In vivo Morphometry of Inner Plexiform Layer (IPL) Stratification in the Human Retina With Visible Light Optical Coherence Tomography.

Tingwei Zhang,Vivek J Srinivasan,Aaron M Kho

doi:10.3389/fncel.2021.655096

Abstract

From the bipolar cells to higher brain visual centers, signals in the vertebrate visual system are transmitted along parallel on and off pathways. These two pathways are spatially segregated along the depth axis of the retina. Yet, to our knowledge, there is no way to directly assess this anatomical stratification in vivo. Here, employing ultrahigh resolution visible light Optical Coherence Tomography (OCT) imaging in humans, we report a stereotyped reflectivity pattern of the inner plexiform layer (IPL) that parallels IPL stratification. We characterize the topography of this reflectivity pattern non-invasively in a cohort of normal, young adult human subjects. This proposed correlate of IPL stratification is accessible through non-invasive ocular imaging in living humans. Topographic variations should be carefully considered when designing studies in development or diseases of the visual system.

Highlights

The retina transmits and filters light-evoked signals from the two-dimensional photoreceptor mosaic to the output ganglion cells that relay visual signals to the brain
Each synaptic layer is further stratified; the outer plexiform layer (OPL) is divided into rod and cone synapses (Kolb, 1977), while the inner plexiform layer (IPL) is divided into ON and OFF bipolar cell axon terminations, which give rise to ON and OFF channels (Famiglietti and Kolb, 1976; Nelson et al, 1978) that nominally respond to light increments and decrements, respectively
We find that IPL lamination was quantifiable in all eyes where the IPL could be visualized by our visible light Optical Coherence Tomography (OCT) prototype

Summary

Introduction

The retina transmits and filters light-evoked signals from the two-dimensional photoreceptor mosaic to the output ganglion cells that relay visual signals to the brain. The OPL contains synapses between the rod and cone photoreceptors and bipolar cells, with lateral interactions provided by horizontal cells. The IPL contains synapses between bipolar cells, amacrine cells, and the output ganglion cells. Each synaptic layer is further stratified; the OPL is divided into rod and cone synapses (Kolb, 1977), while the IPL is divided into ON (sublamina B) and OFF (sublamina A) bipolar cell axon terminations, which give rise to ON and OFF channels (Famiglietti and Kolb, 1976; Nelson et al, 1978) that nominally respond to light increments and decrements, respectively. The IPL is often further divided into 5 strata of approximately equal thickness, with the two innermost strata

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Conclusion