Glaucoma’s Hidden Nighttime Ambush

Your eye doctor may be checking the wrong number — and it could be costing you your vision.

Quick Take

Glaucoma research is challenging the long-held belief that average eye pressure is the main driver of vision loss.
Pressure spikes and drops throughout the day may damage the optic nerve more than a steady, elevated pressure ever could.
Two landmark studies — the Advanced Glaucoma Intervention Study and the UK Glaucoma Treatment Study — found pressure swings to be a stronger predictor of vision loss than average pressure alone.
Up to 75% of glaucoma patients hit their peak eye pressure outside of normal office hours, meaning most doctors never see the most dangerous readings.

The Number Your Eye Doctor Checks May Not Be the Right One

For decades, glaucoma care has revolved around one measurement: your intraocular pressure (IOP), meaning the pressure inside your eye, taken during a brief office visit. Doctors set a target number. They check it a few times a year. If it looks acceptable, treatment seems to be working. It is a clean, simple system. The problem is that glaucoma does not always follow clean, simple rules. A growing body of research suggests that the swings in pressure — not just the average — may be what is actually destroying the optic nerve.

Glaucoma as a Repetitive Strain Injury

Mayo Clinic ophthalmologist Dr. Arthur Sit has proposed a striking way to think about this. He compares glaucoma to a repetitive strain injury — like the kind a carpenter gets from swinging a hammer thousands of times. No single swing breaks the wrist. But the repeated stress-and-release cycle eventually exhausts the tissue’s ability to repair itself. The optic nerve, Sit argues, works the same way. Rapid, repeated pressure spikes may wear down the nerve’s repair mechanisms faster than a high but stable pressure would.^[5]

The Advanced Glaucoma Intervention Study, one of the most important trials in glaucoma history, backed this idea with hard data. It found that pressure fluctuation was an independent and powerful predictor of vision loss — especially in patients whose average pressure was already low. That last part is critical. These were patients whose doctors would have looked at the chart and said everything was under control. Their average pressure was fine. Their vision was still deteriorating.^[2]

The Evidence Is Strong, But the Debate Is Real

Not every major trial agrees. The Early Manifest Glaucoma Treatment trial found that average pressure, not fluctuation, was the primary driver of progression. The Ocular Hypertension Treatment Study reached a similar conclusion. These are serious, well-designed studies, and they cannot be dismissed. But they also did not measure pressure the way the newer research does — continuously, across a full 24-hour cycle, capturing the peaks that happen at night or in the early morning when no one is watching.^[11]

A 2024 peer-reviewed analysis found that glaucoma patients show significantly greater pressure swings than healthy people, even when their average pressure falls within the normal range. Healthy eyes typically stay within a 5 mmHg window over a full day. Glaucoma patients blow past that regularly. The Los Angeles Latino Eye Study found that among patients with lower pressures, it was the maximum reading, the range, and the standard deviation that predicted glaucoma risk — not the mean.^[1]^[4]

The Measurement Problem Nobody Talks About

Here is where the science hits a wall. Studies show that up to 75% of glaucoma patients reach their peak pressure outside of office hours. Doctors are measuring pressure during the day. The damage may be happening at night. Dr. Sit acknowledges this directly — current clinical protocols capture a single snapshot, and that snapshot may be missing the most dangerous part of the story. This is not a small gap. It is potentially the difference between catching a problem and watching it quietly get worse.^[2]^[7]

Dr. Sit’s own research using ultrasound vibroelastography adds another layer. He found that patients with normal-tension glaucoma — a form where vision loss occurs despite normal average pressures — have stiffer scleral tissue and optic nerve heads than healthy individuals. Stiffer tissue is less forgiving. Even a modest pressure swing in a stiff eye may cause more mechanical damage than a larger swing in a more flexible one. This could help explain why some patients go blind despite “normal” pressures for years.^[5]

What Has to Change Before This Reshapes Treatment

The medical establishment moves slowly, and for good reason. Association is not causation. The fluctuation hypothesis still lacks the definitive controlled trial that would prove pressure swings cause optic nerve damage rather than simply accompany it. Less than half of glaucoma patients take their prescribed eye drops as directed, which makes it nearly impossible to run clean clinical tests on any treatment strategy. And clinical guidelines still define target pressure as a single number, not a fluctuation range.^[6]

But the tools to close that gap are arriving. Food and Drug Administration-approved contact lens sensors and implantable devices can now track eye pressure continuously for 24 hours. That data, collected at scale, could finally answer whether the spikes matter as much as the evidence suggests. If they do, the standard glaucoma office visit — and the single pressure reading it produces — may need a serious rethink.