In glaucoma care, imaging is vital. It aids doctors’ ability to track progression and document change. So, its reliability must be as close to flawless as possible. That’s why researchers based out of Durham, NC sought to assess short- and long-term variability of both standard automated perimetry (SAP) mean deviation and spectral domain OCT (SD-OCT) global retinal nerve fiber layer (RNFL) thickness. 

The investigators found that long-term variability was higher than short-term variability on both technologies. “Since current event-based algorithms for detection of glaucoma progression on SAP and SD-OCT have relied on short-term variability data to establish their normative databases, these algorithms may be underestimating the variability in the long-term and thus may overestimate progression over time,” the team warned.

They evaluated 43 eyes of 43 glaucoma patients over five weeks and then annually for four years. Subjects had a mean standard deviation of 4.5±0.8 for both SAP and OCT tests for short-term variability assessment. For long-term variability, however, the same number of tests was performed, but this time, the variability was significantly higher for both tests: 1.05dB±0.70dB (vs. 0.61dB±0.34dB) for SAP mean deviation and 1.95μm±1.86μm (vs. 0.81μm±0.56μm) SD-OCT RNFL thickness.