Frequency of Testing to Detect Visual Field Progression Derived Using a Longitudinal Cohort of Glaucoma Patients

Abstract

Purpose: To determine the time required to detect statistically significant progression for different rates of visual field loss using standard automated perimetry (SAP) when considering different frequencies of testing using a follow-up scheme that resembles clinical practice.

Design: Observational cohort study.

Participants: One thousand seventy-two eyes of 665 patients with glaucoma followed up over an average of 4.3±0.9 years.

Methods: Participants with 5 or more visual field tests over a 2- to 5-year period were included to derive the longitudinal measurement variability of SAP mean deviation (MD) using linear regressions. Estimates of variability then were used to reconstruct real-world visual field data by computer simulation to evaluate the time required to detect progression for various rates of visual field loss and different frequencies of testing. The evaluation was performed using a follow-up scheme that resembled clinical practice by requiring a set of 2 baseline tests and a confirmatory test to identify progression.

Main outcome measures: Time (in years) required to detect progression.

Results: The time required to detect a statistically significant negative MD slope decreased as the frequency of testing increased, albeit not proportionally. For example, 80% of eyes with an MD loss of -2 dB/year would be detected after 3.3, 2.4, and 2.1 years when testing is performed once, twice, and thrice per year, respectively. For eyes with an MD loss of -0.5 dB/year, progression can be detected with 80% power after 7.3, 5.7, and 5.0 years, respectively.

Conclusions: This study provides information on the time required to detect progression using MD trend analysis in glaucoma eyes when different testing frequencies are used. The smaller gains in the time to detect progression when testing is increased from twice to thrice per year suggests that obtaining 2 reliable tests at baseline followed by semiannual testing and confirmation of progression through repeat testing in the initial years of follow-up may provide a good compromise for detecting progression, while minimizing the burden on health care resources in clinical practice.