Advancing Glaucoma Monitoring: Inner Plexiform Layer Microstructure in Focus

In late 2025, a group of researchers that included Maria Emfietzoglou, MD, and Victor S.M.C. Correa, MD, published a paper titled, “Inner Plexiform Layer Substrata Are Discernible with Commercial OCT and Affected by Aging,” in Ophthalmology Sciences, which suggested that analysis of the inner plexiform layer (IPL) and its sublayers via commercial OCT is both feasible and reproducible, and that the IPL microstructure changes with aging.

Emfietzoglou, a research fellow in ophthalmology at Massachusetts Eye and Ear, and Correa, an ophthalmology resident at the University of Missouri-Kansas City, came together with Ophthalmology Times to discuss their work, which is particularly timely as we recognize World Glaucoma Day.

Although much of glaucoma monitoring has traditionally focused on retinal nerve fiber layer (RNFL) and ganglion cell layer thickness, growing evidence suggests that synaptic and dendritic changes may precede overt neuronal loss. The IPL—a synapse-rich region where bipolar, amacrine, and ganglion cell connections converge—represents a potential window into earlier microstructural dysfunction. This study highlights a more nuanced way of assessing inner retinal health and potentially raises questions about whether advanced IPL analysis could enhance early detection, risk stratification, and longitudinal monitoring of disease progression beyond thickness metrics alone.

The Study Findings

In their cross-sectional study, Emfietzoglou, Correa, and colleagues evaluated whether the IPL can be reliably stratified using commercially available spectral-domain OCT and whether its microstructure changes with aging. The IPL is a synapse-rich retinal layer critical for visual signal integration, traditionally described histologically as consisting of 5 strata. Althu prior work has visualized IPL sublayers using experimental imaging systems, this study sought to determine whether similar detail could be discerned using a widely available commercial OCT platform combined with semiautomated image analysis.

The investigators analyzed 92 healthy participants who underwent enhanced high-definition macular OCT imaging. Using ImageJ and Python-based analysis, they evaluated signal intensity profiles across a standardized nasal macular region (1000–2500 μm from the foveal center). The IPL consistently demonstrated a multilayered pattern composed of 3 hyperreflective and 2 hyporeflective bands arranged in alternating fashion. Quantitative metrics included signal intensity of individual bands, contrast between adjacent sublayers, relative distances between bands, the percentage of IPL segments with identifiable stratification, and mean squared error (MSE) as a measure of contrast variance.

Aging was associated with several distinct structural changes. Most notably, there was a significant increase in signal intensity within the hyporeflective bands—particularly the outer hyporeflective band—while hyperreflective band intensity remained relatively stable. This shift resulted in an overall reduction in contrast between adjacent sublayers, producing a flatter intensity profile in older individuals. Importantly, the relative distances between IPL bands did not significantly change with age, suggesting that the laminar organization remains spatially preserved despite alterations in reflectivity.

Older participants also demonstrated a lower percentage of IPL segments with clearly identifiable 5-band stratification and reduced contrast variance within the layer, reflected by lower MSE values. In parallel, aging correlated with thinning of the inner retina, including significant reductions in IPL thickness, as well as thinning of the nerve fiber layer and ganglion cell complex, with the strongest association observed in the IPL itself.

From a reliability standpoint, the analysis showed high intraeye and intereye repeatability for most key parameters, particularly contrast measures and MSE, supporting the reproducibility of IPL stratification using this approach.

Final Takeaway

Overall, the study demonstrates that IPL sublayers are discernible using commercial OCT technology and that aging is associated not only with IPL thinning but also with measurable reductions in sublayer contrast and stratification clarity. These findings suggest that beyond thickness alone, more comprehensive IPL microstructural analysis may offer potential as a biomarker for early synaptic dysfunction and neurodegenerative processes affecting the retina.

REFERENECE
1. Correa VSMC, Emfietzoglou M, Sakuno G, et al. Inner Plexiform Layer Substrata Are Discernible with Commercial OCT and Affected by Aging. Ophthalmology Sci. 2025;5(5):100815. doi:10.1016/j.xops.2025.100815