Many contact lens practitioners have witnessed the subjective and objective rehabilitation that takes place in dry eye patients wearing modern scleral lenses (Figure 1). A fundamental question is: How do scleral lenses do this for the wide range of patients who have ocular surface disease (OSD)?
It is well known that shortly after a scleral lens is placed onto the eye, a significant suction (negative pressure) force is created that results in substantial capillary attraction between the lens and the bulbar conjunctiva. The adhesion is so complete that it creates a water-tight seal (Figure 2), preventing the exchange of fluids out of or into the reservoir under a scleral lens.
Seeing Is Believing
This was demonstrated in two case series performed by Dr. Sheila Morrison at Pacific University. In the first case series, a scleral lens was placed on the right eye of three patients, using fluorescein dissolved into preservative-free (PF) saline as the application solution. Patients wore the lens for eight hours; it was photographed at 30 minutes and at one, two, four, six, and eight hours. Anterior segment optical coherence tomography (AS-OCT) was performed at each time point to monitor lens settling. The average amount of lens settling in the three patients over the eight hours was 133µm. There was little or no fluorescein exchange throughout the eight-hour period (Figure 3).
In the second case series, scleral lenses filled with clear PF saline were placed onto one eye of three patients and photographed with white and cobalt blue light. Following 30 minutes, PF fluorescein drops were instilled onto the superior bulbar conjunctiva every 20 minutes for eight hours (23 drops total). At eight hours, the amount of fluorescein beneath the lens was photographed and compared to the baseline images. OCT was performed at baseline and at eight hours to monitor lens settling. The average amount of settling in the three patients over eight hours was 123µm. The cobalt blue images showed no fluorescein under the lens following eight hours of wear.
What It Means
It would appear that shortly following scleral lens application, the resulting suction forces seal the lens onto the conjunctiva, and little or no tear exchange takes place. If this truly reflects what is taking place beneath well-fitted scleral lenses, the rapid rehabilitation of corneas that have severe OSD is simply a case of prolonged hydration with PF saline.
Studies are required to better quantify the tear exchange beneath scleral lenses and to clarify the compositional changes of the solution during lens wear. We believe that characterization of the post-lens fluid has important implications in better understanding the environment beneath modern scleral lenses. CLS