How contact lenses work
Contact lenses work by sitting directly on the tear film that covers the surface of your eye, correcting vision in a way similar to glasses, but without the frames or bulk. Here’s how they function:
1. Vision Correction
Contact lenses are made from thin, transparent materials that help focus light correctly onto the retina, the light-sensitive tissue at the back of the eye. When your eyes are unable to focus light properly (due to conditions like nearsightedness, farsightedness, or astigmatism), contact lenses reshape the path of incoming light to ensure that it focuses sharply on the retina, giving you clear vision.
2. Types of Vision Problems Contacts Correct
Nearsightedness (Myopia): The eye focuses light in front of the retina. Contact lenses help redirect light to focus on the retina.
Farsightedness (Hyperopia): The eye focuses light behind the retina. Contact lenses bend light so it focuses properly on the retina.
Astigmatism: Irregularly shaped corneas distort light entering the eye. Special toric lenses adjust light in specific directions to correct the distortion.
Presbyopia: As people age, they may need multifocal or bifocal contact lenses, which allow both near and distant objects to be seen clearly.
3. How Contacts Stay in Place
Contact lenses are designed to float on the tear film on the surface of the cornea. The natural curve of the eye and the surface tension of the tear layer hold the lenses in place. The lenses are shaped to fit the curvature of the eye, which allows them to stay centered over the cornea and move with your eye when you look in different directions.
4. Types of Contact Lenses
Soft Contact Lenses: Made of flexible, water-absorbing materials that allow oxygen to pass through to the cornea, they are comfortable and used for most common vision corrections.
Rigid Gas Permeable (RGP) Lenses: These lenses are made of a firmer material, providing sharper vision in some cases (especially for people with astigmatism or irregular corneas). They are also breathable, allowing oxygen to reach the cornea.
Toric Lenses: These are special lenses designed for people with astigmatism. Their shape is slightly different to account for irregular corneas and prevent rotation on the eye, ensuring consistent vision.
Multifocal/Bifocal Lenses: Designed for people with presbyopia, these lenses have multiple power zones, allowing clear vision at different distances.
5. How Contact Lenses Let Oxygen Through
The cornea doesn’t have its own blood supply, so it gets oxygen from the air. Contact lenses are designed to be oxygen-permeable, meaning they allow oxygen to pass through to the cornea. This is crucial for keeping your eyes healthy, as reduced oxygen can lead to complications like dryness, irritation, or corneal damage.
6. Daily vs. Extended Wear Lenses
Daily Wear Lenses: These are worn during the day and removed at night to clean and disinfect them.
Extended Wear Lenses: Made from materials that allow more oxygen to reach the eye, these lenses can be worn continuously, including overnight, for a set period (typically up to 7 days or longer).
7. Tear Film and Lubrication
Contact lenses rely on the natural tear film on the eye to stay hydrated and comfortable. Your tears help keep the lens moist, reduce friction, and prevent discomfort. If your eyes don’t produce enough tears (or if they dry out), you may experience discomfort, which can be mitigated with artificial tear drops or specially designed lenses for dry eyes.
8. UV Protection
Some contact lenses come with built-in UV protection, helping shield your eyes from harmful ultraviolet rays. However, contacts only cover part of your eye, so wearing sunglasses with UV protection is still recommended for full protection.
9. Proper Care and Hygiene
Contact lenses require regular cleaning, disinfecting, and storing in a special solution to avoid infections, irritations, or other complications. Improper handling of contact lenses can lead to bacterial infections, corneal ulcers, or damage to the eye’s surface.
In summary, contact lenses work by reshaping light as it enters the eye, allowing it to focus properly on the retina for clear vision. They stay in place with the help of the eye’s natural tear film, and their material allows oxygen to reach the cornea, ensuring eye health. Proper care is essential to keep both the lenses and your eyes healthy!
References
(2015). Switzerland : FDA approves Roche's Lucentis (ranibizumab injection) for treatment of diabetic retinopathy in people with diabetic macular edema. MENA Report, (), n/a.
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