Lying in bed with the lights off, the smartphone screen the only source of brightness. This habit has become a familiar routine for ending the day, but ophthalmologists warn it is a risk factor that can trigger acute glaucoma.
According to national disease statistics of public interest from the Health Insurance Review and Assessment Service released Friday, the number of patients who visited hospitals for glaucoma rose from 967,554 in 2021 to 1,223,254 in 2025, an increase of about 26 percent over five years.
Once considered a condition of the middle-aged and elderly, glaucoma is now breaking age boundaries. Patients in their 20s and 30s increased from 104,348 to 118,106 over the same period, a rise of about 13,700 patients, or roughly 13 percent.
Looking at a smartphone for a long time in a dark room causes a conflict inside the eye between the pupil's response and the structure that drains aqueous humor.
When entering a dark environment, the eye widens the pupil to take in more light. When the eye focuses on a nearby screen in this state, the lens thickens and shifts forward, which can narrow or block the anterior chamber angle, the passage through which aqueous humor drains. Aqueous humor is the fluid that keeps the pressure inside the eye constant, and if drainage is not smooth, intraocular pressure rises.
A domestic study confirmed this phenomenon in numbers. In research conducted by medical staff at Seoul National University Hospital on 39 adults in their 20s and 30s, average intraocular pressure rose about 25 percent from before use when subjects used a smartphone in a low-light environment for 15 minutes.
The elevated state continued even after 25 minutes, and intraocular pressure tended to drop again only after use stopped. While the study is limited to 39 healthy young adults, it clearly shows that prolonged screen exposure in a dark environment can cause fluctuations in intraocular pressure.
Posture is also a variable. Looking at a screen while lying on one's side or face down in bed can act in a way that raises intraocular pressure. The normal range of intraocular pressure is generally considered to be 10 to 21 mmHg, but this figure varies by time of day, posture, and individual eye structure. People with a congenitally narrow anterior chamber angle face a higher risk even in the same environment.
If this leads to acute angle-closure glaucoma, in which intraocular pressure surges rapidly, the eye becomes severely bloodshot and may be accompanied by a splitting headache, nausea, and vomiting. Blurred vision and corneal swelling are also accompanying symptoms.
Once the optic nerve is damaged, it is difficult to fully restore with current medicine. Those with a family member who has glaucoma, or who have high myopia, diabetes, or high blood pressure, and those over 40, need regular eye examinations.
If it is hard to completely stop using a smartphone before sleep, changing the environment is a realistic alternative. Turning on a small light to reduce the difference in brightness between the screen and its surroundings, and adjusting screen brightness to match the surrounding environment, are advised.
In dark places, it is best not to use a device continuously for more than 20 minutes. Lying flat on one's back looking up at the ceiling puts less strain on the eyes than lying face down or on one's side. Placing the device out of reach rather than beside the head is also a practical measure.
If the eyes are bloodshot and dim, accompanied by headache, eye pain, and nausea, it should not be dismissed as simple fatigue. If such symptoms appear after spending a long time in a dark environment, one should keep the possibility of acute glaucoma in mind and visit an ophthalmologist without delay.
