Contact Lenses

Types of Contact Lenses, Full Eye and Otherwise

In the 16th century, the idea of contact lenses first came out. Leonardo da Vinci suggested a method of submerging the head in a water bowl or wearing a glass hemisphere filled with water over the eyes for exploring accommodation mechanisms rather than vision correction.

Later on, Descartes suggested a liquid-filled glass tube capped with a lens for vision correction. But this was not implementable as it would make blinking impossible for being in direct contact with the cornea.

Thomas Young used Descartes’ model in the 19th century. He corrected the refractive power by using another pair of lenses. The water-filled lenses were affixed by using wax.

Sir John Herschel, in 1845, suggested two ideas for the correction of vision: an animal jelly-filled glass capsule which will be spherical, and a cornea mold impressed on a transparent medium. He never tested his ideas. But these ideas were used to refine the making of molds and perfecting the shape of lenses according to eye shape by Joseph Dallos, a Hungarian physician.

Louis J. Girard, in 1887, invented a scleral contact lens or a full eye lens. Still, the first a focal scleral contact lens was fabricated in 1888, by a German ophthalmologist Adolf Gaston Eugen Fick. The lenses were made with blown glass, approximately 18-21mm in diameter, rested on the tissue surrounding the cornea. These tissues are less sensitive, but the lenses could only be worn for a few hours. The same year, August Muller from Germany, manufactured a more suitable blown glass scleral lens which cured his own myopia.

With the 20th century came the development of PMMA, polymethyl methacrylate, and opened the way for plastic scleral lens manufacture. A hybrid lens made from plastic and glass was introduced in 1936 by William Feinbloom. A complete plastic lens was produced in 1939 by Dr. Istvan Gyorffy.

Rigid and Cornea Lenses (1949-1960s)

In 1949, the corneal lens was made. These were smaller and sat on the cornea rather than all the visible ocular surface or full eye. These lenses could be worn for longer hours. 

During the 1960s, the lens became more viable and soft.

Soft and Gas Permeable Lenses (1959-current)

PMMA lenses don’t allow oxygen to pass the cornea and conjunctiva. This could cause potentially severe and adverse clinical effects. This problem was addressed by the development of oxygen-permeable but rigid materials during the 1980s and 1990s. Norman Gaylord is a prominent name when it comes to the development of oxygen permeable lenses.

In soft lenses, the major breakthrough was made by Otto Wichterle and Drahoslav Lim, Czech chemists, in 1959. The work of these scientists led to the production of hydrogel lenses in various countries in the 1960s. In 1971, Food and drug administration, the USA approved the Softens material. This material offered much greater comfort. The polymers improved over the next 25 years. Rishi Agarwal, a British Optometrist in 1972, suggested disposable soft contact lenses for the first time.

Another milestone was the introduction of silicone hydrogel contact lenses in 1998. They were highly porous and could be worn for an extended period. Later on, the second-generation silicone hydrogel was introduced galyfilcon A and senofilcon A. Right now, for contact lenses, third-generation polymer Comfilcon A is used for its very high oxygen permeability.

Types of Contact Lenses

Contact lenses can be classified:

  • By their function.
  • Material used.
  • How long they can be worn.
  • Replacement plan.

Soft Contact Lenses

These lenses are made from flexible, soft plastics, silicone hydrogel, which is oxygen permeable. These are very easy to adjust to and comfortable to wear.

Rigid Gas Permeable Contact Lenses

 These lenses are durable, provides a crisper and clearer vision, and are resistant to deposition. They are cheaper and easy to handle. But they are a bit more challenging to get used to. They might take a week or two for adjustment as compared to a few days for soft lenses.

Extended Wear Contact Lenses

These contact lenses are worn for longer durations, overnight or six nights, or maybe up to 30 days. These are soft contact lenses made up of oxygen permeable material. Some rigid gas permeable lenses are also approved extended wear lenses. After every scheduled removal, it’s good that the eyes get at least a night rest without lenses.

Disposable Contact Lenses

By the definition of FDA, disposable means use once and then discard. According to lens sellers, soft contact lenses are called disposable, following a replacement plan. The extended wear lenses may be worn for the prescribed period and then discarded.

Scleral Lens

Also known as Sclera Contact Lens or full eye lens. These are large lens that rests on the sclera or white part of the eye. These lenses are designed to cure many eye conditions, out of which some are non-responsive to other treatments.

Medical Uses

These lenses are used to improve light sensitivity, vision and reduce pain caused due to various disorders or eye injuries. Eyes disorders that can be treated using scleral lenses are microphthalmia, dry eye syndrome, Stevens-Johnson syndrome, corneal ectasia, keratoconus, and aniridia neurotrophic keratitis, Sjogren’s syndrome, high order eye aberrations, post LASIK complications, post corneal transplant complications, and pellucid degeneration. Chemical and burn a scleral lens can also treat injuries, surgical complications, and distorted corneal implants.

Special-Effect Scleral Contact Lenses

Sclera lenses are also referred to as special-effect lenses. They dramatically change the wearer’s eyes appearance. These lenses, used for costume purpose, have no fluid reservoir and are soft with a little resemblance with scleral gas permeable contact lenses. These are not designed for vision correction. These lenses are used in Hollywood movies like Underworld, the blacked-out eyes, and Underworld: Evolution, Star Trek, and Evil Dead, the whited-out eyes. These lenses are uncomfortable and can impede the wearer’s vision. However, they produce striking visual effects. These lenses could be the star of the costumes in Halloween. These can be customized as well. Imagine the number of ways these lenses can be used.

In cognitive science or ophthalmology, these full eye lenses are embedded with magnetic field sensors that are useful to measure eye movements. 

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