Are Visual Fields Progression Rates Being Underestimated?

Trend analysis of targeted mean total deviation (TMTD) is more effective than trend analysis of global indices for evaluating visual field (VF) progression in patients with severe glaucoma, according to a study published in the Journal of Glaucoma. 

According to the research, trend analysis of VF global indices may underestimate the rate of progression in patients with advanced glaucoma due to the effect of test points without detectable sensitivity. In this single-center cohort study, researchers compared the rates of change of VF global indices with and without undetectable points at different stages of glaucoma. 

They calculated TMTD via averaging total deviation except points which were consistently undetectable. Participants were separated into 4 subgroups according to baseline mean deviation (MD): early (≥-6 dB), moderate (-6 dB to -12 dB), advanced (-12 dB to -20 dB), and severe (<-20 dB). In each stage, the rates of change of MD and TMTD were statistically compared.

The study included 648 eyes of 366 patients with glaucoma who were evaluated between January 2004 and February 2020 at Osaka University Hospital, in Japan. The mean age ± SD at baseline was 56.9±11.9 years. In total, 298 eyes were categorized as early, 174 eyes were moderate, 142 eyes were advanced, and 34 eyes were severe. 

Researchers found that MD slope (-0.34 dB/year) in severe glaucoma was significantly slower than TMTD slope (-0.42 dB/year, P =.028) and was slower than MD slopes in the other stages. They observed that differences between MD slopes and TMTD slopes were most pronounced in patients with MD values less than -25 dB (P =.002).

“Undetectable locations in eyes with severe glaucoma may lead to an underestimate of the rates of VF progression,” according to the researchers. “Trend analysis of TMTD rather than global indices offers a practical and simple approach for alleviating underestimation of VF progression in severe glaucoma.”

Study limitations include the inclusion of only Japanese patients, the retrospective design, and a relatively small cohort of patients with severe glaucoma. 

“In late-stage glaucoma, estimating the rate of VF progression is of vital importance, but especially challenging,” according to researchers. “Therefore, reliable methods for evaluating the progression of severe glaucoma are needed.”

Reference

Miki A, Okazaki T, Weinreb RN, et al. Evaluating visual field progression in advanced glaucoma using trend analysis of targeted mean total deviation. J Glaucoma. Published online January 12, 2022. doi:10.1097/IJG.0000000000001985