Today when people hear of hard contact lenses they often think of uncomfortable lenses people wore before the advent of soft contact lenses. Recently though, there has been a resurgence of hard contact lenses. They are being used primarily for special cases such as keratoconus, post-surgery complications, cornea transplants, dry eye, myopia control, and others. These lenses are not “one size fits all” as many soft contact lenses are, and therefore, require special consideration for which lens to use, as well as extra time fitting; however, once the correct lens is selected, and the fit is completed, the result can be life-altering.
The edge of a traditional hard lens rests on the cornea, the sensitive part of the eye, which is why traditional hard contact lenses are initially uncomfortable. Scleral contact lenses, larger hard contact lenses, rest on the sclera which is not sensitive like the cornea and are therefore very comfortable the first time they are worn. Increased comfort is not the only advantage to “landing” on the sclera; the larger diameter allows the lens to vault the cornea, or go over it without touching it. This is especially advantageous for people who have keratoconus, post-surgery complications, corneal transplants, or any case in which we don’t want a lens touching the cornea.
The space between the cornea and the contact lens is filled with preservative free saline solution. The solution fills in the irregularities of the cornea, and creates a smooth regular refractive surface over the entire cornea. So, not only does the vault prevent the lens from touching the cornea, but it also results in better corrected visual acuity. Additionally, the preservative free saline solution between the cornea and lens makes scleral lenses a good option for patients who suffer from dry eye. The lens itself acts as a barrier to the environment, and the solution remains present to keep the eye lubricated.
Another lens that can be used for vaulting the cornea is the Ultra Health lens by SynergEyes. The Ultra Health lens is a combination of a traditional hard contact lens in the center, with a soft contact lens in the periphery. There are other lenses of this nature, termed “hybrid lenses,” but what makes the Ultra Health lens different is that it has a reverse geometry curvature. A normal cornea has the steepest curvature in the center of the eye, and becomes flatter, or less curved, peripherally. Most contact lenses follow this pattern to a degree. A reverse geometry lens; however, is less curved in the center, and then steeper in the periphery. The increased flatness of the center allows the lens to vault the cornea like a scleral lens, making it useful for people with irregular corneas also.
Reverse geometry curvature is also being used in traditional hard contact lenses for myopia control, or the prevention of the progression of myopia, or near-sightedness. These lenses are worn during the night and removed during the day. The forces of the reverse geometry curvature reshape the corneal epithelium, the outer layer of the cornea, in a way that produces an image on the retina that does not cause the eye to elongate, or progress in myopia. Another benefit of these lenses is that the reshaping results in the correction of the prescription, so that no correction is needed during the day. One disadvantage of these lenses is that they are initially uncomfortable to wear because they rest on the cornea. This does go away, however, once the eye adapts to wearing the lens.
Though most of our specialty lenses are hard contact lenses, there is at least one way in which soft lenses can be used as a specialty lens as well; and that is also for myopia control. Multifocal contact lenses, which are traditionally used for people who need reading correction as well as distance correction, also produce an image on the retina that does not cause the eye to elongate, or progress in myopia. Studies seem to indicate multifocal contact lenses are not quite as effective as using the reverse geometry curvature hard lenses, but they are still very effective, and much more comfortable.
If you have been told previously that contact lenses would not work for you, or you would just like to pursue a different contact lens option, the doctors at Eyecare Associates would be happy to discuss all of these modalities with you.