Greater visual impairment is known to be associated with lower levels of physical activity1 and previous studies have demonstrated that more severe VF damage may be associated with lower overall levels of daily measured physical activity.2 In this study, E et al. build off these previous findings by examining and quantifying specific patterns of daily physical activity in patients with glaucoma with varying levels of visual field damage. Authors used an accelerometer to track patterns of activity over the course of the day to calculate 'activity fragmentation' (the probability of transitioning from an active state to a sedentary state), a relatively novel measure of physical activity which has been used to assess overall fitness and functional status.3,4
Patients with the most severe VF damage were found to spend the shortest periods of time in activity, [Each 5-dB decrement in IVF sensitivity was associated with 16.3 fewer active minutes per day (95% CI, 28.4 to 7.1 mins)] and had the most fragmented physical activity, transitioning out of an active state to a sedentary state more rapidly. Greater VF damage was associated with a more rapid transition (i.e., the more severe the VF damage, the more rapid this transition). This suggests that the overall lower level of physical activity among patients with worse VF damage5 is specifically driven by shorter sustained bouts of activity.
This study's ability to explore physical activity in great detail is afforded by the use of accelerometry. Accelerometers allow for the objective measurement of physical activity, and provide a richness of longitudinal data which can be used to explore nuanced patterns in activity. Using this approach, the authors ultimately lend us a more thorough understanding of the lifestyle habits of our patients with VF damage.
Clarifying the direction and causality of the association between physical activity (a modifiable risk factor) and glaucoma would have potentially substantial implications for the nature of glaucoma care and patient counselling
There are, however, multiple factors which may also be driving this association, including poor fitness, low overall health, multi-comorbidity, season and geography, which may influence both physical activity and VF. Furthermore, the study design is limited in its ability to assess the temporality of the relationship, or identify on potential causality in the association between physical activity and VF.
With recent genome-wide association studies identifying several loci associated with physical activity and sedentary behavior,6 it may be possible to carry out Mendelian randomization studies to examine causal relationships between activity level and glaucoma (and related traits such as IOP, and VF damage). Clarifying the direction and causality of the association between physical activity (a modifiable risk factor) and glaucoma would have potentially substantial implications for the nature of glaucoma care and patient counselling.