Published in Research

Study: IOP levels are dependent on the day of the week

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4 min read

Recent findings from a study published in the Journal of Glaucoma evaluated the link between intraocular pressure (IOP) by day of the week using data from the Japan Ningen Dock Study (JSND).

Give me some background first.

As IOP reduction is currently the only proven treatment for glaucoma, understanding how IOP fluctuates is key for managing glaucoma progression.

While it is known that IOP varies during the day, a research team from Tokyo sought to elucidate whether it varies weekly as well.

What is the JSND?

The Ningen Dock is a comprehensive health checkup system unique to Japan, wherein an estimated 3 million Japanese individuals are enrolled per year.

The system’s examinees undergo comprehensive annual physical and ophthalmic examinations, which include measuring:

  • Visual acuity (VA)
  • Tonometry
  • Fundus photography

As such, the JSND collects large-scale IOP data from Monday to Sunday to measure weekly IOP variations.

Now, talk about the study.

In this cross-sectional study, investigators assessed the data of annual health checkup examinees between April 2014 and March 2015 from the JSND.

The IOP was measured using a non-contact tonometer, and the mean IOPs of each day of the week were compared using multiple comparison tests and linear regression analyses.

Anything else?

Wednesday was set as the reference, and investigators evaluated IOP variations stratified by sex and age.

Additionally, in order to externally validate the data, a secondary single-center study that used an identical tonometry device and method was performed.

Talk about the cohort.

In total, the study included 655,818 participants from 103 medical centers; the mean age was 51.5±10.5 (range 20-96 years), and 40.1% of examinees were women.

Findings?

Overall, IOP was notably higher on Monday, Friday, and Saturday in comparison to Wednesday (P<0.001, P<0.001, P=0.002).

The mean IOPs by day of the week were as follows:

  • Monday: 13.19±2.97 mmHg
  • Tuesday: 13.06±2.92 mmHg
  • Wednesday: 13.05±2.91 mmHg
  • Thursday: 13.05±2.92 mmHg
  • Friday: 13.12±2.94 mmHg
  • Saturday: 13.10±2.96 mmHg
  • Sunday: 13.16±2.78 mmHg

Tell me more.

After adjusting for factors affecting IOP, the mean IOPs on Monday and Saturday were higher than those on Wednesday (β=0.097, 95% confidence interval [CI] 0.074-0.121, P<0.001; β=0.032, 95% CI 0.005-0.059, P=0.019).

This trend was also observed in the secondary study population.

How did gender impact mean IOP measurements?

Men had significantly higher IOPs on Monday and Saturday than on Wednesday (β=0.142, 95% CI 0.110-0.173, P<0.001; β=0.053, 95% CI 0.017-0.089, P=0.004).

Conversely, women did not have a significant trend in mean IOP by day of the week.

What about age?

Participants aged <65 years had higher IOPs on Monday (P<0.001 for those under 60 years, P=0.003 for 60-64 years), while examinees aged >65 years did not (P=0.856).

How does this connect to weekly trends in cardiovascular events?

Interestingly, cardiovascular events and associated deaths, as well as blood pressure and double product (which consists of systolic blood pressure multiplied by the pulse rate), were highest on Monday.

Further, findings from a 2022 study indicated that higher systemic blood pressure might influence IOP elevation in Japanese populations.

Expert opinion?

Consequently, the sex- and age-based disparities mentioned above could be related to the psychosocial stress associated with work to cause IOP fluctuation, as reported for cardiovascular disease and blood pressure.

According to the study authors, “Elevated IOP on weekends is difficult to explain but may be caused by the loss of holidays due to health checkups.”

Take home.

These findings indicate that IOP values may have a cyclical weekly pattern, with the highest mean IOP reported on Monday for men aged <65 years.

Although further research into weekly IOP fluctuations is warranted, this study provides an important step for providing a more nuanced understanding of IOP variation.