The authors have declared that no competing interests exist.
To determine an appropriate time interval for conducting mass screening for glaucoma, it is important to gather information on the annual incidence rate. Thus, a retrospective cohort study was conducted to determine the annual incidence rate of visual field abnormalities (VFA) among a workplace cohort.
In an initial visual field test using frequency doubling technology (FDT) perimetry conducted on 3443 employees (mean age 47.4 ± 8.9, men/women = 2967/476), no abnormalities were observed. Subjects were followed-up with annual perimetric testing for seven years, with VFA being determined using FDT test (FDT-VFA).
Using the
Our data suggest that the annual incidence rate of VFA is <0.7% per year in subjects younger than 60 years of age; however, it increases to 1.6% per year in older subjects, thus suggesting that the monitoring frequency of glaucoma patients may need to be adjusted as a function of their age and be performed more frequently after the age of 60 years
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)
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
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.
The study subjects underwent a medical health check-up at the workplace. In total, 4143 subjects (mean age 48.0 ± 9.2, men/women = 3549/594) initially underwent FDT test (Humphrey FDT the first generation, C-20-1 screening mode, Carl Zeiss. Meditec Inc, Dublin, CA). Among these, 292 showed either 165 VFA on FDT testing or 33 no reliable results, or have a present history of 51 glaucoma or 43 other ophthalmic diseases. In this workplace, fundus examination had been performed before starting this study. Of the remaining 3851 subjects, 408 dropped out in the first year, leaving 3443 as subjects for this study (mean age 47.4 ± 8.9, men/women = 2967/476). Annual FDT testing was conducted over a period of seven years. We analyzed the historical records of the FDT test results. The study was approved by the Ethics Committee of Showa University, Japan.
C-20-1 test stimuli are in 17 locations within the central 20° of the visual field, including 1 central fixation point and 4 locations in each of 4 quadrants. The stimuli consist of a sinusoidal spatial waveform composed of alternative white-and-black stripes (0.25 cycle/degree, sinusoidal modulation) that counter-phase flicker at 25 Hz. The target is perceived to have twice its actual spatial frequency (frequency-doubling illusion). The screening protocol uses a suprathreshold strategy and compares the results with a normal database to indicate
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.
The follow-up numbers of subjects in their 30s, 40s, 50s, and 60s and older groups were 795, 1268, 1049, and 331, respectively. Events (FDT-VFA) occurred in 21 (2.6%), 47 (3.7%), 41 (3.9%), and 30 (9.1%) cases, respectively. Cumulative VFA rates for each age group is shown in
The rate of refractive error (myopia) in this population was 49.9%
FDT-VFA | Cumulative FDT-VFA rate (SE) at 7 years | Annual FDT-VFA rate | |||
n | case | % | |||
30's | 795 | 21 | 0.026 | 3.0 %(0.6) | 0.0042 |
40's | 1268 | 47 | 0.037 | 4.2% (0.6) | 0.006 |
50's | 1049 | 41 | 0.039 | 4.8% (0.6) | 0.0077 |
over 60 y | 331 | 30 | 0.091 | 11.3% (0.2) | 0.016 |
Total | 3443 | 139 | 0.04 | 9.0 (0.5) | 0.013 |
FDT-VFA: visual field abnormalities determined using an FDT-based glaucoma screening protocol
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:
Normal | Glaucomatous | Other disease | total | |
30's | 16 (17.6%) | 59 (64.8%) | 16 (17.6%) | 91 (100%) |
40's | 20 (12.3%) | 109 (66.9%) | 34 (20.9) | 163 (100%) |
50's | 14 (9.5%) | 104 (70.3%) | 30 (20.3%) | 148 (100%) |
over 60 y | 1 (2.3%) | 28 (60.5%) | 16 (37.2%) | 43 (100%) |
Total | 51 (11.5%) | 298 (67.0%) | 96 (21.6%) | 445 (100%) |
FDT-VFA: visual field abnormalities determined using the FDT-based protocol
Visual field impairments due to glaucoma progress slowly
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
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.