Lower air temperatures may be associated with an increase in the fluid pressure inside the eye—a major cause of glaucoma—and should be considered when treating patients with the condition, according to findings published online in the British Journal of Ophthalmology.

People with more severe glaucoma seem to be more susceptible to the effects of ambient temperature, the findings suggest.

Glaucoma is usually caused by a buildup of pressure in the eye. This damages the optic nerve, which connects the eye to the brain. It is most common in people over 50 and can cause vision loss if not diagnosed and treated early.

A healthy eye has an intraocular pressure between 10 and 20 mmHg.

Previously published studies have investigated the potential link between intraocular pressure and climatic factors in the general public. But it was not clear whether specific climatic factors affect eye pressure in people with stable glaucoma who are receiving treatment.

Tracking treated patients over time

To find out, the researchers reviewed the medical records of 77 patients with primary open-angle glaucoma (the most common form) who were treated at a university hospital in Japan between January 2012 and December 2023.

Only patients over 40 who had no history of eye surgery and had three or more clinic appointments a year for at least three years were included in the study.

To rule out the effects of changes in medical treatment, participants had to have used one to four antiglaucoma eye drops daily in both eyes, without any change during the study period.

Intraocular pressure, blood pressure and heart rate were measured in each patient. Corneal measurements were also taken because thin corneas are an independent risk factor for faster disease progression.

A total of 2,655 intraocular pressure measurements from 154 eyes of 77 patients were included in the final analysis. The patients’ average age was 65, and they were monitored for an average of around five years.

Climatic data for the study period were obtained from the Japan Meteorological Agency, including air temperature, humidity, wind speed, precipitation and sunlight duration.

The researchers accounted for other factors to assess whether changes in eye pressure were linked to the weather rather than factors such as age, gender or central corneal thickness.

Colder days, higher eye pressure

The analysis showed that air temperature was significantly and independently associated with intraocular pressure readings.

A lower ambient air temperature was associated with a significant increase in intraocular pressure. A decrease in ambient temperature of 35°C was associated with a 1 mmHg increase in intraocular pressure.

As expected, higher blood pressure was also linked to higher intraocular pressure.

Severe glaucoma showed stronger links

In further analysis, the researchers found that air temperature was significantly associated with intraocular pressure only in patients who had severe glaucoma or used multiple eye drops.

Further research involving larger groups of people is needed to confirm whether air temperature might be influential in people with mild glaucoma or in those using only one type of eye drop, the researchers said.

This is an observational study and, as such, can’t establish cause and effect. The researchers also acknowledge that potentially important lifestyle factors, such as exercise and obesity, weren’t taken into account. No patients with poorly controlled intraocular pressure were included in the study.

“The relationship between intraocular pressure and ambient temperature in patients with stable primary open-angle glaucoma under medical treatment should be considered in a comprehensive treatment strategy,” the researchers conclude.

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