Could contact lenses that sit on your sclera (rather than your cornea) be the secret to long-term comfortable lens wear? This post explains what these lenses are and how they work.
Traditionally, contacts have been designed to sit on your cornea – the clear dome at the front of the eye. They come in hard and soft materials and, as the name suggests, they are fitted to contact the front surface of your cornea.
The highly sensitive cornea
The cornea is the most sensitive part of your body. It is packed with nerves that register touch and pain. In fact, the density of pain receptors in the cornea of your eye is 600 times greater than skin, and 40 times greater than dental pulp! Even the constant rubbing from a contact lens, can cause discomfort and this is a key reason why so many people fail in their lenses over time.
What are scleral lenses?
The sclera is the white of your eye. It’s a tough rubbery layer that holds the eye together. Unlike the cornea (or central clear window to your eye) the sclera is not very sensitive to touch. You can easily try this for yourself by placing a clean fingertip (no long nails!) on the white of your eye.
Scleral contact lenses are hard, like rigid gas permeable (RGP) lenses. But unlike their smaller relations, they extend onto the white of your eye and bear all their weight on the sclera, completely vaulting over the super-sensitive central cornea. They also trap a layer of fluid over the cornea, constantly bathing it in tears.
This can make them very comfortable for people who have failed in other contact lenses (soft or hard) or who suffer from debilitating dry eye syndrome.
Who gets scleral lenses?
These lenses are more expensive than a pair of regular hard or soft lenses and much trickier to fit successfully. They need to be fitted by a contact lens specialist who is experienced in working with these lenses every day – not just a couple of times a year.
For these reasons, scleral lenses are rarely the first lens you will be fitted with. They are usually reserved for when other lenses have failed to provide comfort and clear vision. But when there is an irregular cornea (such as after a corneal transplant or in diseases like keratoconus) these lenses can be the ultimate in comfort. They completely bypass the sensitive central cornea, which is bathed in the pool of tears that lies beneath the lens.
They are also a viable treatment for severe, debilitating dry eye syndrome. By completely protecting your tear layer from evaporation and retaining it right where you need it, your cornea remains hydrated throughout the time the lenses are worn. These lenses can literally give people back their quality of life by allowing them to do things they haven’t been able to do due to the debilitating effects of dry eye. Activities such as watching television, play sports, travel on airplanes and other things we take for granted.
Are scleral lenses becoming more popular?
Yes. Years ago, these lenses were rarely fitted due to lack of availability of good designs and lack of expertise in fitting them. In the last decade or so, we have seen the arrival of much better designs and materials, which means many more people can enjoy their benefits than in the past.
What’s not to like?
These are often reserved for when less expensive or easier-to-fit lenses have failed. While they provide comfort and clear vision when fitted correctly, they can take some getting used to. Insertion and removal can be tricky and require practice and motivation. They are also more expensive on average than other options. Finally, not everyone is keen on the idea of putting something as large as a scleral lens into their precious eyes!
Are scleral lenses used for cosmetic purposes?
While custom soft contact lenses are sometimes used for cosmetic purposes (such as to cover up ocular scarring or deformity), hard lenses (including sclerals) are not suited to this purpose.
These lenses can do a lot of harm if not fitted correctly! A very worrying trend we have seen in the past year or two is the sale of cosmetic scleral lenses over the Internet. These lenses not only starve the cornea of vital oxygen, but, if not fitted correctly, can cause corneal abrasions and eye infections which could lead to scarring and permanent loss of vision. Never take risks with your most precious sense – your eyesight.