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Sleep Posture Hacks: Head Elevation and Side-Sleeping Effects on Eye PressureHigh intraocular pressure (IOP) – the fluid pressure inside the eye – is a key factor in glaucoma and other eye diseases. Notably, IOP can change with sleep position. Studies show that simply lying down tends to raise IOP compared to sitting (). For example, one experiment found the average IOP was significantly higher when healthy subjects lay flat than when they sat up (). Over the course of the night, side-lying or stomach-lying positions can further affect pressure. In this article we explain how sleeping at a 20–30° head-up angle can lower nighttime eye pressure, why the “down-side” eye often has higher pressure when you sleep on your side, and how practical aids (wedges, adjustable beds, pillow stacks) compare. We also discuss comfort and adherence issues, caution about tight eye masks, and give a simple step-by-step plan for trying new sleep postures and checking the effect (for example with a home tonometer if you have one).Side-Sleeping and the Dependent EyeWhen you lie on your side, gravity and blood flow tend to increase pressure in the dependent eye – the one on the pillow side. In other words, your lower eye usually has higher IOP than your upper eye. Multiple studies confirm this dependent-eye effect. For instance, experiments with healthy volunteers and glaucoma patients show that the eye you lie on (the dependent eye) experiences a significantly greater IOP rise than the higher eye (). Even in people with one worse (more damaged) eye, that worse eye tended to have higher pressure if it happened to be on the pillow side (). Another study of glaucoma patients who habitually slept on one side found that the down-side eye’s IOP climbed about +1.6 mmHg after 30 minutes in that position (). (In eyes that were deteriorating on that side, the increase was even larger, around +2.5 mmHg ().) Over time such repeated pressure spikes on one eye could contribute to worsening glaucoma in that eye.The takeaway: if you sleep on your side, the eye on that side will typically show higher pressure overnight. Experts often recommend that glaucoma patients try to avoid lying on the “bad” eye side. Sleeping on the back (with head raised) keeps both eyes level and may help limit these asymmetric pressure bursts ().Why flat lying raises IOP tooIt’s worth noting that even flat supine sleep (lying on the back or stomach) raises IOP compared to sitting up. In the same head-elevation study mentioned above, investigators found standing/sitting IOP was lower than flat-lying IOP in all subjects (). This happens partly because lying down increases blood pressure in the head and heart, and this in turn raises eye pressure. The lay-flat effect is why simply elevating the head can lower IOP somewhat – as we will see next.Head Elevation and IOP ReductionSleeping on an incline (head up) has been shown to lower IOP a modest amount. A clinical experiment with patients sleeping in a lab found that a 20° head-up tilt (achieved with a wedge pillow) reduced average nighttime IOP by about 1.5 mmHg (around 9–10%) compared to lying fully flat (). In that study, 25 of 30 patients (over 80%) had lower mean IOP at 20°, and 36.7% had reductions of over 10% (). In real numbers the average drop was about 1.56 mmHg for glaucoma patients (from ~15–16 down to ~14 mmHg) and 1.47 mmHg in non-glaucoma people (). In plain terms, elevating the head by 20°–30° lowered nighttime eye pressure b