Low-pressure glaucoma, also called normal-tension glaucoma (NTG), is a form of glaucoma in which the optic nerve sustains progressive damage even though eye pressure stays within the range considered normal, typically at or below 21 mmHg. It accounts for a substantial share of all open-angle glaucoma cases and is especially common in East Asian populations. Because the eye pressure readings look reassuring, the condition often goes undetected until noticeable vision loss has already occurred. Treatment still revolves around lowering eye pressure further, but managing the systemic and vascular factors that contribute to the damage turns out to be just as important.
How It Differs from Typical High-Pressure Glaucoma
In the more familiar form of open-angle glaucoma, elevated eye pressure gradually crushes the optic nerve fibers at the back of the eye. The logic feels straightforward: high pressure causes damage, so bring the pressure down. Low-pressure glaucoma breaks that logic. The eye pressure is already in a range most clinicians would call safe, yet the optic nerve deteriorates anyway. And the pattern of damage tends to be different. Visual field defects in low-pressure glaucoma are often more localized and deeper than the broad, shallow losses seen in typical high-pressure cases, and the disease may progress more quickly.
1National Journal glaucoma. Features of medical and surgical treatment of normal-tension glaucomaThere is an ongoing debate about whether low-pressure glaucoma is truly a separate disease or just the lower end of the same spectrum as primary open-angle glaucoma. The answer likely lies somewhere in between. The two conditions share overlapping genetics and structural changes, but low-pressure glaucoma appears to involve more vascular and mechanical factors beyond eye pressure alone.
Why the Optic Nerve Gets Damaged Without High Pressure
If the pressure inside the eye is not elevated, something else must be making the optic nerve vulnerable. Researchers have identified several mechanisms, and most patients probably have more than one at work simultaneously.
Blood Flow Problems
The optic nerve needs a steady supply of blood, and anything that disrupts that supply can cause damage. One of the biggest culprits is what happens at night. When you sleep, your blood pressure naturally dips. In some people, it dips too far. A study tracking 48-hour blood pressure patterns found that the total time a person’s blood pressure during sleep dropped more than 10 mmHg below their daytime average was a significant predictor of glaucoma progression.
2PubMed Central. Nocturnal Systemic Hypotension Increases the Risk of Glaucoma ProgressionWhat matters is not just average blood pressure but how much it fluctuates. Long-term swings in blood pressure and in ocular perfusion pressure (the difference between blood pressure and eye pressure, which determines how much blood reaches the eye) are tied to visual field worsening in normal-tension glaucoma.
3PubMed Central. Associations of long-term fluctuation in blood pressure and ocular perfusion pressure with visual field progression in normal-tension glaucomaThe nighttime dip in blood pressure also causes wide swings in ocular perfusion pressure over 24 hours, and those swings themselves are considered a risk factor for developing the disease.
4PubMed. Effect of nocturnal blood pressure reduction on circadian fluctuation of mean ocular perfusion pressure: a risk factor for normal tension glaucomaBeyond blood pressure patterns, a range of systemic vascular conditions show up far more often in people with low-pressure glaucoma than in the general population. A large study found significantly higher rates of diabetes, peripheral vascular disease, migraine, anemia, Raynaud syndrome, and both systemic hypertension and systemic hypotension among these patients. Low systemic blood pressure carried the strongest association, with roughly four times the odds compared to controls.
5PubMed Central. Multiple Systemic Vascular Risk Factors Are Associated With Low-Tension GlaucomaThe Pressure Across the Optic Nerve
The optic nerve passes through a sieve-like structure called the lamina cribrosa as it exits the eye. On one side of this structure is the eye’s internal pressure; on the other is the pressure of the cerebrospinal fluid that bathes the brain and optic nerve. What matters for the nerve is the pressure difference across this barrier. In people with low-pressure glaucoma, cerebrospinal fluid pressure tends to be lower than normal, which creates a steeper pressure gradient across the lamina cribrosa even when eye pressure is fine. The optic nerve essentially gets squeezed from the front while lacking sufficient back-pressure to counterbalance.
