What are Contact Lenses?

Contact lens (singular) is a thin film made of plastic which fits on the cornea to correct vision or for cosmetic purposes. Less commonly used these days are contact lenses made of glass.

In a person with vision problems, the light refraction (bending of light) is not adequate to allow for a clear image to be projected onto the retina. In a person who is short-sighted (myopia), distant images are blurred, while in a person with far-sightedness (hyperopia), distant objects are clear but near objects are blurred. Contact lenses can correct this by adding another medium on top of the cornea to refract light to the degree that is lacking for proper vision.

Modern technology has now allowed for contact lenses to be developed for patients with astigmatism (toric contact lenses) and age-related changes known as presbyopia, where vision is corrected with bifocal contact lenses.

Types of Contact Lenses

The two main types of contact lenses are the flexible soft contact lenses and the more rigid hard contact lenses.

Soft lenses are made of a plastic polymer and while they are prone to tearing, they are less likely to cause an infection of the eye. Soft lenses are available as disposable lenses where a new set of lenses are used on a daily or monthly basis. Used pairs can be discarded and the low cost of soft lenses makes it both an affordable and safe option.

The hard contact lens, also known as rigid gas permeable lenses, are made of a silicone hydrogel and provide a better degree of correction for vision problems than soft lenses. Hard lenses are more durable than soft lenses and are necessary for presbyopia and some cases of astigmatism. Hard lenses can also be used for myopia and hyperopia as well but there is a move towards daily wear soft lenses for these conditions.

There is still much concern about contact lenses allowing for oxygen circulation around the eye. Both the soft lens and hard lens is now developed with materials that allow for oxygen permeability meaning that oxygen can reach the cornea. However, if these lenses are used continuously for days and while sleeping, oxygen circulation may be hampered.

Contact lens are usually clear in color or may have a slightly blue tinge which will not affect the eye color but make it more visible in the contact lens solution in which it is stored. Corrective lenses can be tinted in order to change the eye color (iris) while still correcting vision problems. These days cosmetic lenses are available which has no therapeutic benefit but can change the eye color as one wishes.