Fig. 17.

The reflective structure of the retina showing the two bright reflections especially from the cone photoreceptors that are the basis for cellular interferometry.

(a) A diagram depicting the major layers of the neural retina, consisting of the inner limiting membrane (ILM), nerve fiber layer (NFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), external limiting membrane (ELM), the inner segments (IS) and outer segments (OS) (which make up the photoreceptor layer), the connecting cilia (CC) and posterior tip (PT) layers (which bound the outer segment), the retinal pigment epithelium (RPE), and the choroid (CH). (b) An AO-OCT B-scan (log intensity), showing a cross-section of the full retinal thickness, aligned with the layers depicted in (a), and an enlarged view (linear intensity) of the cone outer segments. While OCT images are typically shown in log intensity, the linear intensity view of the outer segments demonstrates vividly that the bulk of the cone reflection originates at the CC and PT layers: the bright, patterned reflections at the CC and PT layers are the most visible structures in the linear intensity image; their peak intensity is more than two orders of magnitude greater than the average intensity of all other layers in the image. Each distinct reflection in the pattern represents a single cone cell. (c) A model of light propagation through the OS. Two bright reflections (ψ₁ and ψ₂) originate from the CC and PT layers, creating a biological interferometer in the retina that is sensitive to small (≪ λ) changes in the outer segment length L whenever the temporal coherence length of the illumination source L^c is longer than L. From Jonnal et al. (2010)