Most forms of glaucoma are silent in their early stages, which is why a routine eye exam, not symptoms, is the most reliable way to detect it. The earliest and most common sign is a slow reduction in peripheral (side) vision, and it often goes unnoticed for a long time because the brain compensates for the missing information.
As the disease progresses, peripheral loss can narrow to the point where a person feels as though they are looking through a tunnel. Blurred vision and colored halos or rings around lights deserve prompt evaluation. Sudden severe eye pain, intense headache with eye discomfort, rapid blurring, redness, or nausea and vomiting alongside eye symptoms can signal an acute angle-closure attack, a true eye emergency that requires same-day treatment.