Inner plexiform layer substrata: Possible biomarker of retinal health

A recent study¹ suggested that the microstructure of the inner plexiform layer (IPL) may be an important biomarker for early diagnosis and monitoring of diseases, such as glaucoma, affecting synaptic health in this layer. Commercially available optical coherence tomography (OCT) and a semiautomated segmentation program made this visualization possible, according to first co-authors Victor SMC Correa, MD, and Maria Emfietzoglou, MD.

They are from the Ines and Fredrick Yeatts Retina Research Laboratory at Mass Eye and Ear and Harvard Medical School, Boston. This research was conducted under the supervision of Demetrios G. Vavvas, MD, PhD, the Solman and Libe Friedman Professor of Ophthalmology, from the Ines and Fredrick Yeatts Retina Research Laboratory at Mass Eye and Ear and Harvard Medical School, and Alexander Charonis, MD, from Athens Vision Eye Institute, Athens, Greece. Correa is presently an ophthalmology resident at the University of Missouri-Kansas City, Kansas.

“Aging negatively impacts synaptic health, and synaptic dysfunction contributes to various eye diseases, like glaucoma, and neurodegenerative disorders, including Alzheimer disease and Parkinson disease.^2-5 Advanced imaging technologies, particularly spectral-domain OCT, offer high-resolution, cross-sectional imaging of the human retina, providing a unique opportunity for in vivo noninvasive assessment of human synapses,” the authors explained.

The findings were published in Ophthalmology Science.¹

Differentiating the sublayers of the IPL has historically been challenging due to their subtle contrast relative to adjacent retinal layers. Only a few previous studies, using experimental OCT systems, have successfully differentiated these sublayers.

“Unlike earlier studies using experimental OCT platforms,^6-10 this investigation used a widely available commercial system, making clinical translation more feasible,” explained Emfietzoglou.

IPL study methodology

This cross-sectional investigation, conducted at the Athens Vision Eye Institute, Athens, Greece, under the supervision of Dr. Charonis, from January to July 2024, used a commercial OCT instrument (Optovue Avanti SD-OCT) and a semiautomated image analysis program (ImageJ) to measure the IPL thickness and analyze the hyperreflective and hyporeflective bands within the IPL.

The goal was to determine the thickness and reflectivity patterns of the IPL and changes that occur with aging in 92 healthy individuals (median age, 57 ± 19.5 years); 52% were women.

The primary outcome measures were the signal intensity of the IPL, the contrast between the hyperreflective and hyporeflective bands, and the percentage of IPL with identifiable sublayers. The secondary outcomes included the inner retinal thickness measurements, including the IPL, nerve fiber layer (NFL), and ganglion cell complex (GCC), the investigators recounted.

What did the IPL analysis find?

The IPL exhibited a multilayered structure with five sublayers, three hyperreflective and two hyporeflective, arranged in an alternating pattern. Aging was associated with higher signal intensity from the hyporeflective bands and minimal changes in the hyperreflective bands, resulting in an overall reduced contrast between the five sublayers.¹

“Older participants showed a lower percentage of IPL with identifiable sublayers, along with a lower contrast variance within the IPL. Aging also was correlated with reduced inner retinal thickness, including the IPL, NFL, and GCC, with a stronger association for the IPL. The IPL exhibited high intra-eye and inter-eye repeatability, with significant correlations and nonsignificant mean differences observed in most key parameters,” the investigators reported.

Based on their results, they concluded that the analysis of the IPL was feasible and repeatable using commercial OCT technology, as the five sublayers of the IPL, both hyperreflective and hyporeflective, were clearly visualized.

“This is the first study to demonstrate IPL sublayer stratification using commercial OCT in a large aging cohort,” said Emfietzoglou. “Our findings suggest that subtle changes in synaptic architecture may be detected earlier than previously thought, which could transform how we monitor diseases like glaucoma and Alzheimer’s.”

Increasing evidence from experimental studies has suggested that synaptic alterations may occur before significant loss of axons and neurons, prompting a focus on the IPL as an early biomarker for diseases affecting synaptic health. “However, previous studies have primarily concentrated on the IPL thickness, which may not fully capture the early changes in the IPL associated with neurodegeneration. A more comprehensive assessment of the IPL, incorporating additional features such as those included in the present analysis, could provide valuable insights for the early diagnosis and monitoring of neurodegenerative diseases,” the investigators concluded.

References

1. Correa VSMC, Emfietzoglou M, Sakuno, MD, PhD, et al. Inner plexiform layer substrata are discernible with commercial OCT and affected by aging. Ophthalmol Sci. 2025;5:100815. https://www.ophthalmologyscience.org/article/S2666-9145(25)00113-7/fulltext

2. Agostinone J, Di Polo A. Retinal ganglion cell dendrite pathology and synapse loss: implications for glaucoma. Prog Brain Res. 2015;220:199-216.

3. Almasieh M, Wilson AM, Morquette B, et al. The molecular basis of retinal ganglion cell death in glaucoma. Prog Retin Eye Res. 2012;31:152-81.

4. Alix JJP, Domingues AMde J. White matter synapses: form, function, and dysfunction. Neurology. 2011;76:397-404.

5. Hamos JE, DeGennaro LJ, Drachman DA. Synaptic loss in Alzheimer's disease and other dementias. Neurology. 1989;39:355-61.

6. Tanna H, Dubis AM, Ayub N, et al. Retinal imaging using commercial broadband optical coherence tomography. Br J Ophthalmol. 2010;94:372e376.

7. Zhang T, Kho AM, Srinivasan VJ. Improving visible light OCT of the human retina with rapid spectral shaping and axial tracking. Biomed Opt Express. 2019;10:2918e2931.

8. Miller DT, Kurokawa K. Cellular-scale imaging of transparent retinal structures and processes using adaptive optics optical coherence tomography. Annu Rev Vis Sci. 2020;6:115e148.

9. Zhang T, Kho AM, Srinivasan VJ. In vivo morphometry of inner plexiform layer (IPL) strati cation in the human retina with visible light optical coherence tomography. Front Cell Neurosci. 2021;15:655096.

10. Lupidi M, Mangoni L, Centini C, et al. Quantitative and qualitative assessments of retinal structure with variable A-scan rate Spectralis OCT: insights into IPL multilaminarity. J Clin Med. 2023;12:2637.