Layers of the Retina Flashcards
Retinal cells are highly organized into 10 layers (outer to inner)
- RPE (supports photoreceptors)
- Photoreceptor
- External limiting membrane
- Outer nuclear layer
- Outer plexiform layer
- Inner nuclear layer
- Inner plexiform layer
- Ganglion cell layer
- Nerve fiber layer
- Internal limiting membrane
*layers 2-10 are considered neural/sensory retina.
How are RPE cells attached to the choiriocapillaris
Through Bruch’s
RPE is outer to ___ and inner to ___
Outer to photoreceptors and inner to choriocapilaris
Subretinal space
Gap between the RPE and the photoreceptors.
How does the RPE and photoreceptors stay close together regardless of the sub retinal space?
They are held in case approximation due to
- Microvilli that extend from the apical surface of RPE cells that envelop the outer segment tips of photoreceptors.
- Interphotoreceptor matrix (IPM) secreted by the RPE cells has adhesive properties.
- IOP due to aqueous humor.
- Presence of vitreous humor (+/-) may or may not keep photoreceptors against RPE
-No gap junctions, tight junctions, or desmosomes here
A common site of neurosensory retinal detachment (Photoreceptors separated from RPE)
Subretinal space- there are no gap or tight junctions, or desmosomes here
Outer vs inner
Outer- choroid/sclera
Inner- vitreous
Photoreceptor layer
-Composed of?
Composed of outer and inner segments of the photoreceptor cells. (outer is touching the RPE and inner is closer to the cilium)
Contains projections of the muller cells that extend between inner segments, and then extend to the outer/external limiting membrane.
Outer limiting membrane (OLM) or external limiting membrane (ELM)
- Located where?
- Composed of what?
Junction between:
photoreceptors: photoreceptors
Photoreceptors: muller cells
Composed of zonula adherens
Outer nuclear layer (ONL)
Composed of photoreceptor cell bodies- they are arranged in different layers due to height.
Generally, cone nuclei lie in a single layer next to the external limiting membrane(more outer, closer to choroid), and rods are arranged in several rows inner to the cone bodies (closer to the vitreous- they are taller)
When you hear “nuclear,” you should think ___
Cell body
Outer plexiform layer (OPL)
What does it contain?
Composed of synapses between
Photoreceptors and bipolar dendrites
Photoreceptor axons and horizontal cell processes
Horizontal cell processes and bipolar dendrites
When you hear “plexiform,” think ___
Synapse
What border is within the OPL?
The middle limiting membrane. It is a border between the inner 2/3 and outer 1/3 retinal blood supply.
Created by the desmosome-like attachments between bipolar dendrites and horizontal cell processes that resemble a discontinuous membrane.
The middle limiting membrane is located where and formed by what
It is located within the outer plexiform layer and is created due to desmosome like attachments between bipolar dendrites and horizontal cell processes. Creates a discontinuous membrane that borders the inner 2/3 and outer 1/3 retinal blood supply.
Inner nuclear layer
Cell body layer. Composed of bipolar, horizontal, amacrine, and muller cell bodies.
Inner plexiform layer
Second synapse layer.
Composed of synapses between:
-bipolar axons to ganglion dendrites and cell bodies
-Bipolar axons to amacrine processes
-Amacrine processes to ganglion dendrites
-Amacrine processes to amacrine processes
Ganglion cell layer
Cell body layer.
Generally a single layer with cells side by side with muller cell processes between them.
Nerve fiber layer
Composed of ganglion cell axons (nerve fiber)
Axons extend from ganglion cell bodies and form bundles as they course parallel to the retinal surface and gather at the optic disc.
Contains 4 bundles of axons- 1. Papilomacular 2 Super temporal 3. Inferior temporal 4. Nasal bundle
Once the nerve fibers reach the optic disc, they turn at a right angle and exit the eye through the lamina crib rosa at the ON.
4 different bundles in the nerve fiber layer
- Papilomacular bundle
- Macular fibers course from the center of the fovea directly to the temporal margin of the optic disc. Comprises more than 90% of all axons in the ON
2/3. Superior and inferior temporal
-Arch around the papillomacular bundle to the super and inferior margins of the optic disc
- Nasal bundle
- Course in a radial pattern directly to the nasal margin of the optic disc.
Once the nerve fibers reach the optic disc, they go where?
They turn at a right angle and exit the eye through the lamina crib rosa at the ON.
Internal limiting membrane or inner limiting membrane (ILM) is composed of what?
Composed of termination of muller cell processes (footplates) covered by a basement membrane. In contact with the vitreous.
What layers of the OCT are hyper reflective?
(Where synapses occur)
Outer RPE/Bruchs RPE interdigitation Cilium (IS/OS junction, or PIL) External limiting membrane Outer plexiform (photoreceptor synapse with BP) Inner plexiform (BP synapse with ganglion) Nerve fiber layer Inner
What layers of the OCT are hypo reflective?
Where cell bodies are located
Outer
Outer segments
Inner segments
Outer nuclear layer (photoreceptor cell bodies)
Inner nuclear layer (bipolar, horizontal, amacrine and muller cell bodies)
Ganglion layer (ganglion cell bodies)
Inner
What is the IS/OS junction, or PIL?
PIL is the photoreceptor integrity line, also known as the cilium.
The PIL is what provides nutrients to the inner segments from the RPE cells and the outer seg. If it isn’t there, photoreceptors will lose function aka integrity.
Integrity
Function
PIL
Photoreceptor integrity line AKA cilium. Sends nutrients from the outer segment to the inner segment.
Superior temporal and inferior temporal bundles are with respect to the
Temporal raphe (horizontal seam between the superior and inferior retinal nerve fiber layer (RNFL))
RPE interdigitation
Microvilli extending from the RPE- hyper reflective layer
