Why a Normal Eye Pressure Reading Can Still Miss Glaucoma: What New Nighttime Research Shows

Name: Why a Normal Eye Pressure Reading Can Still Miss Glaucoma: What New Nighttime Research Shows
Creator: Marc Shomer, MD, PhD
Published: 2026-08-29

August 29, 2026 · Written & medically reviewed by Marc Shomer, MD, PhD

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Eye pressure measurement during a glaucoma screening examination at Inland Glaucoma Center in Upland, CA

“Your pressure looks fine.” It is one of the most reassuring sentences a patient can hear at an eye exam, and one of the most misunderstood. An eye pressure reading taken in an office chair at 10 a.m. is a single snapshot of a number that rises and falls around the clock. For many people, the highest pressures of the entire day occur overnight, while they sleep. That is the one time no one is measuring.

New research published in August 2026 has now traced one of the biological switches behind that nighttime rise. It is a good moment to explain why glaucoma specialists have never trusted a single pressure reading, and what we do instead.

Eye Pressure Is a Moving Target

Intraocular pressure (IOP) is not a fixed number like your height. It fluctuates with time of day, body position, fluid intake, and the eye’s own circadian biology. Landmark sleep-laboratory studies measuring pressure around the clock found that in most people, with or without glaucoma, IOP peaks during the nocturnal period, typically in the early-morning hours before waking.

Two factors drive this:

Body position. Lying flat shifts fluid toward the head and raises IOP by several mmHg compared with sitting upright, which is the position in which pressure is always measured at the office.
Circadian biology. The eye’s fluid drainage changes overnight under the control of the body’s internal clock and stress-hormone signaling, so pressure can climb even before position is taken into account.

The practical consequence: a patient whose office reading is a comfortable 16 mmHg may be spending hours every night at 21 or higher, and neither the patient nor a routine exam would ever know.

What the New 2026 Research Found

In a study published in Communications Biology in August 2026, researchers identified a specific molecular pathway behind the nocturnal pressure rise. In laboratory animals, the stress hormone norepinephrine activates a signaling protein called RHOB in the eye’s drainage tissue at night, stiffening the outflow pathway and pushing pressure up during the nocturnal period.

Why does a mouse study matter to patients in Upland? Two reasons:

It explains a blind spot. The authors point out that because pressure tends to be lower during clinic hours, routine daytime checkups can miss the warning signs entirely. It is the same gap glaucoma specialists work around every day.
It points toward future treatments. If nighttime pressure spikes run through an identifiable pathway, that pathway becomes a drug target. A therapy aimed specifically at nocturnal IOP would fill a genuine gap, because not all of today’s treatments work equally well at night.

The Patients This Matters Most For

This blind spot is especially relevant in normal-tension glaucoma, the form of the disease in which the optic nerve shows unmistakable glaucoma damage even though every office pressure reading is “normal.” Nocturnal pressure peaks are one of several proposed explanations for why these nerves are being damaged despite reassuring daytime numbers.

It also matters for patients with ocular hypertension being watched without treatment, and for treated glaucoma patients who seem to progress despite “good” pressures at every visit. When the damage doesn’t match the numbers, the numbers, not the damage, are usually the incomplete part of the story.

How We Catch What a Single Reading Misses

At a dedicated glaucoma practice, no treatment decision rests on one measurement. The tools we use to see around the daytime blind spot include:

Pressure profiles across visits. Measuring IOP at different times of day on different visits sketches each patient’s personal pressure curve rather than a single point on it.
Corneal thickness. A thin cornea reads falsely low. A “normal” 15 mmHg on a thin cornea may not be normal at all.
OCT imaging of the optic nerve. Structural scans detect nerve-fiber thinning years before a patient notices anything, whatever the pressure readings say.
Visual field testing. Functional testing shows whether the nerve damage is actually affecting sight, and whether it is progressing.

The optic nerve keeps an honest 24-hour record even when our pressure measurements can’t. Tracking the nerve itself, structurally and functionally, is how glaucoma is caught and controlled despite the nighttime blind spot. That is the core of a proper glaucoma evaluation.

