Anatomical and physiological considerations in scleral lens wear: Intraocular pressure

Intraocular pressure (IOP) is maintained through complex and interrelated systems which control aqueous production and drainage, and it has been suggested that scleral lens (SL) wear may disrupt these vital homeo-static processes. This review provides an overview of anatomical and physiological processes that control IOP, identifies potential effects of SLs on these regulatory mechanisms, and examines studies that have attempted to quantify the effect of SLs on IOP. Lack of access to the cornea during SL wear makes accurate assessment of IOP challenging; therefore, a range of different assessment techniques and instruments have been employed to quantify IOP during and following SL wear. Some studies have evaluated IOP using standard techniques prior to lens application and following lens removal, or through a large central fenestration. Other studies have utilised instruments that facilitate assessment of IOP on the peripheral cornea or conjunctiva overlying the sclera (e.g. Schiotz, transpalpebral, and pneumatonometry). Two studies have recently evaluated changes in optic nerve structure during SL wear. Conflicting results have been reported on this topic, much of which examines changes in IOP in healthy subjects over limited periods of time. Currently, only a few studies have reported on long-term effects of SL wear on IOP in habitual SL wearers (after lens removal). Future research in this area must not only consider the fact that ocular conditions treated with SLs may potentially alter corneal biomechanical properties which can influence IOP, but also that these properties may be further altered by SL wear. Monitoring other risk factors for glaucoma (permanent alterations in optic nerve physiology, visual field defects) could provide a more comprehensive assessment of potentially increased risk of glaucomatous optic neuropathy due to SL wear. Ongoing clinical assessment of optic nerve structure and function is advisable in patients at risk for glaucoma who require SLs.

Automated summary

Intraocular pressure (IOP) is regulated by complex systems and the use of scleral lenses (SLs) may disrupt these processes. This review examines the anatomical and physiological control of IOP, explores the potential effects of SLs on these mechanisms, and analyzes studies that have attempted to measure the impact of SLs on IOP. Accurate assessment of IOP during SL wear is challenging, but various techniques and instruments have been used to measure IOP before and after lens application, as well as on the peripheral cornea or conjunctiva overlying the sclera. Some conflicting results have been reported regarding changes in IOP during SL wear, particularly for short durations. Long-term effects of SL wear on IOP in habitual wearers are still under-researched. It is important to consider the impact of SLs on corneal biomechanical properties and monitor other risk factors for glaucoma in SL wearers.