A contact lens is an artificial lens that sits on the surface on the eye. It covers the iris and pupil but may also extend to the white part of the eye (sclera). Contacts are commonly prescribed for vision correction in those who don’t want to wear eye glasses or undergo refractive surgery. Compared to glasses, they offer a wide field of view. They also don’t mist up with temperature changes.
Contact lenses are available as single-vision or multifocals. Single-vision lenses contain only a single point of focus throughout the lens. They can be used to achieve blended vision (monovision) by placing a far-powered lens on the dominant eye and a near-powered lens on the other eye. Multifocals offer more than one lens power. They correct more than a single vision problem.
Contacts can be categorized depending on the material as follows:
- Soft lenses – These are lenses made from a gel-like plastic known as hydrogel. They are soft and easily conform to the surface of the eye. Newer soft lenses are made from silicone hydrogel. These are more porous, allowing oxygen to get to the cornea. Although comfortable, most soft lenses are disposed after a short period of wear.
- Gas permeable (GP) lenses – These are termed as rigid gas permeable lenses. They are a type of hard lenses which provide excellent optics. They are also porous and fit well. The downside to the lenses is that they are not very comfortable. Wearers often take some time to adapt.
- Hybrid contact lenses – They combine the strengths of the soft and the GP lenses. Hybrid contacts have a central region that provides sharp vision and an outer region made from silicone hydrogel for comfort. Their disadvantage is that they are hard to fit.
- PMMA lenses – The lenses are made from a rigid material known as polymethyl methacrylate. They fit well and provide crisp-clear optics. However, they do not allow passage of oxygen and are also difficult to adapt to.
Contacts can be used for various purposes which include:
- Vision correction in refractive errors – The right lenses can correct presbyopia, hyperopia, myopia and astigmatism. In case of two disorders such as presbyopia and farsightedness, multifocals lenses can be used.
- Treatment of keratoconus and other corneal irregularities – Scleral lenses are used in management of keratoconus where the cornea is cone-shaped instead of curved. The smooth shape of the lens covers up for other corneal irregularities such as in astigmatism.
- Protection from UV light - Rays from the sun can be damaging and may even cause cataracts. UV-inhibiting lights protect the eyes from the effects of radiation.
- Masking a disfigured eye – Contact lenses can also be used to mask a disfigured eye, to make it look similar to the other eye.
- Correcting unevenness in color – In people with albinism or coloboma, the eye color may be pale. Tinted/colored lenses can be used to correct this.
Problems Associated with Contact Lens Wear
Contacts can be a source of eye problems when they don’t fit well, are damaged, or are not well cared for. The problems may include:
- Corneal infections such as keratitis and conjunctivitis
- Allergic reactions
- Dry eyes
- Contact-lens induced red eye
- Poor vision
Caring for Contact Lenses
Contacts can be worn for a single day only or continuously depending on the type of lenses. Those disposed after a single day's wear are termed as daily disposable lenses. Other lenses can be worn continuously for weeks or months. Extended wear lenses made of reusable material can be worn daily for even up to six months or longer.
Apart from the dust and particles from the environment, protein deposits from the eye contaminate lenses. Those worn continuously should be cleaned, disinfected and stored properly to prevent infections to the eyes. The products available include:
- Daily cleaner solutions – These are used for cleaning the lenses.
- Saline lens solutions – Contacts are rinsed as well as stored in saline solutions
- Multipurpose solutions – They come as an all-in-one product. Multipurpose solution clean, disinfect, rinse, and are used to store contact lenses. However, they contain preservatives which could cause reactions to people who are allergic.
- Hydrogen peroxide – It is also a multipurpose solution but without a preservative. Neutralizers should also be used before placing contacts on the eyes. Without neutralization, the chemical can cause injury to the eyes.
- Protein deposit and enzyme cleaner – This type cleans the accumulated protein and enzyme build-up from the lenses.
- Eye drops – Some drops are formulated for lubrication of contacts, preventing dry eyes.
- Cleaning/disinfecting devices – Equipment with ultrasonic waves can also be used for contact lens care.