Age strongly linked to IOP in adults in Japan
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Researchers in Japan reported sharp declines in age-related IOP, specifically in adults younger than 40 years and those older than 70 years, as well as strong associations between IOP and blood pressure and blood glucose.
“One of the objectives of this study was to confirm whether the IOP-related factors that were identified previously in epidemiological studies in Europe and [the] United States were similarly operative among the Japanese population,” Ryo Terauchi, MD, PhD, of the department of ophthalmology at the Jikei University School of Medicine in Tokyo, and colleagues wrote in the Journal of Glaucoma. “Consistent with previous reports, factors including blood pressure, blood glucose and seasonality were associated with IOP.”
Terauchi and colleagues conducted a cross-sectional study of 655,818 individuals who underwent annual checkups between April 2014 and March 2015 at 103 health care centers registered to the Japan Society of Ningen Dock, the country’s comprehensive health checkup system.
The mean age of participants was 51.5 years, with a range of 20 to 96 years, and 40.1% were women. Eligible participants had complete data for IOP, BMI, blood pressure, HbA1c and waist circumference, as well as a self-administered health questionnaire.
Although IOP measuring devices varied between facilities, all were noncontact tonometers, and readings were taken in the morning hours to minimize the effect of diurnal variation.
In all variables, significant differences were reported between men and women, researchers reported. The mean IOP of left eyes was significantly higher compared with right eyes (13.09 ± 2.94 mm Hg vs. 13.19 ± 2.96 mm Hg, P < 0.001).
In participants aged 20 to 24 years, the mean IOP in the right eye was 14.21 ± 2.95 mm Hg, with IOPs decreasing with age to 11.18 ± 2.52 mm Hg in individuals aged 90 to 96 years.
Researchers further reported a consistent and negative association between IOP and age, with a more pronounced decline in the younger than 40 years (–0.502) and 70 years and older groups (–0.674). A more gradual decline was noted in the middle-aged population of individuals, aged 40 to 69 years (–0.313).
After adjusting for covariates, researchers also noted that sex, geographic location, BMI, systolic blood pressure and fasting blood glucose were among factors associated with IOP (P < .001 in all).
“In addition to age, blood pressure and blood glucose were also found to be strongly associated with IOP,” Terauchi and colleagues wrote. “These findings would be clinically important and should be fully considered, especially in the IOP-lowering strategies for glaucoma.”
They added, “We believe that this study is a crucial step toward understanding the characteristics of IOP in more detail.”
Perspective
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It is well understood that IOP is the only practically modifiable glaucoma risk factor, and its measurement can be a trigger point for physicians diagnosing and managing the disease. This study provides some additional nuance to the IOP discussion and may suggest certain assumptions about whether the notion of glaucomatous or non-glaucomatous IOPs is a sensible one.
The Ningen Dock comprehensive checkup system in Japan provides a unique opportunity to research how age influences IOP, as well as to explore the interplay between IOP, systemic health and seasonality. The IOP decline associated with advanced aging in this study is similar to past studies in East Asia, and the positive association between IOP, systolic blood pressure, fasting plasma glucose and seasonality has been previously reported across multiple ethnicities. This study, regardless of ethnicity, underscores the complexity of systemic health’s influence on IOP and how that relationship is hard to quantify/qualify in our respective patients. Ultimately, it’s critical in practice that we recognize that IOP is dynamic and influenced by many physical and measurement variables, avoid decisions based on preconceived notions of good/bad universal IOP levels and concentrate on the specific effect of IOP on our individual patients’ optic nerves.
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