Scleral contact lenses are not new, and in fact are a very old type of contact lens, but although they almost vanished into oblivion, they are now making a comeback.
Scleral contact lenses are big! I don't mean that in the sense that they are popular but rather they are physically large. The white part of the eye is called the sclera and these lenses are supported by this structure. The smallest of these lenses will cover the entire colored part of the eye and will then extend a small amount onto the white part of the eye. The largest of these lenses will continue to extend onto the white of the eye so that every part of the eye that is showing and even some parts that are hidden by the lids, will be covered by this lens.
Scleral lenses are not new. The concept of contact lenses in general dates back to the 1500s and Leonardo da Vinci. As with many of da Vinci's inventions, he was way ahead of his time and there was no practical way to manufacture his contact lens. Blown glass were some of the early models and a great deal of work with this was done throughout the 1800s. Toward the end of the 1800s glass scleral lenses were being made but their use was very limited as glass was not a very good material to use on eyes. In the 1930s, the plastic, polymethylmethacrylate was invented and much progress was made with contact lenses. The scleral lenses were originally "cast" from an impression molding technique much the same way that dentists currently impression mold teeth. For non-sighted eyes today, this technique is still used to create a scleral shell. This shell is a lens that covers the eye in its entirety that is hand-painted to cosmetically match the other eye. For sighted eyes however, the technique of impression molding has given way to more modern techniques using diagnostic sets of lenses for fitting purposes and very sophisticated computer-driven lathes for manufacturing. The remainder of what is discussed here will be with regard to this latter type of scleral lens.
The size of scleral lenses introduces additional concerns regarding the normal physiology of the cornea and the eye. Only the more oxygen-porous gas permeable materials are used to ensure an adequate supply of oxygen for the cornea. Handling the lenses is rather easy since they are so large, but application and removal of the lenses to and from the eye can be a bit trickier than conventional contact lens designs. Sometimes, to aid in removal as well as aid in tear flow under the lens, the lens may be fenestrated. This means that near the lens edge, there will be placed one, two or three small holes. The materials chosen are generally clear. This is because a lens with color will show on the white part of the eye which for most people is cosmetically undesirable.
The fitting process as well as the manufacturing process is quite a bit more challenging with this class of lenses. This fact along with the fact that mass-production of these types of lenses is not possible, means that their costs can be significantly higher than the traditional contact lenses of today. There is also more time required when fitting these lenses. This means more time for the physician, more time for the patient, and more time for the laboratory actually manufacturing the product.
Due to all of the above reasons, scleral lenses are not utilized in a routine fashion. These very unique products however, do have their place. For corneas that have become irregular, scleral lenses can sometimes outperform other types of contact lenses. An irregular cornea can be the result of a disease such as Keratoconus, corneal trauma, corneal transplant, and more recently refractive surgery (i.e. RK , AK , ALK , PRK , LASIK, LASEK , iLASIK , ICR ). In many cases, the irregular cornea prevents the proper positioning of a corneal lens but a scleral lens can seat itself properly on the sclera and therefore be in the correct position on the cornea. The vision with a scleral lens as well as the other gas permeable corneal lenses can be vastly superior to glasses or soft contact lenses especially when considering irregular corneas. These lenses provide the optical system a new surface that provides great vision while neutralizing all of the irregular optics of the underlying cornea. For many people with irregularly shaped corneas, these types of lenses provide the only form of usable vision correction.
Additionally, scleral lenses can address many contact lens failures that were secondary to dryness. Since the scleral lenses are so large, there forms a tear reservoir under the lens that can keep the cornea properly moist. Foreign matter and debris also have a very difficult time finding their way underneath one of these lenses. This fact can be the single entity that allows contact lens success while all other contact lenses have failed.
Whenever I show a scleral lens to a patient for the first time the patient's reactions are almost always the same. The comment is always something to the effect "Are you planning on put that huge thing in my eye?!" This is followed with "How much is it going to hurt?" The surprising and good news is that the scleral lenses are extremely comfortable right from the beginning. Due to their size, contour, and limited movement, there is virtually no sensation at all.
Although scleral lenses will clearly not become the lens that dominates the contact lens market, when the need is there, this lens can often solve problems that are unsolvable through any other means. The scleral lens will continue to serve a unique role for some very unique situations.