CONTACT LENSES
Contact lenses are an excellent choice for those who needs vision correction and want to avoid wearing spectacles or undergo LASIK surgery.
Contact Lens Material
There are five types of contact lenses, based on type of lens material they are made of:
Percentage of contact lens materials
Soft lenses are made from hydrogels which is a gel-like, water-containing plastics. Being very thin and pliable they conform to the front surface i.e CORNEA. Introduced in the early 1970s, these made contact lenses more popular as were very comfortable.
- The only alternative at that time was hard contact lenses (PMMA plastic material) whichtook weeks to get adapted to.
Silicone hydrogel lenses are advanced soft contact lenses.
These are more porous than regular hydrogel lenses and hence allow much more oxygen to reach the cornea. Introduced in early 2000’s, these are now the most popular lenses prescribed in the United States.
Gas permeable lenses (GP or RGP lenses)— these are rigid contact & are porous which allows oxygen to pass through them. Because they are oxygen permeable, GP lenses can be fit closer to the eye than PMMA lenses& this makes them more comfortable than conventional hard lenses. GP contacts provide sharper vision than soft and silicone hydrogel contacts especially incases of astigmatism.
It usually takes some time for your eyes to adjust to RGP lenses but after this initial phase, most people find GP lenses are as comfortable as hydrogel lenses.
Hybrid contact lenses have advantage ofcomfort like soft/silicone hydrogel lenses, combined with the crystal-clear optics of GP lenses. These have a rigid gas permeable central zone surrounded by a outer “skirt” of hydrogel /silicone hydrogel material.
These are more difficult to fit and are more expensive to replace than soft lenses.
PMMA lenses are made from a transparent rigid plastic material called polymethyl methacrylate (PMMA). PMMA lenses have excellent optics, but don’t allowoxygen transmission and can be difficult to adapt to. These have virtually been replaced by GP lenses and are rarely prescribed today.
In 2017, more than 2/3rd contact lenses prescribed in the U.S.A were silicone hydrogel lenses, followed by soft (hydrogel) lenses (1/5 th), gas permeable lenses (11 percent).
Contact Lens Wearing Time
- Daily wearlenses — must be removed nightly.
- Extended wearlenses— can be worn overnight, usually for seven days consecutively without removal.
-
- “Continuous wear”lenses – used to describe lens wear for 30 consecutive nights (which is the maximum wearing time approved by the FDA for certain brands of extended wear lenses).
Replacing the LensesContact lenses should be replaced frequently to prevent the build-up of lens deposits and more importantly contamination which increases the risk of infections. These may be:
-
-
- Daily disposable — Discarded after 1 day of wear.
- Disposable lenses — Discarded every 2 weeks, or early.
- Frequent replacement — Discarded 1 monthly/quarterly.
- Traditional (reusable) — Discarded6 monthly or later.
- Usually Gas Permeable GP lenses can last a year or longer as these are more resistant to lens deposits and don’t need to be discarded as early as soft lenses.
-
Contact Lens Wear and CareCare for your contact lenses by proper cleaning, disinfection and storage.
Till a few years ago, one needed several bottles of cleaning solutions for proper lens care but today, “multipurpose” solutions are available which help to both cleans and disinfect, and is also used for storage.
-