Retina Fundamentals Flashcards
The edge of the macula is defined as:
having 2 or more ganglion cell layers, and eventually becomes up to 10 layers at the fovea/foveola
Foveola
smaller than the fovea “la” because it is diminutive. Foveola is no rods, just cones. Beyond that, just red-green cones tightly packed.
Composition of the fovea
mainly cones, but parafovea has some rods. It is about 4 mm temporal to optic disc and 0.8 mm inferior to disc
Sizes within the macula
fovea is 1.5 mm diameter, foveola is 0.3 mm. umbo is smaller, just .15 mm. Parafovea is 2.5 mm and the perifovea (whole macula) total is 5.5 mm
Layers of the retina:
anatomically, the retina is a neuro-sensory tissue, so think of it as a neuro-sensory sandwich. Neuro part (GCL and RNFL) on top and sensory part (photoreceptors) on the bottom. In between are plexiform and nuclear layers. The limiting membranes—only one (ILM) is a true membrane, made of the footplate of the muller cells which run through the entire retina. The ELM is just what it looks like when the muller cells attach to the photoreceptors. Just appears histologically and on OCT
Anatomy of layers of the retina from anterior to posterior:
Anatomy of layers of the retina from anterior to posterior:
RNFL
is the beginning of the optic nerve, so defects in the RNFL can give you an APD, for example retinal artery occlusions will cause thinning/ischemia of the NFL which relies on superficial vascular supply in contrast with the outer retina which depends on deep vascular supply (like the choroid). Similarly, optic atrophies can cause observable RNFL loss/thinning on OCT
Inner plexiform layer
Mnemonic is In a pink BAG Bipolar cells, amacrine cells, and ganglion cells.
o Ganglion cells make RNFL, bipolar cells carry information from the photoreceptors up to the ganglion cells. Amacrine cells help with image processing, so can modulate the signals between cones and rods and help with line/contrast detection.
Inner nuclear layer
where the nuclei/cell bodies of the cells identified in the IPL live. Pneumonic for cells in the INL: Where Bob Muller Hides Away: Bipolar cells, Muller Cells, Horizontal cells, Amacrine cells. If you want to think about it anatomically, if you go up a layer to the IPL you have the BAG cells. You know the ganglion cells live in the ganglion cell layer, so the bipolar cells and amacrine cells must live here in the INL
Outer plexiform layer
Also called Henle’s layer. Runs obliquely, comes at an angle and splays like a fan. This is why on FA you get a petaloid pattern when there is CME, because the fluid follows along those oblique fibers in the outer plexiform layer
Outer nuclear layer
three cell types. Pneumonic is BPH (think when you have BPH it is hard to pee OUT) bipolar cells, photoreceptor cell bodies, and horizontal cells
External limiting membrane
also called the outer limiting membrane. Where the muller cells meet the photoreceptors. One end of the muller cells makes the ILM and the other end makes the XLM. So they span the entire retina
Photoreceptors
crisp looking line just beneath the other layers on OCT. On OCT 3 segments that can be considered the photoreceptors. IS/OS junction is below the XLM. Also called the ellipsoid zone (the ellipsoid part of the inner segments). Below that is the outer segment tips and then the bright band below that is the interdigitation zone where the outer segments interdigitate with the RPE
RPE
Number of fundamental functions, including absorption of light, (lutein and xanthine does that too); phagocytosis of outer segments; forms the blood-ocular barrier, maintains electrical gradient along the subretinal space, keeps the retina attached. (EOG measures electrical activity across the RPE, as it has an electric potential).
Choroid
3 layers— from inside to outside is: choriocapillaris is the smaller vascular network, then you have the deep choroid, made up of two other layers—sattler and haller’s layer.
