Understanding Contacts

Many people think of contact lenses simply as cosmetic enhancements. But did you know that contact lenses are actually medical devices that correct a variety of conditions? Millions of people require some form of vision correction.1 In Canada 8 in 10 people 18-55 years of age wear eye glasses and 3 in 10 wear contact lenses.2

The type of vision correction you need is one factor that will determine what type of contact lenses your eye care professional will prescribe. Some terms3 you might hear include:

  • Myopia, or near-sightedness: A vision condition in which you can see close objects clearly, but objects further away are blurred.

  • Hyperopia, or far-sightedness: A vision condition in which distant objects are usually seen clearly, but close objects do not come into proper focus.

  • Presbyopia: An age-related vision condition in which there is a gradual loss of the eye's ability to focus on near objects.

  • Astigmatism: A vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye.

  • Coloured contacts: These types of cosmetic lenses are tinted to make your eyes appear a different colour. They can also correct discolorations in your irises.

Remember, only your eye care professional can determine the contact lens and solution combination that is right for you. Everyone has unique eye characteristics, which can affect the types of lenses you're able to wear. See your eye care professional for more information.

  1. Vision Council of America (personal communication, April 2005).
  2. "Contact Lens and Lens Care Market Analysis", Fresh Intelligence, June 2012.
  3. Adapted from the Canadian Association of Optometrists

How Contact Lenses Correct Vision3

Contact lenses are designed to rest on the cornea, the clear outer surface of the eye. They are held in place mainly by adhering to the tear film that covers the front of the eye and, to a lesser extent, by pressure from the eyelids.

As the eyelid blinks, it glides over the surface of the contact lens and causes it to move slightly. This movement allows the tears to provide necessary lubrication to the cornea and helps flush away debris between the cornea and the contact lens.

When in place on the cornea, the contact lens functions as the initial optical element of the eye. The optics of the contact lens combine with the optics of the eye to properly focus light on the retina. The result is clear vision.

  1. Adapted from The Canadian Association of Optometrists

Types of Contact Lenses

These days, lens material technology allows more people to wear contacts than ever before. The latest contact lens innovations include bifocal and multifocal lenses, toric contacts to correct astigmatism, and disposable contacts that are made for daily, weekly or monthly use. In general, though, the two most basic types of contact lenses are soft and rigid gas permeable (RGP):

Soft contact lenses are made of water-absorbing, flexible plastic. They are also referred to as hydrogels. Silicone hydrogels, the latest technology in soft contact lenses, react differently with contact lens solution than traditional hydrogels. OPTI-FREE® PureMoist®, OPTI-FREE® RepleniSH® and OPTI-FREE® EXPRESS® contact lens solutions are designed for use with all types of soft contact lenses including silicone hydrogels.

RGP contact lenses, as the name implies, are made of a more rigid plastic.

Soft contacts are more popular than RGP lenses, as they are typically more comfortable initially on the eye. However, soft lenses are less durable than RGP lenses and must be handled more carefully.

More on Soft Contact Lenses3

Advances in contact lens technologies have created many options in addition to RGP and soft lenses. Today, contact lenses are likely to be described in one of several of the following ways.

By their prescribed wearing period: The time that the lenses are left in the eyes.

Daily Wear: Lenses prescribed for daily wear are to be worn only during waking hours, usually up to a maximum of 18 hours. Daily wear lenses are removed at night and cleaned and disinfected after each removal.

Extended Wear: Extended wear lenses may be worn on an overnight basis for up to seven consecutive days (six nights). You should wear your lenses on an extended wear basis only on the advice of your optometrist.

Extended wear lenses generally have a higher water content or thinner center thickness than other lenses and permit more oxygen to reach the eye. Extended wear lenses need to be cleaned and disinfected at recommended intervals or discarded after use.

By their replacement schedule: The time interval for replacing lenses.

Contact lenses are often prescribed with a specific replacement schedule suitable to your specific needs. At the end of the replacement period, lenses are disposed of and a new lens is used.

  • Single Use (or 'daily disposable' lenses)
    • Wear once for up to 18 hours.
  • Multiple Use: To be worn as long as:
    • 1-2 Weeks
    • 1 Month
    • 1 Quarter

All multiple use lenses require cleaning and disinfection after each period of wear unless they are discarded immediately upon removal.

These replacement schedules are general guidelines. Some patients may need to replace their lenses more often so always refer to your eye care professional’s recommendation.

Why replace lenses frequently?3

Almost immediately after they are inserted, contact lenses begin attracting deposits of proteins and lipids. Accumulated deposits, even with routine lens care, begin to erode the performance of your contacts and create a situation that presents a greater risk to your eye health.

A specific replacement schedule helps to prevent problems before they might occur. Contact lens wearers, in turn, enjoy the added comfort, convenience and health benefits of a planned replacement program.

  1. Adapted from The Canadian Association of Optometrists

Remember, only your eye care professional can determine the contact lens and solution combination that is right for you. Everyone has unique eye characteristics, which can affect the types of lenses you're able to wear. See your eye care professional for more information.

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