Ocular Anatomy 10 Retina Flashcards
What is the thickness of the retina? Where is it thinnes?
0.56mm near the optic disc
0.1mm at the ora serrata
Thinnest at the fovea
What are the contacts of the retina
Outer surface in contact with Bruch’s membrane of the choroid
Inner surface in contact with the vitreous body
Antioerly retina becomes continuous with the pigmented and non-pigmented columnar cell layers o fthe ciliary body
What is the ora serrata?
Anterior edge, termination of the retina - insertion of the medial rectus muscle medially and lateral rectus laterally
What are the layers of the retina?
From inside to out:
Inner limiting membrane (ILM) form by amalgamation of inner foot process of Muller cells
Nerve fibre layer
Ganglion cell layer
Inner plexiform layer
Inner nuclear layer
Outer plexiform layer
Outer nuclear layer
External limiting membrane (ELM) formed by amalgamation of the outer foot processes of Muller cells
Photoreceptor layer
Retinal pigment epithelium (RPE) layer
ILM NF G IP IN OP ON ELM P RPE
IN GO NIP IN HOP ON EPR
What forms the ILM and ELM
ILM inner foot processes of Muller cells
ELM outer foot processes of Muller cells
Muller cells are the main neuroglial cell of the retina - derived from neuroectoderm
Arranged radially
How does the retina heal?
Muller cells nad astrocytes form fibroglial scars when there is an insult to the retina
Gliosis
What is the ganglion cell layer?
Bodies of ganglion cells
These are last retinal integrator of information before leaving via the nerve fibres in the NF layer
What are types of ganglion cells
Parasol ganglion cells (M-cells)
Magnocellular layer - project to the lateral geniculate nucleus integrate to from a large receptive field - several photoreceptors
Midget ganglion cells (P-cells)
Parvocellular layer
Prject into lateral geniculate nucleus and make connections with one amacrine and one midget bipolar cells.
Information sent thought this system from a single cone - more detailed info.
More common near the fovea.
Nerve fibres ensheathed by glial cells and myelinated only after exiting the globe.
What is the characteristic features of the plexiform layers
Absence or distinct reduction of cell bodies.
Nerve axons, cell processes make up most
Inner plexiform layer consists of
Processes of bipolar, amacrinse and ganglion cells
Communicates information between inner nuclear layer and ganglion cell layer
Outer plexiform layer contains photoreceptor and bipolar axons - communication between outer and inner nuclear layers
What does the inner nuclear layer contain?
Cell bodies of bipolar, amacine, horizontal and Muller cells
What are bipolar cell funcitons?
Connect in radial fashion - from photoreceptor to synapse with ganglion cells
Rod bipolar cells connect several rod cells to one to four ganglion cells
Flat bipolar cells - connect many cone cells to many ganglion cells
Midget bipolar cells - connect a single cone cells with a single midget ganglion cell
What are amacrine cells?
Connect amacrine to ganglion and ganglion to ganglion cells
Modulate photoreceptor signals by their neurotransmitter contant
What are horizontal cells?
Multipolar cells with one long and several short processes which run both horizontally and parallel with retinal surface
Release GABA in response to stimulation by photorecetors. This inhibits the activity of bipolar cells, increasing contrast and spatial resolution
What are Muller cells
Long narrow, pale staining cells that have long processes that run almost entire thickness of neural retina.
Form integral part of ILM and ELM
Make extensive contacts with blood vessels in the retina, forming part of the blood ocular barrier
What does the outer nuclear layer contain?
Contains the nuclei of photoreceptors - separated by their photoreceptor bodies by the ELM
What are the two types of photoreceptors for?
Rods for vision in dim light and give black and white images
Cones for bright light and resolve fine details and colour vision
How many rods and cones are there in the retina?
120 milllion rods
No rods at fovea
Maximum density at juxtafoveal zone - 160,000 cells/mm2
6-7 million cones, concentrated at the fovea
160,000 cells/mm2
What is the structure of rod cells?
Slender, long (100-120um)
Outer segment is photoreceptor and contains photosensitive pigment rhodopsin
Contains 600-1000 membrane bound discs stacked like coins
Connecting stalk joins outer segment to cell body.
Ellipsoid area next to connecting stalk contains basal body with mitochondria
Myoid segment toward vitreous contains ER, ribosomes, Golgi
What is the structure of cone cells?
Long, selnder (65-75um)
Outer segment is conical and wider
What is the size of the macula? where is it located?
What is the size of the fovea?
4.5mm (three disc diameters
3mm lateral to optic disc
Area in which ganglion cell layer in more than one cell thick
Fovea measures 1.5mm
Most dense area of cone cells
Absent ganglion cell layer and a receptor layer composed entirely of cones
Significance of foveal avascular zone?
500um across
Area must be avoided by laser treatment
What is the retinal pigment epithelium
Hexagonal cells that extend from margin of the optic nerve to the ora serata anteriorly
Basal end of each cell is infolded and rests on Bruch’s membrane of the choroid
Apical ends possess microvilli from 5 to 7 um long
Basal regions joined by zonula occludens surround the cell and join them tightly, isolating the retina from teh systemic ciruclation.
Apical microvilli erode tips of photorecptors and phagocytose the debris.
Cyclical over 24h
Form lipofuscin granules
What is the blood supply to the retina?
CRA - first branch of ophthalmic artery
Where does the retina receive nutrients?
Outer plexiform layer and peripheral from choroidal circulation by diffusion
Inner 2/3 from the CRA and its tributaries
Where does the CRA run?
Runs forward adherent to dural sheath of optic nerve, enters inferior and medial to optic nerve pierces dural sheath 12mm behind globe.
TRavels through subarachnoid space and gives off small miningeal branches that supply pial sheath of optic nerve.
End artery
Runs In the nerve fibre layer with four branches supplying each quadrant of the retina.
Why is macula function presenved in some CRAO
Small anastomoses occur between branches of the posterior ciliary arteries and the CRA
Occasionally a larger connection the cilioretinal artery (from posteroir ciliary artery) exists in approx 20% of people
What maintains the blood reitnal barrier
Zonula occludentes between non-fenestrated retinal blood vessels and between the pigment epithelial cells of the reitina
What is the path of the CRV? Where does it drain?
Tributaries that accompany arteries
Diameter is a third to quarter greater than arteries
Veins leave eye through lamina cribrosa with CRA
Drain into cavernous sinus or superior ophthalmic vein
