Pressure in treated glaucoma ran slightly higher in cold weather

Design

Retrospective single-centre longitudinal cohort

Population

154 eyes of 77 patients with stable medically treated primary open-angle glaucoma

Primary outcome

Intraocular pressure by ambient temperature

Effect

Estimate -0.029 mmHg per °C (p = 0.003)

A retrospective study in the British Journal of Ophthalmology (published 29 September) analysed 2,655 Goldmann pressure readings from 154 eyes of 77 patients with stable, medically treated primary open-angle glaucoma in Kyoto, followed for about five years with no change in treatment.

After adjusting for a wide range of factors including blood pressure, time of day, season and weather, intraocular pressure fell slightly as ambient temperature rose (about 0.03 mmHg per degree Celsius). Higher mean blood pressure was linked to higher pressure.

The effect is small: a 20-degree difference between winter and summer corresponds to roughly half a millimetre of mercury. But it may explain some apparent fluctuation between visits and why a reading in winter is higher than the summer before. It is a single-centre study in one climate.

• Consider season and ambient temperature when interpreting a small rise in pressure in a stable patient.
• Compare pressure readings taken at similar times of day and year where possible.
• Check blood pressure, which was also linked to intraocular pressure in this cohort.
• Do not escalate treatment on a single winter reading without confirming a trend.

Why it matters

It offers one explanation for visit-to-visit variation that can prompt unnecessary changes in treatment.

Don't overread it

The effect is small and was found in one Japanese centre; it may not apply in other climates.

The statistics, in plain English

An estimate of -0.029 means intraocular pressure dropped by about 0.03 mmHg for every one-degree rise in temperature. The p-value shows the association is unlikely to be chance, but its clinical size is small.

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