Covering Lens Coverage
Lynette Johns OD FAAO FSLS
Diameter is an important parameter when fitting scleral lenses. When selecting the diameter, consider the ease of application and removal, support of the sagittal depth, and fitting inside or around scleral obstacles. Knowing that the conjunctiva overlying the sclera is relatively insensitive compared to the cornea, is there any therapeutic value for increased surface coverage?
A 52-year-old female with a history of scleroderma and secondary Sjörgren’s syndrome complained of extreme ocular pain, photophobia and diminished vision. Her entering best corrected visual acuity was 20/40 OD and 20/30-2 OS. She applied topical lubricating drops every fifteen minutes and was also using cyclosporine drops BID with minimal to no relief. Figure 1 (below) shows an example of the baseline keratopathy.
Both eyes were fit with 18.0 mm diameter scleral lenses, and her pain and photophobia were immediately attenuated. After dispensing the scleral lenses, her vision improved to 20/25-2 OD and 20/20 OS. She was advised to continue lubricating drops over the lenses. When the lenses were removed, her corneal staining pattern diminished dramatically (Figure 2, below).
Interestingly, there is a sharp demarcation line between the conjunctiva that was protected by the scleral lens and the exposed conjunctiva, which exhibited staining. As with the improvement in corneal staining with constant lubrication, perhaps there is a therapeutic effect of scleral lenses on the conjunctiva as well (figure 3, below).
There are many advantages of both small and large diameter scleral lenses. Selecting the diameter for the patient can be a challenging decision. For instance, if the scleral topography has asymmetry, then selecting a small diameter may be more advantageous. Otherwise, using a larger scleral lens on an eye with scleral asymmetry may require toric or quadrant specific back surface curves in the lens designs for proper alignment; in doing so, the fit may become more complicated.
Some patients who have ocular surface disease request their lenses to be made larger because they are symptomatic beyond the edge of the lens. Their most common symptom is feeling dryness that topical lubricants cannot relieve. They are asking for more coverage. Once refit to a larger diameter scleral lens, their symptoms lessen. Often, scleral topography dictates which scleral lens diameter to trial. However, in this case, there was a reduction in conjunctival staining beneath the scleral lens. Ultimately, if the patient is comfortable during all waking hours, and the ocular physiology is not compromised, then the fit is deemed successful. Should this therapeutic effect also be a consideration to use a larger diameter? How large do you make the lens? There is still a lot we need to learn about scleral lenses and parameter selection.
Dr. Lynette Johns is an adjunct assistant professor and clinical attending in contact lenses at the New England College of Optometry.
She was formerly the senior optometrist at the Boston Foundation for Sight where she exclusively fit scleral lenses and managed complex corneal disease.
She is a fellow of the American Academy of Optometry and Scleral Lens Education Society as well as a member of the BCLA. She is a clinical and educational consultant to the GP and specialty soft lens division of Bausch + Lomb.