Retina (Q3) Flashcards
What does the posterior pole include?
Area of retina bordered by the superior and inferior temporal vasculature and includes the macula and optic nerve head. It is the area evaluated when performing direct ophthalmoscopy
How many microns is a third of a disc diameter? ~0.33 DD = _____
500 microns (know for 2nd year)
What is the range of average optic disc diameters in mm?
1.5mm - 2.2mm
What are the parts of the macula from largest to smallest/outer to inner?
Macula, perifovea, parafovea, fovea, foveola
Which cells are in high number in the parafovea?
Bipolar and ganglion cells
Which part of the macula is ONLY cones?
Foveola
What is the average diameter of the retina from ora to ora?
32mm
Where does the Foveal Avascular Zone receive blood since it is devoid of retinal vessels?
From the choroid
What are the three possible blood supplies to the retina?
Choroid (supplies outer 1/3), central retinal artery (supplies the inner 2/3), and cilioretinal artery (to macular area, seen in 20% of the population)
What are the 10 layers of the retina?
- RPE 2. Photoreceptors 3. External limiting membrane 4. Outer nuclear layer 5. Outer plexiform layer 6. Inner nuclear layer 7. Inner plexiform layer 8. Ganglion cell layer 9. Nerve fiber layer 10. Internal limiting membrane
Which are the first-order neurons in the retina?
Photoreceptors
Which are the second-order neurons in the retina?
Bipolar cells
Which are the third-order neurons in the retina?
Ganglion cells
About how many photoreceptors, bipolar, and ganglion cells are there (each)?
100 million photoreceptors, 36 million bipolar cells, 1 million ganglion cells (retinal pathway is an example of a converging system)
About how many photoreceptors can an RPE cell support?
Each RPE cell interacts with 30-40 photoreceptors
Which of rods or cones are responsible for scotopic and which is responsible for photopic vision?
Rods for scotopic (night vision), cones responsible for photopic (daytime vision)
What is the name of the structure that connects the outer and inner segments of a photoreceptor cell?
Cilium
What are the two regions in the inner segment of a photoreceptor cell?
Myoid and Ellipsoid
What cellular organelles are found in the myoid region of the photoreceptor?
contains ER and Golgi apparatus for protein synthesis
What cellular organelles are found in the ellipsoid region of the photoreceptor?
Contains mitochondria, important for energy for the cell
What are the synaptic terminals of the photoreceptors called for rods, and for cones?
Rods = spherules
Cones = pedicles
What happens to old outer segment discs of the photoreceptor?
Discs are shed throughout the day and phagocytosed by the lysosomes in the RPE cells
About how many millions of cones are there?
4-5 million!
Which type of cone is found less but more consistent in ratio to the other two? S, M, or L?
S, short-wave, blue cones are fewer but have a more constant ratio to the other than M and L to each other have
About how many millions of rods are there?
80-100 million!
Where is the density of rods the greatest?
3mm away from the center of the fovea (rod ring)
Where is the density of cones the greatest?
fovea
Where are photopigments produced and what are the 2 components?
Produced in the inner segment of the photoreceptor, composed of chromophore and opsin
What is the photopigment in rods called?
Rhodopsin
What is the difference between chromophore and opsin?
Chromophore absorbs light and begins process of phototransduction, opsins are responsible for wavelength sensitivity/absorption characteristics and are different for each type of cone
How common are colour deficiencies (what percent of population)?
4.5% of the population has a colour deficiency, most are genetic
Which chromosomes are the genes that code for human opsin found?
The genes for M and L cones are located on the X-chromosome, the genes for S cone are on chromosome 7 and the Rhodopsin genes are located on chromosome 3
Which cone genes developed alongside each other?
M and L cone genes are 98% homogenous. Homology to S cone is only 40% suggesting that the S cone evolved at a different time
What is CHRPE?
Congenital hypertrophy of the RPE, caused by enlarged RPE cells with densely packed melanin granules, can be associated with colon cancer
What are the symptoms of cone dystrophy?
photophobia, difficulty distinguishing colours
Where is the external limiting membrane and what is its function?
Not a true membrane, it is formed between Muller cells and photoreceptors at the level between photoreceptor inner segments and cell bodies. Functions to restrict the movement of large molecules (has zonula adherens)
What are the two synaptic layers of the retina?
Outer plexiform layer and inner plexiform layer
What is the neurotransmitter released from the photoreceptors’ synaptic terminals?
