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Re: Lee et al.: Greater physical activity is associated with slower visual field loss in glaucoma (Ophthalmology. 2018 Oct 10 [Epub ahead of print])

      To the Editor:
      We read the article by Lee et al,
      • Lee M.J.
      • Wang J.
      • Friedman D.S.
      • et al.
      Greater physical activity is associated with slower visual field loss in glaucoma.
      in which they monitored the physical activity (PA) of glaucoma suspects or manifest glaucoma and analyzed the association between PA levels and the rate of visual field loss. Using a longitudinal dataset, they took advantage of an efficient statistical method to deal with the risk factors, finally concluding that increased PA time, such as walking, moderate-to-vigorous PA, and nonsedentary activity, were associated with slower rates of visual field damage in treated glaucoma patients. This finding is very important, indicating that exercise may be another modifiable risk factor (besides intraocular pressure) to help prevent progressive glaucoma loss. However, after a careful read, we began to have doubts on the paper’s methodology and reliability.
      The study used 1-week PA data measured several years ago (about 7–9 years ago) to stand for patients’ daily PA and made the assumption that their exercise habits have remained the same over time, which is not appropriate. Additionally, the researchers were not strict with their requirements for valid PA data, including participants’ data for analysis as long as they wore their device for >8 h/d for >2 days. In the short run, measured PA data may not be reliable, because data can be easily influenced by factors such as weather, whether one swims or not, the day (weekend vs weekday), and even mood. Even in the long term, the exercise habits of patients may fluctuate for various reasons, such as systemic diseases, age, change in living conditions, or even injuries. Most important, participants, armed with the knowledge that exercise is associated with good health, may adjust their exercise habits during the study. All these factors make it difficult for researchers to accurately measure patients’ daily PA. Therefore, it would be better to use measured PA data in the present to represent daily exercise habits.
      In conclusion, it is difficult for researchers to accurately measure the daily PA of patients for a long time. One week of monitored PA data can reliably stand in for an individual’s daily exercise habit. However, it is better to use measured PA data in the present in investigating the relationship between PA time and the rate of visual field damage.

      Reference

        • Lee M.J.
        • Wang J.
        • Friedman D.S.
        • et al.
        Greater physical activity is associated with slower visual field loss in glaucoma.
        Ophthalmology. 2018 Oct 10; ([Epub ahead of print])

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