Glaucoma is a relatively common ocular disease characterized by optic neuropathy and is believed to be present only when at least one eye has both typical structural and functional defects (optic disc damage and visual field loss)1 Within an aging society, glaucoma-induced visual field defects have a particular impact on quality of life (QOL) 2, and their prevention is an important public health concern 3. Characteristics of glaucoma depend on race 4, and in the Japanese population the dominant form of this condition is primary open angle glaucoma (POAG)—particularly normal tension glaucoma (NTG) accounting for more than 90% of POAG 5.

Glaucoma mass screening is an important public health concern, because the number of patients suffering from glaucoma, but not being medically treated, were estimated to be 80% in Japan 5. Previously, we demonstrated the efficacy of screening based on frequency doubling technology (FDT), with a greater than 70% positive predictive value for glaucoma, including “glaucoma suspect” in the workplace 6. Given that the test subjects were relatively young, healthy workers with a lower prevalence of illnesses such as diabetes mellitus or cataracts, these findings indicated that visual field abnormalities (VFAs) identified by the FDT test were mainly related to glaucoma in this study population.

When planning to conduct mass screening, information on the prevalence is required, as the screening performance depends on it. In addition, to determine an appropriate time interval for conducting screening, information on the annual incidence is important. Therefore, the present study was conducted to estimate the annual incidence of new VFA detected by FDT testing.

Information on refractive errors was obtained by checking for the presence of refractive errors (use of eyeglasses or contact lenses for myopia) by a nurse on the basis of a self-report.

Cumulative FDT-VFA rates were calculated using the Kaplan–Meier method. Significance was determined by the log-rank test. When a subject did not receive an FDT test during a particular year, but the result of the FDT test was normal in the following year, the result was considered to be normal for the previous year as well. All statistical analyses were performed using IBM-SPSS software version 22.0 (IBM SPSS, Tokyo, Japan). P < 0.05were considered statistically significant.

To the best of our best knowledge, the present study is the first report to estimate the annual incidence of VFA as determined by annual FDT tests among a large Asian population utilizing a follow-up study design.

For subjects in their 40s, 50s, and ≥60s, our data show a seven-year incidence rate of VFA of 4.2%, 4.8%, and 11.3%, respectively. Based on our previous study, the positive predictive values of the FDT test for glaucoma suspects were 0.67, 0.70, and 0.61 in the corresponding age groups (Tatemichi, unpublished data: supplement table). Thus, the seven-year incidence of glaucoma patients can be roughly estimated to be 2.8%, 3.4%, and 6.9% in the 40s, 50s, and ≥60s age groups, respectively. Recently, Kim et al reported the five-year incidence of Primary Open Angle Glaucoma in a cohort study 9. According to their results, the five-year incidence was 0.82%, 1.16%, 1.27%, and 4.31% for individuals in their 40s, 50s, 60s, and ≥70s, respectively. Compared with the analysis by Kim et al, we observed a higher incidence in our study. We believe that this discrepancy may have occurred for several reasons. First, the incidence of VFA could be increased in correlation with examination frequency. This study examined visual fields with FDT testing a maximum seven times. Second, the other study’s glaucoma screening program was based on intraocular pressure (IOP) measurements and fundus photography 9. However, among the Asian population, normal tension glaucoma is dominant 510 and glaucoma mass screening based on IOP is not sufficiently sensitive 5. In addition, FDT test could detect other diseases such as cataracts, diabetic retinopathy, brain tumor and so on. 6. Third, our study population was limited to a workplace cohort. Another previous study showed that the major risk factors for glaucoma included myopia 1112. Our study population was associated with a higher prevalence of myopia; this risk factor applied to our study population, and might have contributed to the higher incidence of VFA observed.

Visual field impairments due to glaucoma progress slowly 1. From the viewpoint of cost-effectiveness, it is important to determine an appropriate screening interval when planning mass screening for glaucoma. Furthermore, such mass screening requires a high performance in the positive predictive value, which depends on the prevalence. Hence, our study provides important data to be considered when planning to screen for glaucoma in the workplace.

It is important to highlight several limitations of the present study. First, major limitation of this study is not to obtain a complete ophthalmic examination on VFA as determined by FDT. Therefore, further studies are required. However, our study aimed to provide information on the annual rate of VFA, which would enable the planning of a mass screening using the FDT test. Second, our workplace study population included a very few women compared with the general population. Thus, careful interpretation of our results is necessary before they can be applied to the general population; however, no significant difference was observed in the prevalence of glaucoma between Japanese men and women 5.

In conclusion, the annual incidence of VFA is less than 0.7% per year in subjects younger than 60 years old, but increases to 1.6% per year for older subjects, thus suggesting that the monitoring frequency of glaucoma patients may need to be adjusted as a function of their age and should be performed more frequently after the age of 60 years.