Significant Glaucomatous Visual Field Progression in the First Two Years: What Does It Mean?

Abstract

PurposeIt has been recommended that multiple visual field examinations be performed in the first 2 years after glaucoma diagnosis so that rapid visual field progression (≤−2 dB/year, using ordinary least squares regression over time of the summary index mean deviation [MD]) can be detected. Here I investigate how predictive a statistically significant regression slope is of truly rapid visual field progression.MethodsI simulated visual field series (N = 100,000) spaced at 4 monthly intervals for the first 2 years. MD values had a standard deviation of 1 dB. The true underlying rates of progression were selected from a modified hyperbolic secant with parameters averaged from fits to large data sets from Canada, Sweden, and the United States.ResultsThe positive predictive value (PPV) for rapid progression was 0.47 after 2 years, whereas the negative predictive value (NPV) was > 0.99. When using the criterion that a significant regression also had to have a slope of ≤ −2 dB/year, the PPV for rapid progression reduced substantially to 0.18 but the NPV was essentially unchanged (NPV >0.99).ConclusionAlthough performing multiple visual fields in the first 2 years provides appropriate power to detect rapid progression, a significant regression slope in the first 2 years is not highly predictive of rapid progression, particularly so if slopes ≤ −2 dB/year are considered only.Translational RelevanceStatistically significant visual field progression in a short period after diagnosis may not necessarily indicate the presence of rapid progression, and so confirmatory signs of rapid progression should be sought before implementing treatment changes.

Detecting glaucomatous progression with infrequent visual field testing

“…It is clear that slope estimates are highly variable with small visual field series, and so in a research setting it is advisable to obtain an extended visual field series before performing regression analyses. However, as has been argued previously, clinicians will likely examine a patient's visual field series at each patient visit, and so examining the performance of regression analyses from the first point they can be performed (that is, three or more fields) is appropriate.…”

“…This lack of a strong prediction reflects, in large part, that the prevalence of rapid visual field progression is low in glaucoma . The positive predictive value was also less than 0.5 for a lower – but still troubling – rate of progression of −1 dB year −1 or worse …”

“…This finding has been influential in shaping glaucoma management guidelines for how frequently visual field assessments are performed . Although multiple visual field assessments provide appropriate statistical power, it has recently been suggested that a finding of a significant slope when regressing a patient's MD values over time does not have a high positive predictive value (PPV) for detecting rapid progression . At 2 years, the PPV for rapid progression was around 0.1: that is, around one in 10 people showing a significant regression slope in the first 2 years had underlying true rates of progression of −2 dB year −1 or worse .…”

“…Although multiple visual field assessments provide appropriate statistical power, it has recently been suggested that a finding of a significant slope when regressing a patient's MD values over time does not have a high positive predictive value (PPV) for detecting rapid progression . At 2 years, the PPV for rapid progression was around 0.1: that is, around one in 10 people showing a significant regression slope in the first 2 years had underlying true rates of progression of −2 dB year −1 or worse . This lack of a strong prediction reflects, in large part, that the prevalence of rapid visual field progression is low in glaucoma .…”

“…However, there are some limitations with this recent study of the PPV of a significant regression slope . The simulation in the study assumed visual fields were tested at four‐monthly intervals in the first 2 years, in keeping with several current guidelines .…”