Contact Lens Case Reports

How Much Tear Exchange Occurs Beneath Scleral Lenses?

BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO

How much tear exchange takes place beneath modern scleral lenses? To address this question, we evaluated two series of three similar cases. In the first series, a 16.5mm scleral lens was placed onto the right eye, using fluorescein dissolved into preservative-free (PF) saline as the application solution. Patients wore the lens for a period of eight hours, and cobalt blue photography was performed at 30 minutes and at one, two, four, six, and eight hours. Anterior segment optical coherence tomography (OCT) was performed at each time point to monitor settling.

Subjective observation showed little or no dilution of the fluorescein throughout the eight-hour period (Figures 1 and 2).

Figure 1. In this patient from the first case series, cobalt blue photography was performed at 30 minutes, one, two, four, six and eight hours.

Figure 2. The luminance of the fluorescein immediately following lens application and following eight hours of lens wear. The eight-hour white light image showed no conjunctival injection.

In the second series, scleral lenses filled with clear PF saline were placed onto one eye and photographed with white and cobalt blue light. Following 30 minutes of lens “settling,” PF fluorescein drops were instilled onto the superior bulbar conjunctiva every 20 minutes for eight hours (total 23 drops). At eight hours, the amount of fluorescein beneath the lens was photographed and subjectively compared to the baseline images.

Subjective observation of the cobalt blue images showed little or no fluorescein beneath the lens following eight hours of lens wear (Figure 3).

Figure 3. In this patient from the second case series, following 30 minutes of lens “settling,” PF fluorescein drops were instilled onto the superior bulbar conjunctiva every 20 minutes for eight hours (total 23 drops).

Closing in on the Answer

It appears from these two case series that minimal tear exchange takes place into or out of scleral lenses that rest solely on the bulbar conjunctiva. We hypothesize that shortly after scleral application, it “sinks” into the boggy bulbar conjunctiva (43μm within 30 minutes), creating a semi-closed solution reservoir under the lens.

More advanced techniques are needed to more accurately measure post-lens tear exchange as well as to quantify the compositional changes of the tear film/application solution during lens wear. The characterization of the “non-mobile” post-lens solution has important implications as we develop advanced application products designed to address the needs of the underlying ocular pathology being treated. CLS

The authors thank Sheila Morrison and Maria Walker, OD, MS, for their work with these case series.

Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Contamac. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.