OCT angiography flagged glaucoma progression 2.3 years before the field

Design

retrospective cohort study of event-based progression across three modalities

Population

180 eyes of 116 patients in the Diagnostic Innovations in Glaucoma Study, mean follow-up 5.1 years

Primary outcome

rate and timing of progression detection by OCT, OCT angiography and visual field

Effect

angiography lead time 2.3 years before field progression (95% CI 1.3 to 3.2); specificity 68.9% vs 75.6% for OCT

Eyes from the Diagnostic Innovations in Glaucoma Study with at least two years of follow-up and four or more visits on each modality were analysed for event-based progression: 180 eyes from 116 patients, 111 perimetric and 69 preperimetric, followed a mean 5.1 years. Progression on imaging required change beyond test-retest variability at two consecutive visits; field progression used guided progression analysis.

Progression was detected by at least one modality in 107 eyes (59.4%) - by OCT angiography vessel density in 58 (32.2%), by nerve fibre layer thickness in 45 (25.0%) and by visual field in 59 (32.8%). Vessel density was the earliest detector in 40 of the 107 progressing eyes (37.4%), nerve fibre layer in 32 (29.9%) and the field in 26 (24.3%). Mean lead time before field progression was 2.3 years for vessel density (95% CI 1.3 to 3.2) and 1.5 years for nerve fibre layer thickness (0.6 to 2.4); the two imaging modalities were essentially simultaneous. The cost was specificity: among 45 stable eyes, 75.6% for OCT against 68.9% for angiography.

So angiography adds lead time and adds false alarms, and the three modalities do not agree about which eyes are progressing - a third each, with substantial non-overlap. That is an argument for reading them together rather than substituting one, and against treating a single vessel-density event as grounds to escalate treatment. Before adding angiography to a monitoring protocol, be clear what a flagged eye triggers, given that roughly three in ten stable eyes were flagged too.

• Do not escalate treatment on a single OCT angiography progression event alone
• Read angiography, structural OCT and the field together - they disagree about which eyes progress
• Expect false positives: specificity was 68.9% in stable eyes
• Confirm any imaging-detected progression at the next visit before changing management
• Weigh the cost of an extra test against a lead time whose clinical benefit is unproven

Why it matters

Earlier detection is only useful if it is specific enough to act on, and this bought two years at the cost of one in three stable eyes being flagged.

Don't overread it

A retrospective cohort from a research study with intensive testing; earlier detection was not shown to improve any patient outcome.

The statistics, in plain English

A lead time interval from 1.3 to 3.2 years means the average head start is real but imprecise, and lead time only matters if acting earlier changes the outcome, which this study did not test. Specificity of 68.9% means roughly three in ten stable eyes were labelled as progressing - in a disease monitored for decades, that accumulates into a lot of unnecessary escalation. With 180 eyes and 45 stable ones, the specificity estimates themselves are imprecise.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.