Effect of Sleeping in a Head-Up Position on Intraocular Pressure in Patients with Glaucoma

I am reading this study now. I like the fact that they did investigate ocular perfusion pressure (OPP) while monitoring the intraocular pressure (IOP) during this study, and that they checked IOP in the sleeping position (rather than sitting the patient up). So, with a quick glance, the methodology looks acceptable to me.

Purpose: To determine whether a 30-degree head-up sleeping position decreases nocturnal intraocular pressure (IOP) compared with lying flat in patients with glaucoma.