One eye is swollen, painful, red; there’s a rainbow halo around lights; plus headache, nausea, and vomiting — so an emergency eye visit is needed that same day.

This is an acute glaucoma attack. Fluid can’t drain from the eye, so pressure spikes quickly. The longer it goes untreated, the more damage occurs to the optic nerve, and that damage is permanent. During Wuhan’s lockdown, patients waited an average of 241 hours before getting treatment; 21.87% ended up blind. In the same period the year after the lockdown, the average wait time dropped to 121 hours, and only 7.84% became blind. A total of 76 days of lockdown were covered in this study.

No cost at all. An emergency eye exam includes measuring intraocular pressure and checking the anterior chamber, which takes up half a day.

An eye hospital in Wuhan compared two groups of patients with acute primary angle-closure glaucoma. In 2020, during the lockdown, 54 patients with 64 affected eyes received care; the following year, 46 patients with 51 affected eyes were treated. Both groups had similar demographic profiles. From symptom onset to treatment, the lockdown group waited 241.84±211.95 hours versus 121.53±96.12 hours for the control group (P=0.001). Their intraocular pressure at diagnosis was 52.63±12.45 mmHg versus 45.16±9.79 mmHg (P=0.001). Blindness rates were 21.87% versus 7.84%. Glaucomatous optic nerve damage was found in 20/64 eyes (31.25%) versus 7/51 eyes (13.73%) (P=0.03). A South Korean hospital reviewed 50 eyes that had experienced one acute attack and later had their lenses removed; a year later, 25 of those eyes (50%) showed varying degrees of visual field loss. The longer the time between symptom onset and pressure reduction, the higher the chance of lasting damage (P=0.005). Another prospective study had 43 people with shallow anterior chambers lie face-down in a dark room for one hour; intraocular pressure rose significantly in both eyes (P<0.01). The dominant eye saw a median increase of 3.60 mmHg, while the other eye rose 2.70 mmHg (P<0.05).

There are two main reasons this is graded B. First, the Wuhan comparison relied on reviewing old medical records, and the lockdown itself introduced other differences that can’t be separated from the effect of delayed treatment. Second, the South Korean study involved only 50 eyes and was retrospective. This does not mean screen time causes glaucoma; in the dark, pupils dilate, and prolonged head-down posture pushes the lens forward, especially in people with naturally shallow anterior chambers. Those at highest risk are over 50, farsighted, or with a family history of angle-closure glaucoma. Young people who game all night are unlikely to develop this condition. Common misdiagnoses during an attack include gastroenteritis, migraine, or high blood pressure, since headache and vomiting are more noticeable than eye symptoms. Sudden, painless vision loss in one eye is a separate issue — see item 5 (sudden blackout in one eye). Whether blue-light blocking glasses help is discussed in section 6, item 16 (blue-light blocking glasses).

Zhou L, Wu S, Wang Y, Bao X, Peng T, Luo W, Ortega-Usobiaga J (2022). Clinical presentation of acute primary angle closure during the COVID-19 epidemic lockdown. Frontiers in Medicine, 9, 1078237. https://doi.org/10.3389/fmed.2022.1078237 ; Sung MS, Kim HJ, Park SW (2023). Predictors of long-term visual field outcome after an episode of acute primary angle closure. Clinical & Experimental Ophthalmology, 51(4), 291-299. https://doi.org/10.1111/ceo.14206 ; Wang J, Wang J, Ng TK, Huang C (2025). Asymmetric intraocular pressure changes in dominant and contralateral eyes: the dark room prone provocative test. Seminars in Ophthalmology, 40(4), 325-331. https://doi.org/10.1080/08820538.2024.2443972 ; NHS. Glaucoma：「Sometimes glaucoma can develop suddenly and cause symptoms such as: intense eye pain, a red eye, tenderness around the eyes, seeing rainbow-coloured circles around bright lights, blurred vision, feeling sick (nausea) and being sick, a headache」「This happens when the fluid in your eye cannot drain as it should」. https://www.nhs.uk/conditions/glaucoma/ ; Lin SF, Xiao H, Chen LM, et al. (2022). [Clinical features of young inpatients with angle-closure glaucoma]. 中华眼科杂志, 58(1), 28-34. https://doi.org/10.3760/cma.j.cn112142-20210301-00104