Physics of contact lenses
Contact lenses are used for visual acuity and are placed on the cornea of the eye. The same correction function is used as traditional eyewear or glasses. For comparison, however, they are very light and invisible in all respects. Contact lenses help the image in the retina of the eye or the approximation or deviation of the eye's incoming light beams.
Earlier contact lenses were made of glass and had scleral lenses. Scleralian lenses are large contact lenses that cover the entire whiteness of the eye – the white outer coating. These cumbersome lenses can only be worn briefly. By developing the PPMA polymethyl methacrylate, plastic materials were first used in contact lenses in the 1930s. They were actually hybrid scleral lenses, both in combination with glass and plastic, in 1936. During the 1950s, much smaller contact lenses were developed, which only revealed the cornea of the eye and not the whole eye.
Types of vision reduction
One of the main areas of use of contact lenses is the correction of visual defects. General damages are Myopia, Hyperopia, Astigmatism and Presbyopia.
- Myopia – visual disability where the image of the seen object is visible to the retina. In this vision impairment, you can see objects that are close to you and not the distant objects that look obscure. This shortcoming is also called short-sightedness. This is a very common disruption since more than 25 percent of adults in the United States suffer from it. The fault can be corrected with concave contact lenses.
- Hyperopia – Hypermetropia is also known and the image of the object is formed behind the retina. Farther objects are clearly visible, and nearby objects seem obscure. Hyperopia is more frequent than distance, and in the United States, more than 13 percent of children aged 5 to 17 are suffering. The error can be corrected by convex contact lenses.
- Astigmatism – This happens when the eyepiece has more focal points in different meridians. Astigmatic people are not visible in fine detail and need cylindrical lenses to correct damage. In the age group of 5 to 17 years, nearly 34 percent of American children have such a disability.
- Presbyopia – This is a disability that is associated with age, usually after age 40. Impairment develops as the eyepiece loses its elasticity. Bifocal contact lenses are used to correct visual impairment.
Lenses used to improve vision
In normal vision, the light of the object reaches the cornea and focuses on the retina. Because of some failure, sometimes the object's light does not focus on the retina, but before or behind it. To correct the refraction defect, contact lenses should be focused on the retina.
The type of contact lens used depends on the visual impairment and how much the breakage error is. The lens focuses on the diopter (D)
Myopia occurs when the light is in front of the retina as the eyeball is longer than normal. To correct this damage, which is also known as a shortcut, a concave lens is used. This lens is thinner in the center and helps move the focus forward in the retina.
To correct visual impairment, curve of concave contact lenses is determined by the dioptre measurement. The greater the number of diopters, the greater the visual error. In a short-sighted circle, the diopter number is minus (-), indicating that the focus is below the retina.
For hyperopia, the light lies outside the retina. Hyperopia is also known as distant sight as remote objects are clearly visible in this damage. The eyeball is shorter than normal and a convex lens is used to correct visual impairment. The contact lens is thicker in the center and helps to focus the retina
In this case, the curve for the convex contact lenses is determined by the dioptre measurement. The diopter number is preceded by the plus sign (+) indicating that the focus is beyond the retina.
Lenses used for the correction of myopia and hyperopia are considered spherical contact lenses
If the cornea is irregularly shaped, the light on the cornea is focused on more points. The distortion of the image is called astigmatism. Special lenses should be designed, based on individual image distortion. These lenses are known as porous lenses
. Although toric lenses are made of the same materials as rounded lenses, they are designed specifically for individual damage. These lenses have different curvatures, some are thicker and others thinner. These lenses serve to correct astigmatism and myopia or hyperopia.
For presbyopia correction, special bifocal lenses are required, as the person suffering from both requires both short and long-distance correction. Correction of such lenses or near damage is located at the center of the lens, external correction from the outside or vice versa.
The initial lenses were rigid lenses that did not absorb the water. This has prevented the passage of oxygen to the cornea of the eye causing eye irritation and other inconveniences. Then came the soft contact lenses made of hydrogel, which allowed the passage of oxygen through the cornea. These lenses are known as "breathable" contact lenses. This has allowed contact lenses to be worn comfortably and for a long time. Today:
Daily lenses that are removed at night.
Expanded wear-resistant lenses that can be worn for a long time without removal.
Disposable lenses that can be discarded one day, a week or a few weeks
In addition, there are color contacts for cosmetic purposes
- Published On : 3 months ago on March 18, 2018
- Author By : 346@dmin
- Last Updated : March 18, 2018 @ 3:27 pm
- In The Categories Of : Uncategorized