons with this visual disability cannot see clearly and detailed, that is why they need cylindrical lenses to correct their impairment. Last but not least is Presbyopia, is an impairment that develop with age because the eye loses its elasticity. Contact lenses used to correct this vision defect are bifocal, bifocal or multifocal lenses have two or more different curves or shapes combined into one lens. Usually the bottom of the lens is for reading or viewing close objects, while the top of the lens is for seeing farther into the distance.

As mentioned before, type of contact lenses used depends on the type of vision impairment one have, and how much refractive error is involved. To know how much the lens bends the light to focus on the retina, Scientifics measured it in diopters (D).