Retina Flashcards
how much of the eye is retina
extends over the posterior 2/3 of globe
what are the boundaries of the retina
internally bound by the vitreous and externally connected to Bruch’s membrane
how many layers thick is the retina
10
what color is a normal retina
reddish because of purple rhodopsin (thin transparent membrane)
what happens to the retina with light exposure
bleaches
when does the retina turn gray/opacify
1 hr after death
what are the two chief retinal functions
detecting light and movement (rods) and color and form vision (cones)
what are rods and cones names based on
the appearance of their outer segments
where is the retina thinest
centrally and peripherally
what is the fundus oculi
the internal background of the eye, orange-red color secondary to choroid and RPE
what does the fundus look like in fair and darker subjects
lighter in fair and darker/grayish fundi
what does the fundus look like in albino patients
you can see the choroidal vessels through the retina and the white scleral tissue
why is the fundus of albino patients transparent
they are almost devoid of pigment (extremely photophobic)
where is the optic nerve located
3mm medially to and slightly above the posterior pole
what is the blind spot
the optic disc is devoid of photoreceptors- its projection into space produces the blind spot
where is the fovea centralis located
temporal to and below the posterior pole (1-2mm diameter)
what is the fovea centralis
retinal thinning produces a shallow depression in the surface where the nerve elements are heaped to form Henle’s layer
what is the foveola
the 0.35mm within the fovea, only has CONES
what is the macula lutea
the yellow spot around the fovea centralis, yellow pigment (xanthophyll) found here
what are the 4 areas of the fovea centralis
foveola, fovea, parafoveal area, and periforveal area
what is the ora serrata
it separates the neural part of the retinal periphery from the ciliary body
where is the ora serrata
8.5mm behind the limbus and 6mm in front of the equator
where is a common spot for retinal detachments
in the ora serrata- the vitreous is firmly attached here
what do the arteries and veins look like in the retina
the arteries are thinner and lighter, veins are wider and darker
are there anastomoses in the retinal arteries and veins
no
what are the 4 subdivision regions of the retina
pigment epithelial layer, photoreceptor layer, intermediate cell layer, ganglion cell layer
what is the pigment epithelial layer (RPE) connected to
Bruch’s membrane
what are the 5 functions of the RPE
- absorption of light and removal of heat
- captures excessive and stray light- projects receptors
- provides nutrients and O2 to photoreceptors
- reservoirs of useful substances (vitamin A)
- phagocytotic activity of shed discs
does the RPE layer have mitosis
no, neighboring cells occupy space after cells die
how many cells is each pigment epithelium cells in contact with
up to 45 photoreceptors
what is the connection between the photoreceptor layer and the RPE
no real connection (only adjacent to each other)
what are photoreceptors
sensory cells: transform light into electrical energy by chemical processes
what is the arrangement of the photoreceptors
palisade arrangement (picket-fence) being held in position by the external limiting membrane
what do rods look like
long (40-60 microns), slender (2 microns)
what is the outer segment contain in a rod
rhodopsin- about 600-1000 loosely stacked disc units (lamellae)
what is the rate of formation for the lamellae in the rod
1-5 per hour at the bottom of the segment
which lamellae get sloughed in a rod
a group of 30 from the top of the segment
when does sloughing occur the rod lamellae
in the morning or after long dark periods
when can rod lamellae be completely renewed
over 1-2 weeks
do rods have a high or low sensitivity to light
a high sensitivity (sensation is the same for all wavelengths of light)
how many rods go to one bipolar cell
several (15-30) producing an impulse convergence
where are the cones more cylindrical shaped
in the fovea-due to packing so many in a small space
what is the cone pigment
iodopsin
what are the outer segment lamellae attached to in cones
the cell membrane
do cones react to large or small amounts of light
large (why colors are not seen during night-dark vision)
when are the discs of the cones shed
periodically and mainly during the end of the day
what are the 3 cone photopigment categories (each having a distinct spectral sensitivity)
short (blue), medium (green), and long (red) wavelengths
what is rhodopsin
an intrinsic membrane protein, found in discs and some extent plasma membrane of rod outer segment
where is rhodopsin more prevalent
in the discs
what is formed after light hits rhodopsin
Bathorohdpsion forms
what is formed following metarhodopsin
all trans retinal and opsin are produced
what are the two steps to regenerate rhodopsin from metarhodopsin
