In recent years, concern has been raised regarding the effects of scleral contact lens wear on intraocular pressure (IOP). Many theories have been proposed regarding mechanisms for potential scleral lens-induced IOP changes, including compression of episcleral veins (Nau et al, 2015), disruption to angle and trabecular meshwork anatomy (McMonnies, 2016), and suction forces beneath the scleral lens (Vincent et al, 2017), an example of which might be conjunctival prolapse.

Challenges in methodology have limited research in this area, as few techniques are available for measuring IOP during scleral lens wear. In a study by Nau et al (2015) using pneumotonometry, they found no significant change in IOP after two hours of wear, measured on the sclera.

A Case Series

In a case series, five consecutive healthy patients aged 24 to 25 years old with no previous history of scleral lens wear were fitted with 16.3mm diameter scleral lenses. All IOP values were measured with a transpalpebral scleral tonometer (Diaton, BiCom Inc.), allowing for measurements to be taken during contact lens wear (Figure 1).

Figure 1. IOP measurements using the Diaton device. IOP is measured through the superior lid, which should be retracted to approximately 1mm beyond the limbus.

Baseline IOP measurements were taken without lenses at 8:00 a.m., 10:00 a.m., and 4:00 p.m. The following day, the scleral lenses were applied at 7:55 a.m., and the IOP was measured after five minutes, two hours, and eight hours.

Three IOP measurements were taken and averaged at each time period. IOP measurements taken without lenses were compared to those taken with lenses at corresponding times.

In some patients, the measurements with the Diaton device were highly variable, especially during contact lens wear. The measurements presented are from only two (of five) cases in which the recommended measurement technique was possible with scleral lens wear due to ocular anatomy.

In these two patients, a small increase in IOP with scleral lens wear was found at all three readings. Figures 2 and 3 illustrate the IOP differences found in the two patients.

Figure 2. Patient 1 right and left eye measurements.

Figure 3. Patient 2 right and left eye measurements.

The significance of these findings is unclear, and conclusions cannot be made due to the small number of cases. This case series illustrates the difficulty, yet importance, of determining reliable methods for measuring IOP during scleral wear.

The transpalpebral scleral tonometer described above was not designed for use during contact lens wear, and the technique adjustments made to achieve measurements may have created some variation in the data.

Using the Diaton during scleral lens wear was further complicated by anatomical variations in eyelids and orbits, the relatively large size of the contact lens, and patients flinching during measurements (Doherty et al, 2012).

Studies are warranted regarding this topic, and novel techniques may be required to assess IOP during scleral lens wear. Indirectly measuring IOP via episcleral venous blood flow (Funk et al, 1996) or via 24-hour monitoring devices should be considered. CLS

The authors would like to thank Dr. Emily Korszen for her work with this case series.

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