6PubMed Central. Cerebrospinal fluid pressure and glaucomaA Thinner, More Vulnerable Lamina Cribrosa
Imaging studies using enhanced depth optical coherence tomography have found that the lamina cribrosa is thinner in people with normal-tension glaucoma compared to healthy controls.
7PubMed. Enhanced depth imaging detects lamina cribrosa thickness differences in normal tension glaucoma and primary open-angle glaucomaA thinner lamina may be structurally weaker and more susceptible to deformation under even modest pressure. The lamina also tends to bow backward more than normal, though this displacement is generally less severe than what is seen in high-pressure glaucoma.
8PubMed. Posterior displacement of the lamina cribrosa in normal-tension and high-tension glaucomaWho Is Most at Risk
Low-pressure glaucoma is more prevalent in Asia than in Western countries, a fact that has driven a large share of the research into the condition.
9PubMed Central. Normal tension glaucoma in Asia: Epidemiology, pathogenesis, diagnosis, and managementIn Japan, for instance, normal-tension glaucoma makes up the majority of all open-angle glaucoma cases. Family history is a meaningful risk factor. About 2% of normal-tension glaucoma cases are driven primarily by mutations in single genes, including optineurin (OPTN), TANK binding kinase 1 (TBK1), and myocilin (MYOC).
10PubMed. Familial normal tension glaucoma geneticsA specific variant in the optineurin gene, Met98Lys, has been found at roughly three to four times the frequency in Japanese patients with normal-tension glaucoma compared to controls.
11PubMed. Molecular genetic analysis of optineurin gene for primary open-angle and normal tension glaucoma in the Japanese populationTwo percent may sound small, but it matters because those mutations tend to cause particularly aggressive disease. For the remaining cases, genetics likely contributes through many small-effect variants interacting with vascular and structural risk factors rather than through any single identifiable gene.
How It Gets Diagnosed
Diagnosis is tricky precisely because the pressure looks normal on a standard eye exam. A single pressure reading in the office is not enough. Clinicians often want multiple readings taken at different times of day, since eye pressure fluctuates throughout a 24-hour cycle and may peak at times the patient is not sitting in the exam chair.
The key diagnostic findings are a characteristic pattern of optic nerve thinning and visual field loss in the absence of elevated eye pressure. Optical coherence tomography measures the thickness of the retinal nerve fiber layer. One clinical approach classifies eyes with an average nerve fiber layer thickness below 80 micrometers as possible normal-tension glaucoma and refers them for visual field testing. Corneal hysteresis, a measure of the cornea’s biomechanical properties, has also shown value in early diagnosis and may help distinguish genuinely normal eyes from eyes that merely appear to have normal pressure because of how their cornea behaves.
12PubMed Central. The role of corneal hysteresis during the evaluation of patients with possible normal-tension glaucomaPart of the diagnostic workup also involves ruling out other causes of optic nerve damage that mimic glaucoma, including compressive lesions, past episodes of low blood pressure, or a history of blood loss. Brain imaging is sometimes ordered when the clinical picture does not quite fit.
The 30% Target and Why It Works
Even though eye pressure is already within the normal range, lowering it further is the one intervention proven to slow progression. The landmark Collaborative Normal-Tension Glaucoma Study randomized patients to either no treatment or a 30% reduction in eye pressure from baseline. The treated group had significantly less visual field progression, establishing the 30% reduction as a widely used clinical target.
13PubMed. The effectiveness of intraocular pressure reduction in the treatment of normal-tension glaucoma 1450 Studies Every Ophthalmologist Should Know. Intraocular Pressure Reduction in the Treatment of Normal-Tension Glaucoma
For a patient whose starting pressure is, say, 16 mmHg, a 30% reduction means getting it down to around 11. That is not easy when you are already starting from a relatively low number, and it explains why treatment for this condition sometimes feels like a tighter balancing act than for high-pressure glaucoma.
