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Evidences from recent studies on 24-hour intraocular pressure (IOP) in sleep laboratories and from home recordings using a contact lens sensor have showed that for most glaucoma patients the nocturnal IOP during the sleep period is higher than the diurnal IOP during the wake period. However, there is a general lack of evidence whether or not a high sleep IOP, like high office-hour IOP, plays a role in
There is a general lack of evidence whether or not a high sleep IOP, like high office-hour IOP, plays a role in glaucoma pathogenesis
glaucoma pathogenesis. Seeking such evidence in clinical trials will involve very significant number of patients, repeated 24-hour IOP recordings, a long follow-up period, and high cost. One would be hesitant to take this task unless a strong indication appears that sleep IOP indeed plays a role. Although indirectly, the current report by Kim et al. may provide a timely support for the quest. The authors enrolled 692 patients with either bilateral normal-tension glaucoma (510) or bilateral high-tension glaucoma (182) in this cross-sectional study. They asked participants about their sleep body positions and determined the asymmetric visual field loss between the paired eyes in a masked fashion. Among the 430 patients (62% of total enrollment) showing an asymmetric visual field loss of at least 2 dB, 132 patients had a preferred lateral decubitus sleep position on the right side or the left side. Two thirds of these 132 patients slept on the same side as the worst glaucomatous damage occurred. A critical observation is that for the enrolled normal-tension glaucoma patients their office-hour IOP, refractive state, axial length, and central corneal thickness of the paired eyes are almost identical. While systemic confounding factors probably affect the paired eyes equally, an asymmetric visual field loss must be locally originated. Although related sleep IOP level was not measured in the current study, it is known that a small, but significant IOP difference exists between the paired eyes. The lower (dependent) eye in the lateral decubitus sleep position has a higher IOP than the upper eye. Results from the current study give a boost for those seeking further understanding of the link between sleep IOP level and glaucoma pathogenesis in prospective clinical trials. Fortunately, wireless technologies for monitoring sleep body position using a mobile device and for monitoring IOP using a contact lens sensor are fast advancing and would help this important quest in glaucoma research.