A Brief History of Scleral Lenses
Scleral lenses were actually the first contact lenses described in medical literature in the late 1800’s. Adolf Fick described his use of blown glass “vesicles” in 1888. Eugene Kalt’s use of a glass “contact shell” to improve vision in a patient with keratoconus was reported in 1888. As part of his doctoral dissertation, August Mueller described his attempts to correct his own high myopia with ground glass lenses in 1889. The manufacturing process necessary to create these early lenses was challenging, and wearing the lenses quickly caused symptoms of oxygen deprivation. Although these early lenses did improve vision, manufacturing and wearing challenges proved to be initially insurmountable, and scleral lenses were not widely used.
The development of polymethylmethacrylate (PMMA), a new lens material, in the early 1900’s made it somewhat easier to manufacture lenses. PMMA is moldable, and could be used to make a lens based upon an impression mold of the surface of the eye. However, the manufacturing process was still very cumbersome. It was virtually impossible to reproduce lenses reliably. Furthermore, PMMA was not oxygen-permeable. In order to allow oxygen to reach the cornea (the clear dome of tissue that covers the surface of the eye), fenestrations, or holes, were made in the lenses. These fenestrations allowed air to enter the space between the back of the lens and the front of the eye. Unfortunately, bubbles led to dryness of the eye’s surface. Although PMMA lenses were better than glass shells, challenges certainly remained.
In the mid-1900’s, corneal contact lenses were introduced. Original corneal lenses were made of PMMA, but were much smaller than scleral lenses. Since they didn’t cover the entire cornea, oxygen could reach at least part of the front surface of the eye. The movement of corneal lenses on the front surface of the eye with each blink also facilitated regular exchange of tears beneath the lenses. The lenses were easier to fit than scleral lenses; diagnostic fitting lenses replaced impression molding of the front surface of the eye in the fitting process. Although early manufacturing techniques were far from perfect, it was easier to accurately produce corneal lenses. The development of corneal lenses continued with the introduction of rigid gas permeable materials. These materials allowed for exchange of oxygen through the lenses themselves, and further reduced complications of contact lens wear related to lack of oxygen to the cornea.
When hydrogel (soft) lens materials were introduced in the 1960’s and 1970’s, demand for contact lenses as a means for correcting vision increased even further. Early soft lenses were “breathable” (or oxygen-permeable) to some extent, and could therefore cover the entire cornea and extend onto the sclera (the white tissue that forms the outer wall of the eye) without severely damaging the surface of the eye. Hydrogel lenses offered less initial lens awareness than corneal rigid gas permeable lens designs. Silicone hydrogel lenses, introduced in the late 1900’s, rival rigid gas permeable materials in oxygen transmissibility, offer initial comfort similar to other hydrogel lenses, and are now available to correct nearsightedness, farsightedness, astigmatism, and presbyopia.
In spite of the vast improvements in both corneal rigid gas permeable lenses and hydrogel lenses, several eye care providers saw a continued need for large-diameter lenses. The 1970’s saw the first reports of the use of rigid gas permeable lens materials in the manufacture of scleral lenses. Since then, there has been a slow but steady increase in interest in scleral lenses. Modern rigid gas permeable lens materials allow for longer, more comfortable wear (often without fenestrations), and the maintenance of a fluid reservoir behind the lens. Standardized lens designs make it easier to fit large-diameter lenses without the need to obtain an impression mold of the eye’s surface. Significant improvements in manufacturing processes (computer-assisted manufacturing and more repeatable lathes) have made it possible to accurately reproduce lenses.