Eye Drops and Neuroprotection
First-line treatment usually involves prescription eye drops. A head-to-head trial compared brimonidine 0.2% against timolol 0.5% over two years. Visual field progression was reduced by about 39% with brimonidine versus about 9% with timolol, a striking difference that pointed to benefits beyond simple pressure lowering.
15Preventing Chronic Disease (CDC). Low-Tension Glaucoma: An Oxymoron in OphthalmologyWhy the gap? Brimonidine may offer some neuroprotective effects on top of its pressure-lowering action. Laboratory and early clinical evidence suggests it protects retinal ganglion cells through mechanisms independent of pressure reduction, and studies have shown improvements in contrast sensitivity in brimonidine-treated eyes that cannot be explained by pressure changes alone.
16PubMed Central. Clinical efficacy and neuroprotective effects of brimonidine in the management of glaucoma and ocular hypertensionProstaglandin analogs like latanoprost are also commonly used and are effective at lowering pressure. A study comparing latanoprost and brimonidine in normal-tension glaucoma found that both improved pulsatile ocular blood flow, with latanoprost showing a larger increase of about 23% compared to about 10% for brimonidine. However, after adjusting for the pressure-lowering effect itself, neither drug significantly increased blood flow, suggesting the blood flow improvement was largely a downstream consequence of lower eye pressure rather than a separate vascular benefit.
17PubMed Central. Effect of latanoprost 0.005% and brimonidine tartrate 0.2% on pulsatile ocular blood flow in normal tension glaucomaLaser Trabeculoplasty
Selective laser trabeculoplasty (SLT) works by stimulating the eye’s drainage tissue to allow fluid to exit more efficiently, reducing pressure. It has increasingly been studied as a treatment option for normal-tension glaucoma, either as a first-line approach or as an add-on when drops are not enough.
A multicentre cohort study found that SLT reduced pressure by about 17% when used as a first-line treatment and about 13% as a second-line option, with both reductions maintained at 12 months.
18PubMed Central. Efficacy and safety of first-line or second-line selective laser trabeculoplasty for normal-tension glaucoma: a multicentre cohort studyAnother study found that a single SLT session achieved an additional 15% pressure reduction while allowing patients to use about 27% less medication at one year.
19PubMed Central. Efficacy of selective laser trabeculoplasty for normal tension glaucoma: 1 year resultsThe catch is durability. Longer follow-up data from a study in Chinese patients showed that the success rate declined from about 41% at six months to roughly 18% at two years.
20PubMed. Intraocular pressure-lowering effects of selective laser trabeculoplasty for normal tension glaucoma patients in ChineseSLT can be repeated, which is one of its advantages over some other procedures, but it is probably best thought of as a helpful tool for reducing the medication burden rather than a permanent fix.
When Surgery Becomes Necessary
If drops and laser are not enough to reach the target pressure or if the disease keeps progressing, filtration surgery becomes an option. Trabeculectomy, the most established glaucoma surgery, creates a new drainage channel for fluid to leave the eye. When performed with mitomycin C (an agent that prevents the new channel from scarring shut), it can achieve very low pressures. One study of trabeculectomy with mitomycin C for normal-tension glaucoma reported final pressures between 5 and 12 mmHg in 87% of eyes, with a mean pressure of about 8 mmHg.
21PubMed. Trabeculectomy with mitomycin C for normal-tension glaucomaThose are impressively low numbers, but surgery at these levels carries real risks, including hypotony (pressure that is too low), cataract formation, and infection. The decision to operate is usually reserved for cases where the disease is clearly progressing despite maximum medical and laser therapy, or where the patient cannot tolerate the drops.
Minimally invasive glaucoma surgeries (MIGS) have gained traction in recent years as a lower-risk alternative. They generally produce a more modest pressure reduction than trabeculectomy but come with fewer complications. Their role in normal-tension glaucoma is still being defined, since the pressure drops they achieve may not always reach the aggressive targets these patients need.
