People choose to wear contact lenses for many reasons. Aesthetics and cosmetics are the main motivating factors for those who want to avoid wearing glasses or to change the appearance of their eyes. Others wear contact lenses for functional or optical reasons. When compared with spectacles, contact lenses typically provide better peripheral vision. This can make them preferable for sports and other outdoor activities. Contact lens wearers can also wear sunglasses, goggles, or other eyewear of their choice without having to fit them with prescription lenses or worry about compatibility with glasses.

Some conditions such as keratoconus and aniseikonia are typically corrected better with contact lenses than with glasses.

The average age of contact lens wearers globally is 31 years old, and two-thirds of wearers are female.

Corrective spherical contact lenses are designed to improve vision, most commonly by correcting refractive error. This is done by directly focusing light so it enters the eye with the proper power for clear vision.

A spherical contact lens bends light evenly in every direction (equally horizontally and vertically). They are typically used to correct myopia, (short sightedness) and hypermetropia (far sightedness).

Monovision is the use of single-vision lenses (one focal point per lens) to focus an eye (typically the dominant one) for distance vision and the other for near work. The brain then learns to use this setup to see clearly at all distances.

A cosmetic contact lens is designed to change the appearance of the eye. These lenses may also correct refractive error. Although many brands of contact lenses are lightly tinted to make them easier to handle, cosmetic lenses worn to change eye color are far less common, accounting for only 3% of contact lens fits.

Due to their medical nature, coloured contact lenses, similar to regular ones, are illegal to purchase without a valid prescription. Those with perfect vision can buy colour contacts for cosmetic reasons, but they still need their eyes to be measured for a "zero" prescription. This is for safety reasons, so the lenses will fit the eye without causing irritation or redness.

While asleep, oxygen is supplied from the blood vessels in the back of the eyelid. A lens in the eye while asleep, can hinder the passage of oxygen to the cornea causing oxygen starvation to the cornea which can result in serious complications, such as corneal ulcer that, if left untreated, can permanently decrease vision

Wearing lenses designed for daily wear overnight also has an increased incidence of corneal neovascularization (small vessels growing int the clear cornea). This condition, once it sets in, cannot be reversed and will eventually spoil vision acuity through diminishing corneal transparency.

Before touching the contact lens or the eye, it is important to wash hands thoroughly with soap and rinse well. Drying of hands using towels or tissues before handling contact lenses can transfer lint (fluff) to the hands and, subsequently, to the lenses, causing irritation upon insertion. Towels, unless freshly laundered on high temperature wash, are frequently contaminated with large quantities of bacteria and, as such, should be avoided when handling lenses.

Dust, lint and other debris may collect on the outside of contact lenses. Again, hand contact with this material, before handling contact lenses, may transfer it to the lenses themselves. Rinsing the case under a source of clean running water, before opening it, can help alleviate this problem. Next the lens should be removed from its case and inspected for defects (e.g. splits, folds, lint). A 'gritty' or rough appearance to the lens surface may indicate that a considerable quantity of proteins, lipids and debris has built up on it and that additional cleaning is required; this is often accompanied and felt by unusually high irritation upon insertion.

The technique for removing or inserting a contact lens varies depending upon whether the lens is soft or rigid. There are many subtle variations to insertion and removal techniques. Because of differences in anatomy, manual dexterity, and visual limitations, every person must find the technique that works best for them. In all cases, the insertion and removal of lenses requires some training and practice on part of the user. If in doubt, please contact your eye care practitioner.

Lens care varies depending on material and wear schedule. Daily disposables are discarded after a single use and thus require no cleaning. Other lenses need regular cleaning and disinfecting to prevent surface coating and infections. There are many ways to clean and care for your lenses.

Multipurpose solutions:

This is the most common method for rinsing, disinfecting, cleaning, and storing soft lenses. The latest multipurpose solutions also contain ingredients that improve the surface wetability and comfort of silicone hydrogel lenses.

Hydrogen peroxide systems:

Hydrogen peroxide can be used to disinfect contact lenses. Care should be taken not to get hydrogen peroxide in the eye because it is very painful and irritating. The instructions need to be followed as directed. Hydrogen Peroxide solution should never be put directly into the eye.

Daily cleaner:

Used to clean lenses on a daily basis. A few drops of cleaner are applied to the lens while it rests in the palm of the hand; the lens is rubbed for about 20 seconds with a clean fingertip (depending on the product) on each side. Lens must then be rinsed with daily cleaner. Aside from cleaning the contact lenses, it is highly advised to also clean the cases to avoid any possible infection. Replacing the case monthly and storing it in a clean and safe environment is also recommended.

Researchers have linked ultraviolet (UV) light to the formation of cataracts. Exposure to excessive UV light also may result in a condition called photokeratitis, that's why some contact lenses now contain a UV-blocking agent. You can't tell if a contact lens has a UV blocker just by looking at it. The blocking agent is clear, so as not to disturb vision. The contact lens packaging will specify if the product has a UV blocker, or you can ask your eye care practitioner.

Very important: UV-blocking contacts are not meant to replace sunglasses. A contact lens covers only your cornea, not your entire eye.

However, UV-blocking contact lenses do help protect the portion of the white of your eye that is covered from formation of growths such as pingueculae and pterygia.

Sunglasses with UV protection can cover more of your eye and the parts of your face that surround the eye, depending on the size of the sunglass lens. That's why contacts with UV blockers are designed to complement sunglass use as an added protection.

Contact lenses are generally safe as long as they are used correctly. Complications from contact lens wear affects roughly 5% of wearers yearly. Factors leading to eye damage varies, and improper use of a contact lens may affect the eyelid, the conjunctiva, and, most of all, the whole structure of the cornea. Poor lens care can lead to infections by various microorganisms

Many complications arise when contact lenses are worn not as prescribed (improper wear schedule or lens replacement). Sleeping in lenses not designed or approved for extended wear is a common cause of complications. Many people go too long before replacing their contacts, wearing lenses designed for 1, 14, or 30 days of wear for multiple months or years. While this does save on the cost of lenses, it risks permanent damage to the eye and even loss of sight.

Mishandling of contact lenses can also cause problems. Corneal abrasions can increase the chances of infection. When combined with improper cleaning and disinfection of the lens, a risk of infection further increases. Decreased corneal sensitivity after extended contact lens wear may cause a patient to miss some of the earliest symptoms of such complications.

Safety Tips:

1. DO always rub contact lenses when you clean them, even if using a "no-rub" solution.
2. DO make sure contact lenses and lens storage cases are cleaned and disinfected regularly.
3. DO replace contact lenses regularly, according to your Eye Care Practitioner's directions.
4. DO put your lenses in before applying Eye Makeup.
5. DO always wash hands before handling contact lenses.
6. DO remove lenses before removing Eye Makeup.
7. DO have an annual checkup to ensure your eyes remain healthy and to check lens powers.
8. DON'T place contact lenses in your mouth or use your saliva to wet them.
9. DON'T "top off" old solution in your contact lens case. Instead, discard old solution and replace it with fresh solution.
10. DON’T apply eyeliner between your lashes and your eye.