What are the early signs of glaucoma? For the common type, there usually aren't any

The most useful thing to know about the early signs of glaucoma is that, for the common form, there usually are none. That is precisely what makes it dangerous — and why the disease is found through eye exams rather than symptoms.

Why "early signs" is the wrong question

Open-angle glaucoma is the most common type in the United States, and it is what most people mean when they say glaucoma [s1]. At first, in the National Eye Institute's description, it does not usually have any symptoms — which is why half of people with glaucoma do not even know they have it [s1]. Over time, vision is lost slowly, usually starting with side (peripheral) vision, especially the part closest to the nose [s1]. Because the loss is so gradual, many people cannot tell their vision is changing until they can no longer see things off to the side, and without treatment glaucoma can eventually cause blindness [s1].

MedlinePlus puts the same point more bluntly: with open-angle glaucoma, most people have no symptoms, and once you are aware of vision loss, the damage is already severe [s3]. Slow loss of side vision — sometimes called tunnel vision — is the main pattern, and advanced disease can lead to blindness [s3]. Lost vision is not recovered, so the entire value of an early diagnosis is in stopping further loss.

Who should get checked, and how

Because there is nothing to feel, risk factors decide who needs looking at. The NEI lists higher risk for people over 60, especially those who are Hispanic or Latino; African Americans over 40; and anyone with a family history of glaucoma [s1]. For people at higher risk, it recommends a comprehensive dilated eye exam every one to two years [s1]. The exam is simple and painless: drops widen the pupil, and it includes a visual field test to check side vision [s1].

The NEI is also candid about prevention. There is no way to prevent glaucoma, it states — which is exactly why exams matter, so that you and your doctor can find it before it affects your vision [s1].

The one kind that does cause sudden symptoms

There is an important exception. Angle-closure glaucoma can cause sudden symptoms: intense eye pain, an upset stomach or nausea, a red eye and blurry vision [s1]. This is a medical emergency — the NEI says to go to a doctor or an emergency room now if these appear [s1], and MedlinePlus similarly advises immediate help for severe eye pain or a sudden loss of vision, which may be signs of closed-angle glaucoma [s3].

What treatment actually achieves

Scientists are not sure what causes the common forms of glaucoma, but many people who have it have high pressure inside the eye, and treatments that lower that pressure help to slow the disease [s1]. The strongest evidence that lowering pressure preserves vision, rather than just numbers, comes from the United Kingdom Glaucoma Treatment Study.

UKGTS was a randomised, triple-masked, placebo-controlled trial — a design earlier glaucoma trials had not used for this question. It enrolled 516 patients with newly diagnosed open-angle glaucoma at ten UK centres, assigning 258 to latanoprost 0.005% eye drops and 258 to placebo drops, from identical bottles [s2]. Baseline intraocular pressure was 19.6 mm Hg (SD 4.6) in the latanoprost group and 20.1 mm Hg (4.8) in controls [s2]. At 24 months, mean pressure had fallen by 3.8 mm Hg in the 231 latanoprost patients assessed, against 0.9 mm Hg in the 230 placebo patients [s2].

The result that mattered was visual function. Preservation of the visual field was significantly longer in the latanoprost group than in the placebo group, with an adjusted hazard ratio of 0.44 (95% CI, 0.28–0.69; p=0.0003) [s2]. There were 18 serious adverse events, none attributable to the study drug [s2]. In short, drops that lowered pressure roughly halved the rate at which the visual field deteriorated over two years — direct evidence that treating the pressure protects sight.

The practical takeaway

Waiting to notice a symptom is, for the common glaucoma, waiting too long. The disease is caught by routine dilated eye exams, and the payoff of catching it is real: pressure-lowering treatment slows the loss of vision. This article is informational and is not medical advice; how often you should be examined, and whether you need treatment, are decisions for an eye-care professional. Sudden severe eye pain, nausea and a red eye are a reason to seek emergency care immediately.

Sources

• Glaucoma — National Eye Institute, 2026-08-19
• Latanoprost for open-angle glaucoma (UKGTS): a randomised, multicentre, placebo-controlled trial — The Lancet, 2015-04-01
• Glaucoma (MedlinePlus Medical Encyclopedia) — U.S. National Library of Medicine (MedlinePlus), 2024-07-09