Retina Flashcards
Retina is red because of what compound?
purple rhodopsin
T/F: Retina grays/opacifies about 1 hr after death
True
What is the chief function of rods?
Detecting light and movements
What is the chief function of cones?
Color and form vision
Rods and cones are named based on the appearance of their what structures?
Outer segment
T/F: Retina is is thick centrally and peripherally
False! Retina is THIN centrally and peripherally
T/F: optic disc is devoid of photoreceptors
True. And this creates a blind spot
Macula lutea is yellow because of what pigment?
xanthophyll
T/F: Foveola only contains rods
False! Foveola contains only CONES.
What is the diameter of foveola
0.35mm
What are the functions of pigment epithelial cell layer?
Absorption of light and removal of heat
Restricts stray light; protects receptors from undesirable effects of light
Provides photoreceptors with nutrients/ O2
Reservoirs of useful substances (ex. Vit A)
Provide slow disintegration, a role in phagocytotic activity
Rods are shed or sloughed off when?
In the morning or when dark periods are over.
What is Nyctalopia?
Loss of night vision due to vitamin A deficiency.
T/F: Fovea does not contain any blood vessels.
True
What is the diameter of the fovea?
1-2 mm
What does the ora serrata separate?
Ora serrata separates the neural part of the retinal peripherally from the ciliary body.
How do arteries appear in fundus photograph compared to veins?
Arteries appear thinner and lighter compared to veins which appear wider and darker
What are the four subdivisions of the retina?
- Pigment Epithelial Layer
- Photoreceptor Layer
- Intermediate Cell Layer
- Ganglion Cell Layer
Do pigment epithelial cells undergo mitosis?
No. Pigment epithelial cells of the retina do NOT undergo mitosis
What happens when pigment epithelial cells are dead?
Cells neighbors occupy their places when they are dead.
Each pigment epithelial cell is in contact with how many photoreceptors?
Each pigment epithelium cell is in contact with an average of up to 45 photoreceptors.
T/F: Photoreceptors have a palisade arrangement
True
What is the rate of lamellae formation in rods and where does it take place?
Lamellae formed at a rate of 1-5 per hour at the bottom of the segment
How often can rod lamellae be completely renowned?
1-2 weeks
How long are rods? How thick?
Long (40-60 µm) and about 2 µm thickness
Where is the rhodopsin (photopigment) found in rods?
Found in discs and some extent plasma membrane of rod outer segment
T/F: Rods are very sensitive to light.
True
What pigment is found in Cones?
Iodospin
Why aren’t colors seen during night vision?
Because cones do NOT react to small amounts of light.
When does most of cone shedding occur?
During end of the day (night)
What type of light are cones most sensitive to?
- short λ/ blue
- medium λ/ green
- long λ/ red
What kind of protein is rhodopsin? And what does it contain?
Rhodopsin is an intrinsic membrane protein and it contains vitamin A.
What are the four chemical forms of Vitamin A
- Retinyl ester (storage)
- retinal (Visual transduction)
- retinoid( transport/hormonal)
- retnoic acid (synthesis)
Which two proteins bind vitamin A (in the form of retnoid) while it is being transported?
- retinol binding protein (RBP) inside the cell and
2. prealbumin (PA) in the bloodstream
What are the diatery sources of Vitamin A?
β-carotene (yellow vegetables) Retinyl esters (animal sources)
What does excessive intake of vitamin A cause?
Excessive vitamin A causes increased gluconeogenesis and protein turnover
What are the three cell types found in ganglion cell layer?
Magno cells (9%), parvo cells (80%), konio cells (9%)
How many rods are there?
110-125 million rods
How many cones are there?
6.5 million cones
T/F: central fovea has the highest number of cones.
True
What is the function of the outer limiting membrane?
To hold photoreceptors together
Inner nuclear cell layer of the retina contains cell bodies of which cells?
Bipolar cells Horizontal cells Amacrine cells Interplexiform cells Müeller’s connective fibers
How deep is the ganglion cell layer at the macula? At the periphery?
≈10 cells deep
and about 1 cell layer peripherally
Where is the optic disc located?
Located 3 mm medially to and slightly above the posterior pole
Where is the fovea centralis located?
Fovea centralis is located temporal to and below the posterior pole
What is Henle’s layer?
At the fovea centralis there is retinal thinning → shallow depression in the surface → nerve elements heap (pile up) to form Henle’s layer.
T/F: only rods are found in the foveola.
FALSE. Only cones are found in the foveola!
How does the avascular region of the fovea get nutrition?
- Blood vessels surrounding it and
* from the choroid behind it
Where is ora seratta?
*6mm infront of the equator and 8.5mm behind the limbus.
T/F: The fovea contains blood vesssels.
False. There should be no blood vessels on the fovea.
T/F: pigment epithelial cells of the retina do multiply.
False. There are about 5 million cells in the RPE (pigment epithelial cell layer) and they do NOT multiply.
What kind of cells are found in the RPE (retinal pigment epithelial) layer?
single stratum (layer) of cells attached to the Bruch’s membrane
The cells in the RPE are attached to what structure of the choroid?
Bruch’s membrane
The photoreceptors are held together by what structure of the retina?
external limiting membrane
Which cells transform light into electrical energy by chemical processes
Photoreceptors (cones and rods)
T/F: In rods sensation is the same for all wavelengths of light
True
Explain convergence of impulses from rods.
several rods connect with one bipolar cell-> convergence of signals.
T/F: Cones are shorter than rods?
True
What is the shape of cones at the fovea?
At the fovea, cones are more cylinderical shaped which resemble rods.
In cones the lamellae are attached to which part of the cell?
To the cell membrane.
What is Tay-Sachs?
*Disease is a result of hexaminodase A deficiency
(which normally breaks down gagliosides)
*this leads to an accumulation of GM2 in the retina and ganglion cells degenerate- cherry red spot
*leads to early blindness and death at 3-6yrs old
Breakdown of hexaminodase A deficiency is a characteristic of which disease?
Tay-Sachs.
Viramin A is a fat soluble vitamin. T/F?
True
What does vitamin A deficency cause? Name the three diseases.
Nyctalopia–>Xerophthalmia–>Keratomalacia
Retinal blood supply is mostly from which artery?
Central retinal artery
T/F Capillary network is densest at the macula.
True
