Researchers from Duke University warn that algorithms for standard automated perimetry and spectral-domain optical coherence tomography may overestimate glaucoma progression over time.
The study included a total of 43 eyes of 43 glaucoma subjects. The patients had a mean of 4.5 ±0.8 SAP and OCT tests for short-term variability assessment. For long-term variability, the same number of tests were performed; results were collected annually over an average of 4 ±0.8 years.
Ordinary least-squares linear regression of SAP mean deviation and SD-OCT global retinal nerve fiber layer thickness were fitted over time for sequential tests conducted within five weeks (short-term testing) and annually (long-term testing). Residuals were obtained by subtracting the predicted and observed values, and each patient’s standard deviation of the residuals was used as a measure of variability. The Wilcoxon signed-rank test was performed to test the hypothesis of equality between short- and long-term variability.
The average standard deviation of the residuals was significantly higher in the long-term than in the short-term period for both tests: 1.05 ±0.70 dB vs. 0.61 ±0.34 dB, respectively (p<0.001) for SAP MD and 1.95 ±1.86 µm vs. 0.81 ±0.56 µm, respectively (p<0.001) for SD-OCT RNFL thickness. The researchers remark that this may have significant implications when determining whether or not true progression has occurred when using event-based algorithms to assess progression. They theorize that the factors explaining differences between long- and short-term variability according to levels of damage are likely to be related to the precision of the instruments at different levels of disease and the dynamic range of the tests. They also suggest that subjects followed over the long term may be less motivated and will likely be tested under different conditions each time.
Amer J Ophthalmol 2020;210:19-25.
Wubben TJ and Johnson MW. For the Anti-VEGF Treatment Interruption Study Group.
The Great Outdoors vs. Myopia
After implementing a new initiative to promote increased time outdoors to stave off myopia progression, researchers in Taiwan found that the policy was successful in reversing the long-term trend of increased low visual acuity in the country’s schoolchildren.
This prospective cohort study evaluated data from the Taiwan School Student Visual Acuity Screen (TSVAS), which required each school in Taiwan to measure uncorrected VA in students in grades one through six every half year in a period stretching from 2001 to 2015. An ucorrected visual acuity of 20/25 or less was considered reduced visual acuity for purposes of the evaluation.
From 2001 to 2011, the team discovered that the prevalence of reduced visual acuity in schoolchildren increased from 34.8 percent to 50 percent. After instituting a program in September 2010 that encouraged schools to take students outdoors for two hours every day for the purposes of myopia prevention, they noted that the prevalence decreased from 49.4 percent in 2012 to 46.1 percent in 2015.
Controlling by gender and grade, the investigators observed a significant constant upward trend in the mean annual change in prevalence before the intervention and a constant decrease of -2.34 percent annually afterward.
The researchers say that since the efficacy of increased time outdoors in slowing the onset of myopia has been demonstrated in randomized trials, interventions to promote increased time outdoors may be useful in other areas affected by an epidemic of myopia. REVIEW
Ophthalmology February 7, 2020. [Epub ahead of print].