Yes, diabetes is a meaningful risk factor for glaucoma. People with diabetes are about 36% more likely to develop glaucoma than people without it, based on a meta-analysis of seven prospective cohort studies. The connection runs through several biological pathways, from subtle changes in how fluid drains from the eye to a more severe form of glaucoma triggered by advanced diabetic eye disease.
How Diabetes Raises Glaucoma Risk
Glaucoma damages the optic nerve, usually because pressure inside the eye climbs too high. In a healthy eye, fluid (called aqueous humor) flows in and drains out through a tiny mesh-like tissue near the iris. Diabetes disrupts this drainage system in ways that can quietly raise eye pressure over years.
When blood sugar stays elevated, the body produces more of a protein called fibronectin inside the eye’s drainage tissue. This protein builds up and physically clogs the outflow channels, making it harder for fluid to leave the eye. At the same time, high glucose reduces the activity of enzymes that normally clear away this buildup, so the blockage compounds over time. The result is a slow, steady rise in intraocular pressure. On average, diabetic patients see roughly a 0.1 mmHg increase in eye pressure for every 10 mg/dL rise in fasting blood sugar. That sounds tiny, but it accumulates.
Diabetes also damages the small blood vessels that supply the optic nerve and retina. This microvascular injury weakens the nerve’s ability to regulate its own blood flow, making it more vulnerable to pressure-related damage. There’s even evidence that diabetes changes the structure of the connective tissue at the back of the eye where the optic nerve exits, further increasing susceptibility to glaucoma through purely mechanical changes.
Neovascular Glaucoma: A More Severe Form
Beyond the gradual pressure increases described above, diabetes can trigger a distinct and more aggressive type called neovascular glaucoma. This form accounts for a small share of all glaucoma cases, but diabetes is responsible for more than 30% of them.
The chain of events starts with diabetic retinopathy, the condition where high blood sugar damages retinal blood vessels. As those vessels deteriorate, patches of the retina become starved for oxygen. The eye responds by flooding the area with growth signals that stimulate new blood vessel formation. These new vessels are fragile and grow in the wrong places, including across the iris and into the drainage angle at the front of the eye. Fibrous membranes form alongside them, physically blocking the eye’s drainage channels and causing a sharp, dramatic spike in eye pressure.
Among all people with diabetes, about 2.1% develop neovascular glaucoma. But among those who have progressed to proliferative diabetic retinopathy (the advanced stage with abnormal vessel growth), the rate jumps to 21.3%. After certain eye surgeries in diabetic patients with multiple risk factors, the incidence can reach as high as 80%. This is why managing diabetic retinopathy early matters so much for long-term eye health.
Does Better Blood Sugar Control Protect Against Glaucoma?
This is where the evidence gets nuanced. Controlling blood sugar clearly reduces the risk of developing diabetic retinopathy in the first place, which in turn lowers the chance of neovascular glaucoma. But for the more common type, open-angle glaucoma, the picture is less straightforward.
A study published in Investigative Ophthalmology & Visual Science tracked glaucoma patients and suspects over time, measuring their HbA1c (a marker of average blood sugar over two to three months) alongside the rate of vision loss. After adjusting for other factors, there was no statistically significant link between HbA1c levels and how fast glaucoma progressed. Peak HbA1c values and blood sugar fluctuations also showed no meaningful association with worsening visual field loss. In other words, once open-angle glaucoma has developed, tighter blood sugar control alone doesn’t appear to slow it down. The damage mechanisms at that point are largely about eye pressure and optic nerve vulnerability, which need their own targeted treatment.
Metformin and Glaucoma Protection
One of the more interesting findings in recent years involves metformin, the most commonly prescribed medication for type 2 diabetes. People taking metformin show a 19% lower risk of developing glaucoma compared to diabetic patients not on the drug, even after accounting for blood sugar control, eye pressure, diabetes duration, and other variables. A meta-analysis of multiple cohort studies confirmed this protective effect, with a pooled risk reduction of 19%.
What makes this particularly compelling is that the benefit appears to go beyond simply lowering blood sugar. When researchers adjusted specifically for eye pressure measurements in a subgroup of nearly 4,700 people, metformin users still had roughly half the glaucoma risk. And a genetic analysis modeling the effects of metformin’s drug targets found a 34% lower glaucoma risk per unit of blood sugar reduction, suggesting the drug may protect the optic nerve through additional pathways like reducing inflammation or oxidative stress.
This doesn’t mean metformin is a glaucoma treatment. But for people with type 2 diabetes who are already taking it, there may be an eye health benefit that wasn’t part of the original prescription.
What This Means for Screening
Because glaucoma develops slowly and painlessly in most cases, the 36% increased risk in diabetes makes regular comprehensive eye exams especially important. Most people with diabetes already get annual dilated eye exams to check for retinopathy. These same exams can detect elevated eye pressure and early optic nerve changes before any vision loss occurs.
The two conditions share a timeline problem: both diabetes and open-angle glaucoma can go undiagnosed for years. An estimated half of people with glaucoma don’t know they have it, and a significant portion of people with type 2 diabetes are also undiagnosed. If you’ve been told you have diabetes or prediabetes, a dilated eye exam does double duty, screening for both retinopathy and the early signs of glaucoma in a single visit. Once identified, glaucoma is manageable with pressure-lowering drops, laser procedures, or minor surgery, but the damage already done to the optic nerve at the time of diagnosis cannot be reversed.