Glutamate
What is the “middle limiting membrane” of the retina?
the OPL, marks the extent of the retinal vasculature, choroid for outer and CRA for inner retina
What are the two capillary networks in the retina and which layers are they found in?
Deep - located in the inner nuclear layer
Superficial - located in the nerve fiber layer
What are exudates and where are they found?
lipid material that leaks from blood vessels, found in the OPL, associated with hypertension, diabetes, hereditary ocular conditions, wet AMD. different from drusen!
What is retinoschisis and where does it occur?
splitting of the retina at the level of the OPL (not an RD)
What cell bodies are found in the inner nuclear layer?
cell bodies of horizontal, bipolar, amacrine, interplexiform, and Muller cells
(also is the location of the deep capillary network)
Which layers of the retina are dot and blot hemorrhages located in?
In the OPL or INL, often associated with uncontrolled diabetes or hypertension, resolve over several months
What is the function of horizontal cells?
single axon and multiple dendrites to carry information horizontally across the retina, synapsing with photoreceptors, bipolar cells, or other horizontal cells in the OPL
What is the physiology of the synapses from horizontal cells?
Depolarize in the dark, provide inhibitory feedback to photoreceptors and inhibitory feed-forward to bipolar cells, “lateral inhibition”, NTs are glutamate or GABA
What is the function of bipolar cells?
To transmit information from the photoreceptors to the ganglion cells (done with graded potentials)
How many types of bipolar cells are there and how do they differ?
11 types, depends on size, synaptic connection and communication. However, they all have the same function, NT (glutamate), and receptive fields (either ON or OFF)
What is the difference between diffuse and midget bipolar cells?
based on the extent of the dendrites, diffuse has a wide range of influence contacting multiple cones (5 in center, 10-15 in periphery) and converges information, midget has a small range of influence contacting only a single cone in the fovea or 2-3 cones in the periphery.
What is the difference between flat and invaginating bipolar cells?
based on the dendrites placement on the cone pedicle, flat are superficial contact while invaginating are located within the cone pedicle
What are the characteristics of the rod bipolar cells?
the ONLY bipolar cells that contact rods, not found in the foveola, rarely synapse directly with ganglion cells (will synapse with amacrine cells), a single rod bipolar cell can contact 15-20 rods in central retina or up to 80 rods in the peripheral retina
How are blue cone bipolar cells different?
connect widely spaced blue cones rather than neighboring cones
Which classification type of bipolar cell depolarizes in the light and which depolarizes in the dark?
ON-cells depolarize in the light
OFF-cells depolarize in the dark
Which cell in the retina carries information both vertically and horizontally, and also produces action potentials?
Amacrine cells
How many kinds of amacrine cells are there, including stratified and diffuse? (not asking groups)
30-40 kinds
The most well known amacrine cell is AII, where does it synapse?
AII is found in the rod pathway connecting rod bipolar cells (synapse with up to 80) to ganglion cells
Which neurotransmitters are released by amacrine cells?
GABA and glycine (amacrine cells are inhibitory, feedback to bipolar cells and inhibitory feed-forward to ganglion cells)
What is known about the interplexiform cells?
have large cells bodies in the INL with processes in the OPL and IPL, relaying information laterally
How thick is the ganglion cell layer?
1-2 cells thick in the retina, with 4-7 cell layers thick in the macula, (less near the ora serrata)
Approximately 18 different kinds of ganglion cells fall into one of two broad categories:
-Parvocellular (P-cells)
-Magnocellular (M-cells/parasol ganglion cells)
Which layers of the LGN do P-cells vs. M-cells project information to?
P-cells project to layers 3,4,5,6
M-cells project to layer 1,2
Which types of information are the P-cells vs. the M-cells sensitive to?
P-cells are sensitive to colour and fine detail (‘what’ pathway)
M-cells are sensitive to dim changes in illumination and motion (‘where’ pathway) broader information
What are the two types of P-cells?
- P1 ganglion (midget) cells, most common, only synapses with 1 midget bipolar cell which only goes to 1 cone
- P2 ganglion cells are larger and synapse with multiple bipolar cells
Do ganglion cells produce action potentials or graded potentials?
Action potentials!
Where is the nerve fiber layer the thickest and where is it not present?
NFL is thickest near the ONH and not present in the fovea
Which capillary network are flame-shaped hemorrhages associated with and which layer of the retina is this network found in?
Superficial capillary network found in the nerve fiber layer