There is no question that modern scleral lenses have revolutionized specialty contact lens practice. Their comfort is certainly superior to corneal GPs, at least initially. I love sclerals and fit them a great deal of the time, but I also still fit lots of corneal GP lenses. Many contact lens experts on the continuing education circuit still advise trying corneal lenses first if possible. Below, I have outlined a few reasons that favor the use of corneal GP lenses.
1) Oxygen Delivery
A huge advantage of corneal GPs lies in the oxygen transmissibility of the lens and tear film. While sclerals are manufactured in high-Dk materials, it is the Dk/t (transmissibility) that matters. A typical 300-micron-thick scleral lens combined with a 200-micron tear film simply cannot compete with a 120-micron-thick corneal lens and 20-micron tear film in terms of oxygen transfer.
Theoretical calculations and in vivo measurements point to a typical scleral lens Dk/t in the range of 20 barrers—quite low compared to other lens options (Giasson et al, 2017). A corneal lens doesn’t cover the entire cornea, either, leaving some of the cornea exposed to the atmosphere. It is critical to consider oxygen transmissibility when choosing the best lens for your patients.
2) Ease of Care and Use
Taking care of corneal GP lenses is inexpensive and easy; often, only one multipurpose solution is needed. Corneal GP lenses can typically be easily applied and removed with no special devices required.
Scleral lenses may require extra cleaning steps as well as single-use, nonpreserved saline solution to fill the bowl prior to application. They often are applied and removed using suction cups, which must also be cleaned and cared for. Patients should take care solutions, application solutions, and suction cups with them in case they need to handle their lenses away from home. The large size of scleral lenses can make them difficult to apply for some patients, too.
3) Cost of Lenses
Corneal GP lenses are, in general, less expensive for both the lenses themselves and for the care products compared to scleral lenses. With healthcare costs rising, this is an important consideration.
Even if insurance coverage for the initial lenses is available, patients will still have to purchase replacement lenses on occasion, and the price of scleral lenses can be a burden for some patients.
One advantage of scleral lenses is that they bridge over any irregularity of the cornea, often simplifying the fitting process. But, standard corneal lenses can typically work on a wide range of irregular corneas as well. And, toric, oblate, and quadrant-specific designs are also available for more challenging corneal shapes. With topography data, your GP lab can help you design a well-fitting corneal GP lens for most irregular corneas.
Use All of Your Options
We are living in a wonderful age of specialty contact lenses, and we have a much bigger toolbox of options to choose from than ever before. Scleral lenses are, and should be, a major component of our practices. But, don’t forget the time-honored contact lenses that got us here…corneal GPs! CLS
For references, please visit www.clspectrum.com/references and click on document #264.