Lower air temperatures may be associated with an increase in the fluid pressure inside the eye—a cardinal cause of glaucoma—and should be taken into consideration when treating patients with the condition, suggest the findings of research 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 build-up of pressure in the eye. This damages the optic nerve that connects the eye to the brain. It is most common in the over 50s and can cause vision loss if not diagnosed and treated early.
A normal healthy eyeball has an intraocular pressure of 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 if specific climatic factors affect eye pressure in people with stable glaucoma who are receiving treatment for their condition.
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 aged over 40, with no history of eye surgery, and who had three or more clinic appointments a year for at least three years were included in the study.
To rule out the effects of any change in medical treatment, study 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. Cornea measurements were also taken as thin corneas are an independent risk factor for faster disease progression.
A total of 2655 intraocular pressure measurements, taken from 154 eyes of 77 patients, were included in the final analysis. Their average age was 65 and they were monitored for an average of around 5 years.
Climatic data for the study period was obtained from the Japan Meteorological Agency including air temperature, humidity, wind speed, precipitation, and sunlight duration.
The researchers corrected for other factors to make sure the change in eye pressure was linked to the weather rather than factors, such as age, gender, or central corneal thickness.
Analysis of the results showed that air temperature was significantly and independently associated with pressure readings from the eye.
A lower ambient air temperature was associated with a significant increase in intraocular pressure. A decrease in ambient temperature of 35°C is associated with a 1 mmHg increase in intraocular pressure.
As expected, higher blood pressure was also linked to higher intraocular pressure.
In further analysis the researchers found that air temperature was significantly associated with intraocular pressure only in patients who had severe glaucoma or who were using 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, say the researchers.
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 either.
"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.