Treatments That Work Around the Clock

The nighttime story also shapes how we treat. Not all pressure-lowering treatments perform equally overnight:

Prostaglandin drops (such as latanoprost) lower pressure through the full 24-hour cycle, one reason they are first-line therapy. Timing and technique still matter; see our guide to why eye-drop timing and technique matter.
Beta-blocker drops (such as timolol) work mainly by slowing fluid production, which the eye already slows at night on its own, so their nighttime effect is limited.
Selective laser trabeculoplasty (SLT) improves the drain itself, so its effect does not depend on remembering a bedtime drop. The six-year results of the landmark LiGHT trial show over 70% of eyes treated with SLT first remained drop-free, with slower visual-field loss than eyes started on drops.

The Bottom Line

A normal eye pressure reading at a routine visit is genuinely good news, but it is not, by itself, an all-clear. Pressure often peaks overnight, when it is never measured, and new research is now mapping the biology of exactly how that happens. This is why glaucoma care at a specialty practice is built on the whole picture: pressure patterns, corneal thickness, the drainage angle, and, above all, direct structural and functional tracking of the optic nerve over time.

If you have been told you have glaucoma, suspected glaucoma, ocular hypertension, or a family history of the disease, and especially if your nerve findings have ever seemed out of step with your pressure readings, a comprehensive evaluation with a glaucoma specialist can look past the snapshot.

References

Ficarrotta KR, et al. Norepinephrine-induced small GTPase RHOB mediates nocturnal intraocular pressure rise. Communications Biology. August 2026. (Reported: “Why glaucoma risk may be missed by day,” MedicalXpress, August 2026.)
Liu JH, Kripke DF, Twa MD, et al. Twenty-four-hour pattern of intraocular pressure in the aging population. Investigative Ophthalmology & Visual Science. 1999;40:2912.
Gazzard G, Konstantakopoulou E, Garway-Heath D, et al. Laser in Glaucoma and Ocular Hypertension (LiGHT) Trial: six-year results. Ophthalmology. 2023;130(2):139.
Gedde SJ, Vinod K, Wright MM, et al. Primary Open-Angle Glaucoma Preferred Practice Pattern®. American Academy of Ophthalmology. 2025 Update.

Frequently Asked Questions

Can I have glaucoma even if my eye pressure is normal?

Yes. In normal-tension glaucoma, the optic nerve shows typical glaucoma damage even though pressure measured in the office is within the statistically normal range. One contributing explanation is that eye pressure fluctuates throughout the 24-hour day and often peaks overnight or in the early morning, hours when it is never measured during a routine visit. That is why glaucoma specialists never rely on a single pressure reading alone.

Why is eye pressure higher at night?

Two main factors contribute. First, lying flat redistributes fluid toward the head and raises pressure inside the eye compared with sitting or standing. Second, the body’s own circadian biology changes how fluid drains from the eye overnight. Research published in August 2026 identified a specific signaling pathway, the stress hormone norepinephrine acting through a protein called RHOB in the eye’s drainage tissue, that drives the nighttime pressure rise in laboratory studies, which may open the door to future treatments that target nighttime pressure directly.

How do glaucoma specialists catch pressure problems a single visit can miss?

Several ways: measuring pressure at different times of day across visits (a diurnal pressure profile); factoring in corneal thickness, which affects the accuracy of readings; examining the drainage angle with gonioscopy; and, most importantly, tracking the optic nerve itself with OCT imaging and visual field testing. Structural and functional testing shows whether damage is actually occurring, regardless of what any single pressure reading says.

Do glaucoma treatments work while I sleep?

Not all of them equally. Prostaglandin eye drops (such as latanoprost) and selective laser trabeculoplasty (SLT) lower pressure around the clock, including overnight. Some other drop classes, such as beta-blockers like timolol, work mainly during the day and have a weaker effect at night. This difference is one reason a glaucoma specialist chooses specific medications, and often considers laser treatment, based on each patient’s pressure pattern.

Told your pressure is “fine” but never had a full glaucoma evaluation? Our board-certified glaucoma specialists look at the whole 24-hour picture: pressure patterns, corneal thickness, OCT, and visual fields.