Scleral contact lenses have found an irreplaceable niche for managing corneal irregularity and ocular surface disease. Like any other type of contact lens, wearing them is not without risk of complications. Recently, there has been renewed concern about whether scleral lenses cause increases in intraocular pressure (IOP) during wear and shortly after removal (McMonnies, 2016).
Potential Mechanism of Increased IOP with Scleral Lenses
Scleral lenses are held in place by two forces that allow them to hold a fluid reservoir (Miller et al, 1968). The first force is surface tension that results from a liquid interface between the haptic and the anterior ocular surface. Surface tension allows the scleral lens to stick to the eye surface much like a glass will stick to the surface of a wet table. The other potential force is sub-atmospheric pressure or suction that can develop secondary to loss of fluid or lens settling (McMonnies, 2016). It is theorized that suction could lead to increased IOP, similar to documented cases using microkeratomes during refractive surgery procedures (Kasetsuwan et al, 2001).
Another mechanism that has been proposed is that the haptic of a fit scleral lens compresses episcleral veins and Schlemm’s canal, potentially decreasing outflow and resulting in increased IOP (Nau et al, 2016).
Research and Data
The first modern study to evaluate IOP during scleral lens wear measured IOP of 29 healthy subjects before, during, and after lens wear (Nau et al, 2016). A pneumatonometer was used to measure IOP with a scleral lens in situ. Results indicated that scleral lens wear did not increase IOP during and after wear; however, there were outliers that did show increased IOP.
In addition, a poster presented at the 2018 Global Specialty Lens Symposium meeting by Turpin et al showed data from a study also measuring IOP of 14 individuals during scleral lens wear. For this study, IOP was measured using a hand-held tonometer, which allows for IOP measurement over the lid with a scleral lens in place. This study reported an average of 7 mmHg increase during the course of scleral lens wear. And, a recent study by Michaud et al (2018) reported similar findings; it showed an average increase of 5 mmHg regardless of the scleral lens diameter worn.
Discussion
There are concerns regarding the accuracy of measurements taken with a scleral lens in situ. (Turpin et al, 2018). Lens manipulation and corneal swelling also can effect standard IOP measurements taken after removal (Schornack et al, 2012). If IOP is significantly increased with scleral lens use, then why aren’t there documented cases of IOP-related complications after decades of scleral lens prescribing?
Although additional studies are needed to assess the risk of increased IOP with scleral lens wear, there is enough evidence to suggest that practitioners should be cautious when prescribing scleral lenses for patient populations that are at risk for glaucoma. It is probable that fitting scleral lenses that adhere to the anterior segment with surface tension and little to no suction lowers the risk of suction-related IOP increase. Fenestrated lenses also may be a best-fit option for specific cases. CLS
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