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Contact lenses are considered medical devices, which have been regulated by the U.S. Food and Drug Administration (FDA).
Most people choose contact lenses over glasses because they have many advantages - they can adjust the amount of light entering your eyes for optimum vision, they sit directly in your eyes, so peripheral vision isn't obstructed, there is no fear of breakage, and so on.
However, contact lenses have their own share of side effects too, which we are going to write about in this article.
Side Effects Of Contact Lenses
1. Dry eyes
Most contact lenses wearers suffer from dry eye problems. Wearing contact lenses reduces the quantity of tears and decreases oxygen levels to the cornea. This leads to itchiness or stinging pain, and irritation on the eyelid or the cornea and its surrounding tissues  .
2. Corneal abrasion
Corneal abrasion occurs when the contact lenses scratch your cornea, if they aren't fitted properly or when your eyes are too dry. Also, sleeping with contact lenses increases the risk of corneal abrasion. The lenses trap dirt and bacteria and it gets rubbed against the cornea, which can lead to eye infections  .
3. Obstructs oxygen flow to the eyes
The cornea does not have blood vessels, apart from its edges. Without sufficient oxygen, the cornea's metabolism is stressed and lactic acid builds up creating an osmotic load, drawing water into the cornea faster than it can be removed, resulting in corneal swelling or oedema  .
The amount of oxygen available under a lens varies with lens material and thickness.
4. Corneal ulcer
Another side effect of contact lenses is corneal ulcer, which occurs when bacterial contamination develops on the surface deposits on soft contact lenses and can multiply fast there. This creates a bacterial biofilm supplying infectious agents to a stressed cornea  .
5. Red eye
Red eye occurs when you wear contact lenses for longer hours, especially throughout the night. This provides a moist and humid environment for the micro-organisms to breed. Other causes of the red eye include deformed lenses, lens deposits that lead to irritation, or poorly fitting lenses  .
6. Superficial keratitis
Superficial keratitis is the irritation of the outermost layer of the cornea, which causes due to lens care solutions, allergies, infection, and mechanical irritation  .
7. Corneal molding
Molding is the changes in the shape of the cornea due to wearing of contact lens. It mostly occurs due to oxygen deprivation and the formation of bubbles under contact lenses at reduced pressures, as experienced during flight at high altitudes  .
Infiltrates appear as hazy, grey areas in the mid-region of the cornea which occur due to wearing contact lenses for longer periods, poor contact lenses fitting, wearing different types of lenses, and poor lens care regime  .
9. Giant papillary conjunctivitis
Giant papillary conjunctivitis is a complication that arises among soft contact lenses wearers, especially those who wear them for extended periods. The symptoms are increased mucous production and mild blurred vision  .
-  Contact Lens Use Under Adverse Conditions: Applications in Military Aviation. National Research Council (US) Working Group on Contact Lens Use Under Adverse Conditions.Washington (DC):National Academies Press (US); 1990.