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THE TECHNOLOGY OF CONTACT LENSES AND THEIR FUNCTIONS

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Are you new to the world of contact lenses and don't really know a thing about it? If yes, then you landed in the right place. Here's your guide to contact lenses technology and how it functions.

Contact lenses are ocular prosthetic devices used to correct refractive errors primarily used by individuals who don’t prefer wearing glasses or undergoing LASIK surgery.

Cosmetic contact lenses may be used to change the eyes' appearance, for example, the use of black contact lenses as a part of costumes in Halloween.

Contact lenses are thin and curved in appearance and are placed in ‘contact’ with the eye.

Types of Contact Lenses and their technology

  • Soft Lenses

Soft lenses are made up of hydrogel, which is water containing, gel-like plastic. Because of its high-water content, they let in more oxygen into the cornea.

They provide comfort and excellent clinical performance because they are thin, pliable, and can easily be rolled around without damaging the lens.

  • Silicone Hydrogel Lenses

Silicone hydrogel lenses are one step ahead in the technology of the soft lens. They are more porous, resulting in a higher permeability of oxygen due to the presence of silicone. 

Because of this, many daily-wear prescribed contact lenses are silicone hydrogel lenses.

Despite being recommended for daily wear, there are two significant setbacks of silicone hydrogel lenses:

  1. Rigidity
  2. Hydrophobic nature of lens surface

Any of the following three methods may be used to overcome this:

  • Plasma coating
  • Longer backbone polymer chains
  • Internal rewetting agents   

Colored lenses, like black contact lenses, are also manufactured by this technology.

  • Rigid Lenses

More commonly known as ‘hard’ lenses or PMMA lenses, rigid lenses are made up of a transparent, rigid plastic called polymethyl methacrylate.

They were unpopular because of the lack of comfort and lack of oxygen reaching the cornea. This also led to serious clinical complications.

  • Gas Permeable Lenses

Gas permeable lenses are similar in appearance and texture to rigid lenses. However, they are permeable to oxygen, as the name suggests itself. 

Although it takes more time for an individual to adapt to a GP lens, it provides a sharper vision than a soft lens and silicone hydrogel lens, especially for patients with astigmatism. 

  • Hybrid Lenses

Hybrid lenses are designed to offer the clarity of a gas permeable lens and the comfort and adaptability of a soft lenssilicone hydrogel lens. They have a center made up of a rigid gas permeable lens surrounded by hydrogel or silicone hydrogel ‘skirt’.

Because of how costly and difficult it is to fit these lenses; they are not used by the majority of people. 

Manufacturing Technology

While rigid lenses are mostly custom made, soft lenses undergo mass production. Following are few of the methods of soft lens manufacturing:

1). Spin-cast lenses

These are produced by rotating liquid silicone in a mold at high speed. Although this method is cost-efficient, a significant drawback is that the shape is not entirely spherical.

2). Molded lenses

This method is close to sin casting; however, the use of computer controls and injection molding ensures a perfect shape. Throughout the rotational process, the lens is kept hydrated.

3). Diamond Turning

The machine that does single point diamond cutting is called the CNC lathe. The diamond acts as the cutting tool, which is carved according to the lens's geometry. This method ensures ultra-precision and accuracy.

This method may be used for both soft and hard lenses.

Functions of Contact Lenses

1). Refractive Error Correction

Vision problems occur when the light is unable to refract correctly and either focuses on the retina's front or back

A contact lens bends light equally in all directions to eradicate medical issues like myopia (short-sightedness) and hypermetropia (farsightedness) by focusing light directly on the retina.

To resolve complications like that of astigmatism (the uneven focus of light on the retina), a toric contact lens is used, which focuses light differently horizontally and vertically.

2). Correction of presbyopia

The weakness of the eye caused by aging is quite common. Usually, reading glasses are prescribed to individuals with presbyopia, but contact lenses can also be worn.

3).Colour correction

A red-tinted contact lens sometimes helps color blind people in differentiating colors. It can also be used in some cases of light sensitivities.

4). Cosmetic Contact Lenses

Cosmetic contact lenses are used to change the appearance of the eye. They may also correct the refractive error, but they are principally used to enhance or change eye color, for example, black contact lenses.

Black contact lenses of the type ‘circle contact lenses’ are trendy in China and Japan as they give an impression of a bigger iris and hence, doll-like eyes.

Cosmetic contact lenses are also famous for their use in the production design for TV shows and films. Lon Chaney was the first actor to wear contact lenses on-screen in his movie ‘The Road to Mandalay’ in 1926.

The use of black contact lenses in films and movies is significantly higher than other colors because of their use to depict supernatural creatures like vampires. Black contact lenses can also be used to enhance prosthetics used in movies to frighten you. Black contact lenses are also very popular in the Halloween season when people use them as part of their costumes.

As cosmetic contact lenses are medical, they have clinical applications as well. They are sometimes used to restore appearance and functionality in eyes with a damaged or no iris.

5). Therapeutic Scleral Lenses 

This lens covers the sclera as well as the cornea, as the name suggests. Patients with abnormally sensitive cornea are usually prescribed scleral lenses to reduce pain and light sensitivity. These lenses are also prescribed when there are post-LASIK complications, chemical or burn injuries, surgical injuries, and to treat multiple disorders like severe dry eye syndrome.

6). Therapeutic Soft Lenses

Therapeutic Soft lenses are used mostly in cases when the cornea requires time to heal. They protect the cornea from external particles and the continuous rubbing of the eyes.

Soft lenses that can supply medicinal drugs directly to the eye have also been developed.

Final Word

Getting your first pair of contact lenses can be exciting. But it is always wise to do your research beforehand and know the ABC of lenses. This will save you from wronging both your eyes and lenses. We hope this article serves to educate all the new wearers and those who are planning to get the contact lenses. Let us know your views in the comments below. 

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