Not only does time of day affect intraocular pressure, but so does the day of the week, as shown in a new study. Photo: World Glaucoma Association. Click image to enlarge.

Studies have demonstrated the fluctuation of intraocular pressure throughout the day, with levels often peaking during the night and early morning. Taking this a step further, researchers from Tokyo recently proposed the question, “Does the day of the week also have an effect on IOP?” The answer they gathered from their study was possibly yes; especially for men, they found that mean IOP was higher on Monday and Saturday compared to Wednesday.

To conduct the large study, the research team cross-sectionally evaluated annual eye exam records from 655,818 participants (mean age: 51.5 years; 40.1% women) from 103 medical centers. A non-contact tonometer was used to measure IOP. Wednesday was used as the reference day.

The following mean IOPs were recorded from Monday to Sunday:

As the data reflects, IOP was significantly higher on Monday, Friday and Saturday than on Wednesday. After adjusting for factors affecting IOP, Friday IOP no longer showed a significant difference from Wednesday IOP, but Monday and Saturday still did. However, this trend only reached clinical significance for men and not for women.

Age also seemed to govern the influence of day of the week on IOP, the researchers observed. They found that participants younger than 65 years had higher IOPs on Monday, while those 65 or older did not.

All these findings suggest that “IOP values may have a periodic weekly pattern,” the researchers wrote in their paper for Journal of Glaucoma. “The fact that the incidence of cardiovascular disease and the value of blood pressure revealed the periodic weekly cycle may help understand the weekly IOP variation,” they explained. “Cardiovascular events and associated deaths are thought to be increased on Monday. Similarly, blood pressure and double product, consisting of systolic blood pressure multiplied by the pulse rate, is the highest on Monday.”

Another potential explanation is that IOP may be heightened on Monday due to work stress compounded with high blood pressure. Supporting this theory, the researchers pointed out in their study that “this trend was more pronounced in the male population aged <65 years with a higher employment rate.”

The elevated IOP on weekends is harder to explain. The researchers suggest it could be due to increased stress because of patients having to attend medical check-ups on the weekends, which is when many people have their only break from work for the week. It’s also possible that the higher IOP could be related to differences in behavioral patterns on weekends vs. weekdays, such as physical activity, diet, alcohol consumption and sleep duration.

While more research should be conducted to better understand how and why IOP varies on different days of the week, this study provides strong evidence that a relationship between the two likely exists.