The Impact of Scleral Lenses on Intraocular Pressure

<b>Background:</b> In 2016, Charles McMonnies advanced a theory positing that the use of scleral lenses might result in an elevation of intraocular pressure (IOP) due to the compression of the episcleral veins, consequently diminishing the eye's capacity for draining aqueous humor. Alternative drainage pathways are capable of compensating only for 10-30% of the aqueous humor that requires drainage. Then it remains a quantity of fluid trapped in the anterior chamber. Recent data has demonstrated that the scleral lenses wear results indeed in an augmentation of the anterior chamber volume and a reduction of the iridocorneal angle, concomitant with a compression of Schlemm's canal. Assuming that aqueous humor production remains constant, this imbalance between inflow and outflow can only lead to an increase in intraocular pressure. <b>Methods:</b> Several studies have attempted to answer this question over the past 10 years. Most authors have encountered the inherent difficulty of measuring IOP while the lens is still in place. Others were performed without waiting for the required time (>4 h of wear) for the lens to exert its maximum compression, thus minimizing their impact. Some attempted to assess IOP via the sclera (pneumotonometry), a technique known to give variable results and hard to reproduce. Ultimately, there are few reliable ways to assess IOP. One of them is by directly observing changes in the optic nerve structure over time. <b>Results:</b> These works indicate that there is indeed a moderate increase (<5 mmHg) in IOP. Could this be causing neuropathy and long-term negative impacts for patients who may be at risk? Based on the clinical experience of those involved in the field for many years, it is unlikely that IOP variations may have an impact on a healthy optic nerve. However, glaucoma patients or those at risk could be adversely affected in the long term. <b>Conclusions:</b> It is still too early to determine, without a doubt, the actual impact of the likely increase in IOP resulting from the structural changes caused by wearing scleral lenses Further work is therefore urgently needed to document these longitudinal changes.