Intraocular pressure (IOP) and visual field sensitivity peak in the winter months, especially in people with early glaucoma, according to new data presented at the 2012 ARVO meeting. The seasonal effect was much larger in regions with more extreme seasonal variations in weather.

Stuart K. Gardiner, Ph.D., from the Devers Eye Institute in Portland, Ore. and colleagues studied the trends and found a five times larger effect size in the northern states (e.g., Michigan and Minnesota) compared to the southern states (e.g., Florida and Texas). This finding is important because factors not related to glaucoma could potentially be hampering the detection of disease progression and IOP changes. 

The researchers analyzed IOP measurements and visual fields for seasonal variation collected from 33,873 visits over a median of 12.5 years made by 1,636 participants of the Ocular Hypertension Treatment Study (OHTS).

The 22 participating clinics in the OHTS study were divided into six similar geographic regions: Atlantic, Central, North, Pacific Northwest, Southeast and West. Regions were determined based on size and timing of seasonal changes in precipitation, temperature and sunlight hours.

Seasonal variations in IOP were found in all six regions; January and February were the peak months, with the size of variation ranging from 0.14mm Hg to 0.39mm Hg. In five of the six regions, statistically significant seasonal variations in visual sensitivity occurred, ranging from 0.04 dB to 0.13 dB.

Researchers believe the findings of the study will help practitioners better understand the disease and reduce clinical test-retest variability. The next step is determining whether there is a causal relationship with climatic change.