Detecting Glaucoma Progression: Trend-Based Analysis or the Rule of 5
Ophthalmology Glaucoma, November/December 2020
To evaluate glaucomatous progression, many clinicians use the “rule of 5” to gauge the rate of change in the retinal nerve fiber layer (RNFL), as seen on spectral-domain optical coherence tomography (SD-OCT). That is, a loss of 5 μm of global RNFL is considered to be evidence of progression when a follow-up scan is compared with baseline scanning results. Thompson et al. compared results derived from use of the rule of 5 with the results of trend-based analysis of SD-OCT scans. They found that trend-based analysis outperformed the rule of 5 for identifying progression in glaucomatous eyes.
For this prospective study, the researchers evaluated 300 eyes of 210 patients. The patients were followed for an average of 5.4 ± 1.5 years and were examined during a median of 11 visits (range, 7-14). All participants completed at least five SD-OCT tests during a two-year period.
Using trend-based analysis, eyes were considered to have progressed if the slope was negative and statistically significantly different from zero (p < .05). The specificity of trend-based analysis was matched to that of the rule of 5 to allow meaningful comparison of the hit rate (the proportion of glaucoma eyes categorized as progressing at each time point). The main outcome measure was the comparison between hit rates of trend analysis versus the rule of 5 when results were matched for the same specificity.
When the two methods were matched, hit rates obtained for the trend-based analysis were greater than those for the rule of 5. By comparing the two methods, the researchers determined that trend-based analysis was able to detect progression in 18.5% to 26.3% more eyes than the rule of 5 during each year of the study.
The authors acknowledge limitations in the study, including their use of global average RNFL rather than sectorial measurements to assess progression. Nonetheless, they said, trend-based analysis was superior to the rule of 5 for identifying progression and should be preferred as a method for longitudinal assessment of global SD-OCT RNFL change over time.
The original article can be found here.