Published in Glaucoma

Markers of Glaucoma Progression on OCT with Cheat Sheet

This is editorially independent content

Mar 24, 2026

Review key glaucoma progression biomarkers on optical coherence tomography (OCT) and grab the cheat sheet with imaging pearls and tips for common issues.

Differentiating true glaucomatous structural progression on optical coherence tomography (OCT) from background noise requires a solid understanding of the test-retest performance of key metrics, shifts in performance at different disease stages, and strategic use of monitoring protocols. It is especially important to understand when to utilize clustering and resetting of the baseline.

High-yield markers of glaucoma progression on OCT

The optic disc scan (RNFL): Beyond the TSNIT circle

Traditionally, peripapillary retinal nerve fiber layer (RNFL) thickness has been our primary OCT parameter for detecting and monitoring glaucoma. The locations that most frequently develop defects are inferotemporally, superotemporally, and superonasally in that order.

However, relying on summary metrics presents distinct clinical limitations:

  1. Averaging masks focal loss: Summary metrics over quadrants can mask early, focal thinning.
  2. The temporal split: The standard TSNIT display splits the temporal region—the most critical zone for macular vision—along the geometric 0° axis. This ignores the horizontal raphe, which is anatomically rotated inferiorly, making structure-function correlation more challenging on standard printouts. While some newer layouts use the NSTIN to center this sector, most clinicians must still be mindful when navigating the traditional split view to avoid missing edge-of-scan defects.

The deviation map

The deviation map can outperform the circumpapillary RNFL thickness by processing data across the whole 6x6mm area instead of just the circular tomograph. We are looking for a contiguous wedge-shaped thinning rather than scattered noise with attention to frequently involved areas. This approach offers equal or greater specificity than the circle scan because it provides topographical context—visualizing the defect extending from the posterior pole toward the disc often before it intersects the calculation circle.

The macula scan (GCC): Complementary vulnerabilities

While the optic disc scan is our traditional baseline, it is vulnerable to anatomical pitfalls that the macula often escapes. Conversely, the macula scan is vulnerable to macular pathologies like epiretinal membrane (ERM), age-related macular degeneration (AMD), and diabetic macular edema (DME), and it cannot detect glaucoma progression outside of the macular area.

Closer to the source

The macular scan (ganglion cell complex [GCC] or ganglion cell inner plexiform layer [GCIPL]) offers a distinct advantage: it measures the disease at the cellular source. This makes the GCC a more sensitive predictor of central visual field loss.

OCT Markers of Glaucoma Progression

Use this cheat sheet to familiarize yourself with signs of glaucoma progression on OCT to help detect structural glaucomatous damage early and effectively monitor patients.

Separating signal from noise with the “Rule of 5”

The utility of any quantitative measure is fundamentally limited by its precision, and discerning if a measured thinning event is true progression or measurement noise is paramount. The “Rule of 5” states that a change of 5µm in average RNFL between any two scans is likely significant.

Limits of the Rule of 5

However, relying strictly on these simplified indices has limitations. While mathematically valid at any stage, its practical utility diminishes in advanced disease. As the RNFL approaches the measurement floor, the time to detection of a 5 to 8µm drop increases while the visual field loss progresses rapidly.

Understanding trend-based analysis to monitor glaucoma progression

In contrast to event-based analysis, trend-based analysis (TBA) asks, “What is the rate of change?” This is helpful in prognosticating the likelihood and time horizon of symptomatic vision loss.

Protocols for monitoring: It’s all in the timing

Effective use of TBA relies on the relevance of the baseline to the current patient state and the timing of testing intervals.