Managing Blood Pressure and Nighttime Dips
Because blood supply to the optic nerve matters so much in this disease, managing systemic blood pressure is part of the picture. Paradoxically, aggressively treating high blood pressure can sometimes hurt the optic nerve if it drives nighttime blood pressure too low. A study of patients with both hypertension and open-angle glaucoma found that those who took their blood pressure medication in the evening had significantly lower nighttime perfusion pressure, greater visual field loss, and worse optic nerve function compared to those who dosed only in the morning.
22PubMed. Effects of the time of antihypertensive drugs administration on the stage of primary open-angle glaucoma in patients with arterial hypertensionThis does not mean you should change your blood pressure medication schedule without talking to your doctor. But it does mean the conversation is worth having. If you have normal-tension glaucoma and take evening antihypertensives, your eye doctor and cardiologist or primary care physician should be coordinating. The goal is to control systemic blood pressure without starving the optic nerve overnight.
Sleep Apnea and Low-Pressure Glaucoma
Obstructive sleep apnea has emerged as a significant associated condition. A study comparing normal-tension glaucoma patients with visual field loss to controls found that those with field loss had significantly more severe sleep apnea, and over 90% of the group with visual field damage had at least moderate obstructive sleep apnea.
23PubMed Central. Normal tension glaucoma in obstructive sleep apnea syndrome: A structural and functional studyThe connection likely runs through both vascular and mechanical pathways. Sleep apnea causes repeated episodes of low oxygen and swings in blood pressure during the night, exactly the kind of perfusion instability that the optic nerve handles poorly. CPAP therapy, the standard treatment for sleep apnea, improves oxygenation but may have its own effect on the eye. One study found that CPAP use was associated with a modest increase in eye pressure over 12 months, though visual field measures were stable or slightly improved.
24PubMed Central. Long-term Effect of Continuous Positive Air Pressure Therapy on Intraocular Pressure in Patients with Primary Open-angle Glaucoma with Obstructive Sleep ApneaFor someone with normal-tension glaucoma and untreated sleep apnea, addressing the sleep disorder is likely beneficial overall, but eye pressure should be monitored once CPAP is initiated.
Disc Hemorrhages as a Warning Sign
Small, flame-shaped bleeds on or near the optic disc, called disc hemorrhages, show up more often in normal-tension glaucoma than in high-pressure forms of the disease. They tend to appear on the temporal side of the disc, especially the lower-temporal region, and are generally considered a sign that the disease is active and may be progressing.
25PubMed Central. Disc Hemorrhages in Patients with both Normal Tension Glaucoma and Branch Retinal Vein Occlusion in Different EyesA disc hemorrhage is fleeting and easy to miss. It may only be visible during one exam visit and gone by the next. But its presence signals localized vascular fragility at the optic nerve head and often predicts a worsening of the visual field in the corresponding area. When a disc hemorrhage is spotted, clinicians may decide to intensify treatment or shorten the monitoring interval, even if pressure measurements look acceptable.
Artificial Intelligence in Progression Prediction
One of the challenges with normal-tension glaucoma is predicting which patients will get worse and which will remain stable. A recent AI model trained on clinical data from patients with myopic normal-tension glaucoma achieved an area under the curve of 0.83 for predicting visual field progression. The most important predictive factors were baseline visual field severity, age, eye length, starting eye pressure, and the visual field index. Patients flagged by the model as high-risk had observed progression rates above 80%.
26PubMed Central. SMOTE-Enhanced Explainable Artificial Intelligence Model for Predicting Visual Field Progression in Myopic Normal Tension GlaucomaThis kind of tool is not yet in routine clinical use, but it reflects where the field is heading. Better risk stratification could mean that patients at genuinely high risk of progression get aggressive treatment early, while lower-risk patients are spared the side effects and cost of unnecessary interventions. For a condition where the starting pressure is already “normal” and every additional mmHg of reduction becomes harder to achieve, knowing whom to treat aggressively matters enormously.