Contact lenses are optical devices.
These are use in as alternative for eyeglasses. They sit on the surface of the cornea. This is the reason why they are popular among sportsmen and person involve in a certain occupational situation where eyeglasses are not consider fit. They are gaining in popularity, and there is a steep increase in the number of lens wearers. Types of contact lenses uses for refractive correction mostly, but also for cosmetic, aesthetic and medical purposes.
Types of contact lenses
Hard rigid contact lenses:
The original contact lenses are also known as PMMA lenses (polymethylmethacrylate). They are virtually obsolete now and no longer in use. They were the first contact lenses that exist and are least hydrophilic. These types of contact lenses restrict the oxygen passing through the cornea and deplete the glycogen stores. But they provide a good refractive correction and are durable. In some cases of severe keratoconus, irregular astigmatism and some ocular surface disorders these types of contact lenses are still in use.
Soft contact lenses:
Also known as HEMA lenses (hydroxyethyl methacrylate). They are usually of silicone or hydrogels or a combination of both. They are hydrophilic materials and are compose of almost 80% water. These types of contact lenses are highly oxygen permeable and hence provide the best comfort while wearing. Though they do not provide the best refractive correction, they are hygienic and most popular among contact lens user. There are various types of contact lenses according to the frequency of usage. There are daily disposable, bi-weekly, monthly or yearly.
Gas- permeable rigid contact lenses:
These types of contact lenses are a combination of hard and soft contact lenses. These are the best contact lenses for astigmatism as they provide the best visual acuity. They are high gas permeable and do not deposit proteins easily. They are very durable and won’t tear up easily like soft contact lenses.
Gas permeable rigid lenses might not be comfortable immediately as they need a little time to be adjust with the eyes. They are perfect for astigmatism, presbyopia requiring bifocal and multifocal lenses, keratoconus, and people after refractive surgery or people who want to obtain the sharpest vision. They are even used for corneal reshaping and are worn while sleeping to shape the cornea to improve vision.
Gas permeable lenses are smaller in size than soft contact lenses. Certain disadvantages of these types of lenses are they are smaller there is a risk of displacing it if involve in sports or other activity. They move when the wearer blinks so there is a risk of dust and debris to deposit under the lenses.
Scleral Contact Lenses:
These lenses are large and rigid. These types of contact lenses form an arch over the cornea and rest on the sclera that is the reason why they are named Scleral contact lenses. They are usually prescribed to people suffering from keratoconus or has undergone cornea transplant, or people with extremely dry eyes conditions, irregular astigmatism, etc. Due to the large size of the lenses, it requires some practice to apply and remove the lenses.
Scleral contact lenses cost more than any other lenses because they require custom fit for each wearer. And also depending on the complication of the problem of each wearer the lenses requires adjustments. Fitting them also may take several visits to determine the optimal lenses for each eye. One more advantage of Scleral lenses is that they do not move while blinking, making it more stable than the other types of contact lenses.
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