The Science Behind Using Contact Lenses for Vision Impairment

Representative Image - The human retina, a CRISPR therapy has been inserted directly into a person for the first time — in the eye.Prof. P. Motta/Dept. of Anatomy/University La Sapienza of Rome/SPL

Contact lenses are used for vision reconstruction and are placed on the eye cornea. They do the same corrective function that traditional spectacles, or glasses, do. However, comparatively, they are incredibly light in weight and are undetectable for all purposes. Contact lenses can assist in forming the image on the eye’s retina by either diversion or converging the rays of light entering the eye.

How Contact Lenses evolved?

Earlier contact lenses were composed of glass and were scleral lenses. Scleral lenses are extended contact lenses that cover the entire sclera – the eye’s white outer coating. These primitive lenses could only be worn for a short period. With the development of polymethyl methacrylate (PPMA) – in the 1930s, plastics were first applied in contact lenses. These were hybrid, scleral lenses, made with both plastic and glass, in 1936.

By the 1940s, much smaller contact lenses were produced that covered only the eye’s cornea and not the whole eye.

Types of Vision Impairments

One of the practical uses of contact lenses is to improve visual defects. The general impairments are Hyperopia, Myopia, Presbyopia, and Astigmatism.

  • Hyperopia – It is also called as Hypermetropia, and the image of the object is set behind the retina. Distant objects can be seen properly, and the near objects seem to be blurred. Hyperopia is more also known as farsightedness, and more than 16 percent of the kids in the United States between the age of 5 to 15, suffer from it. The use of convex contact lenses can improve the defect.
  • Myopia – is an eye disability where the image of the object seen is set in front of the retina. During this impairment, one can see near, not the distant objects, which appear blurred. This defect is also known as nearsightedness. This is a pervasive impairment, with over 29 percent of the adults in the United States suffering from it. The use of concave contact lenses can correct the defect.
  • Presbyopia – This is an impairment that comes with age, usually after the age of 45. The impairment grows as the lens of the eye loses its flexibility. Bifocal contact lenses are utilized to correct this vision defect.
  • Astigmatism – This happens when the eye’s lens has more than one focal point, in different meridians. Astigmatic people cannot see in minute details and need cylindrical lenses to solve their impairment. Nearly 30 percent of American children in the age group 5 to 16 have this impairment.

Lenses Used For Vision Correction

In normal vision, the light from the object hits the cornea and converges on the retina. Due to any refractive error, at times, the light from the item does not focus on the retina, but either behind it or in front of it. To fix this error, contact lenses are used to focus on the retina.

The kind of contact lenses applied depends on vision impairment and how much refractive error is concerned. The capacity of the lens bending the light to converge on the retina is measured in diopters (D).

Myopia occurs when the light is directed in front of the retina, as the eyeball is longer than usual. To solve this impairment, which is also known as nearsightedness, a concave lens is applied. This lens is thinner in the middle and helps change the focus ahead, near the retina.

The curve in the concave contact lenses is managed by the diopters’ measurement to correct this vision impairment. The larger the number of diopters, the larger is the vision defect. In myopia, the diopter number is represented by a minus (-) sign, showing that the focus is short of the retina.

In the case of hyperopia, the light is centered beyond the retina. Hyperopia is also known as farsightedness, as far away objects are seen clearly in this impairment. The eyeball is smaller than usual, and a convex lens is used to solve this vision defect. The contact lens used is thicker in the middle and helps shift the focus back onto the retina.

In this case, too, the curvature needed in the convex contact lenses is defined by the measurement in diopters. The diopter number is symbolized by the plus (+) sign, indicating that the focus is beyond the retina.

The lenses applied for the correction of myopia and hyperopia are classified as spherical contact lenses.

When the cornea is unevenly shaped, the light from the object falling on the cornea directs more than one point. This falsification of the image is called astigmatism. Special lenses need to be created based on the individual’s distortion of the picture. These lenses are recognized as toric lenses.

Though toric lenses are composed of the same materials as the spherical lenses, they are specially designed to suit individual impairments. These lenses have different curves, thicker in some places, and thinner in others. These lenses are designed to correct myopia and astigmatism or hyperopia if needed.

For the correction of presbyopia, particular bifocal lenses are needed, as the person experiencing it requires both modifications for farsightedness and nearsightedness. In such lenses, either the repair for near impairment is placed in the center of the lens, with the remote correction on the outside, or vice versa.

Types Of Contact Lenses

The initial lenses were hard lenses that could not absorb water properly. This stopped the oxygen from passing into the eye’s cornea, irritating the eyes. 

Then arrived soft contact lenses made from hydrogel, which let oxygen pass through them to the cornea. These lenses came to be recognized and marketed as ‘breathable’ contact lenses. This made it feasible for contact lenses to be worn without discomfort and for more extended periods. 

Today, there are:

  • Daily wear lenses, which are removed every night. 
  • Extended wear lenses can be used for extended periods without removing it.
  • Disposable lenses can be disposed of after a few days, a week, or a few weeks.
  • Also, there are color contacts, which are for cosmetic purposes.

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