Since Flammer’s early work, glaucoma has lived in the tension between 2 competing theories: mechanical damage and vascular compromise.¹ On one hand, elevated IOP deforms the lamina cribrosa and injures axons.² On the other, insufficient perfusion leaves the optic nerve vulnerable, even when IOP is in a “normal” range.^1,2

We’ve all been trained to manage pressure inside the eye. The challenge is that the pressure outside the eye—blood pressure—is less straightforward.

The American Optometric Association and American Academy of Ophthalmology recognize the paradox: Both hypertension and hypotension can increase glaucoma risk.^3,4 Low blood pressure, particularly low diastolic pressure, has been associated consistently with both conversion and progression.⁴ 

Perfusion dips in the early hours of the morning may also give us some insight, which the Maracaibo Aging Study helped clarify. Average 24-hour BP wasn’t really the issue; it was nocturnal dipping.⁵ Patients with drops in nighttime BP of more than 20% had significantly higher risk of glaucomatous damage.⁵ In other words, a patient with “normal” office BP may still be underperfusing their optic nerve every night.

Hypertension complicates things further. Although higher BP may initially support perfusion, chronic hypertension leads to vascular remodeling, impaired autoregulation, and ultimately reduced effective blood flow.⁴ What starts as protective most likely becomes harmful over time.

Shifting our attention toward patterns in BP variability may be helpful. A 2025 study by Pham et al showed that blood pressure variability is a major driver of progression.⁶ Patients with higher mean BP and greater fluctuation experienced faster visual field mean deviation loss.⁶ The optic nerve may struggle with BP extremes and instability.

Think of autoregulation as the optic nerve’s shock absorber. It can sometimes handle pressure, but constant swings may be more challenging.

What Do We Do With This Information Clinically?

First, consider nocturnal hypotension in patients whose glaucoma is progressing despite good IOP control. Ambulatory blood pressure monitoring may sometimes uncover extreme dippers who would otherwise go undetected.⁶

Second, rely less on single BP readings and instead look for patterns. Be especially aware of consistent low diastolic pressures and wide variability between visits.⁶

Third, consider reducing topical beta blockers or confine them to morning doses only. Stay away from beta blockers in normal tension glaucoma patients. When prescribing combination drops that include beta blockers, consider making the evening dose no later than 5 or 6 PM.

Finally, collaborate. When you identify extreme dipping or high variability, a conversation with the patient’s PCP about antihypertensive timing can be meaningful. In some cases, shifting medication away from bedtime may help stabilize nocturnal perfusion.

We’re good at lowering IOP. We would be wise to remember that glaucoma is both a pressure problem and a perfusion problem. Paying attention to the other pressure may give us important insight into this disease.OM

References

1. Flammer J, Orgül S, Costa VP, et al. The impact of ocular blood flow in glaucoma. Prog Retin Eye Res. 2002;21(4):359–393. doi:10.1016/s1350-9462(02)00008-3
2. Ahmad SS. The mechanical theory of glaucoma in terms of prelaminar, laminar, and postlaminar factors. Taiwan J Ophthalmol. 2024;14(3):376–386. doi: 10.4103/tjo.TJO-D-23-00103
3. AOA Evidence-Based Optometry Guideline Development Group. Care of the patient with primary open-angle glaucoma. American Optometric Association. October 5, 2024. Accessed May 27, 2026. https://www.aoa.org/documents/EBO/GLAUCOMA/FINAL_EBO_Glaucoma_Guildline_digital_10_28_24.pdf
4. Gedde SJ, Vinod K, Wright MM, et al. Primary open-angle glaucoma preferred practice pattern. Ophthalmology. 2021;128(1):71–150. doi:10.1016/j.ophtha.2020.10.022
5. Melgarejo JD, Lee JH, Petitto M, et al. Glaucomatous optic neuropathy associated with nocturnal dip in blood pressure: findings from the Maracaibo Aging Study. Ophthalmology. 2018;125(6):807-814. doi:10.1016/j.ophtha.2017.11.029
6. Pham VQ, Nishida T, Moghimi S, et al. Long-term blood pressure variability and visual field progression in glaucoma. JAMA Ophthalmol. 2025;143(1):25-32. doi: 10.1001/jamaophthal

Mike Cymbor, OD, FAAO is director of the Glaucoma Institute of State College and the lead OD at Nittany Eye Associates in State College, Pennsylvania.