all trans retinal is isomerised to 11-cis retinal isomerase and then opsin combines with 11-cis retinal to make rhodopsin
what is Tay-Sachs ganglioside (GM2)
a genetic retinal disease, where partially degraded gangliosides accumulate in neural, ocular and other tissues
what is Tay-Sachs ganglioside a result of
hexaminodase A deficiency (the enzyme that normally catalyzes the breakdown of ganglioside molecules)
in Tay-Sachs gangliodie, what appears on the retina as a result of the accumulation of GM2 and ganglion cells degenerate
a cherry red spot in the macular region
what symptoms occur with Tay-Sachs ganglioside
blindness occurs early and failure to develop motor/mental capacities (resulting in death age 3-6)
what forms Rhodopsin
11-cis vitamin A aldehyde (retinal) and opsin
what class of lipids does vitamin A belong to
the isoprenoid class
what is the role of retinyl ester
storage
what is the role of retinol
transport and hormone to control certain kinds of protein synthesis
what is the role of retinal
visual transduction
what is the role of retinoic acid
synthesis- formation of glycoproteins and the maturation of epithelial cells (corneal epithelia)
what are the 4 chemical forms of vitamin A
retinyl ester, retinol, retinal, and retinoic acid
what are 2 dietary sources of vitamin A
beta-carotene (yellow vegetables: carrots and sweet potatoes) and retinyl esters (animal sources)
what are both sources of vitamin A converted to in the gut
vitamin A alcohol (retinol), then it is re-esterified and incorporated into chylomicra for liver transport
what two proteins does vitamin A (retinal) bind to before mobilizing
retinol binding protein (RBP) inside the cell and prealbumin (PA) in the bloodstream
after vitamin A (retinal) is bound to two proteins where is it transported to
through the blood stream to its target cells: retina and corneal epithelium
what is the first sign of a vitamin A deficiency
Nyctalopia (loss of night vision)
what is follows nyctalopia
xerophthalmia (dry eyes, hardening of corneal conjunctival epithelium and loss of conjunctival secretions)
what is the last stage of a vitamin A deficiency
keratomalacia (degeneration of the corneal epithelium, could cause corneal perforation
what are some symptoms of vitamin A excess
abdominal pain, blurred vision, drowsiness, headache, irritability, nausea, and vomiting
what are the 2 causes of excess vitamin A
increased gluconeogenesis and protein turnover (converts the protein into glucose)
what type of connection do cones make with bipolar cells
a direct synapse, fewer cones are connected to a single bipolar cell
which type of cell, rods or cones, provide more localized information
cones, they have fewer cells connected to a bipolar cells
how many rods do we have
110-125 million
how many cones do we have
6.5 million
how many rods are in the central fovea
0
how many cones are in the central fovea
147,000 cones/mm2
how many rods are 5-6mm from the fovea
160,000 rods/mm2
how many cones are 10mm from the fovea
4,000 cones/mm2
what is the outer limiting membrane
a support network to hold the photoreceptors together, condensation of cytoplasm (not a real membrane)
what does the outer plexiform layer consist of
photoreceptor axons, synapses with bipolar cell dendrites, and connections between horizontal cells and photoreceptor synapses
what 5 cell bodies are in the inner nuclear layer
bipolar cells, horizontal cells, amacrine cells, interplexiform cells, and mueller’s connective fibers
what is the ganglion cell layer
formed by the bodies of the cells found in the inner nuclear layer
how deep is the ganglion cell layer
about 10 cells deep at the macula and only one cell deep in the periphery
what are the 3 types of ganglion cells
magno cells (motion), parvo cells, and konio cells (blue-yellow)
which ganglion cell is most abundant
parvo cells
what is in the nerve fiber layer
ganglion cell axons- carrying nervous impulses via the optic nerve to the lateral geniculate nucleus
what envelopes the nerve fiber layer fibers
extensions of Mueller’s fibers and astrocytes
what are 2 retinal glial cells
astrocytes and microglia
where are astrocytes found in the retina
the ganglion and nerve fiber layer (short and long projections extending in all directions)
what do the astrocyte cells promote
movement from and to the vascular system (nourishment function)
what are microglia
small connective cells, few present in healthy tissues
what do microglia do
proliferate for phagocytosis where damage is present
what is the main arterial supply to the retina
central retinal artery
what happens to the central retinal artery at the optic disc
the main retinal vessels divide into superior and inferior branches and those divide into nasal and temporal branches
where is the capillary network in the retina
densest near the macula and absent in the fovea (lacking in a small area behind the ora serrata)
what supplies the fovea with blood
diffusion will carry nutrients to the fovea (the choroidal layer also supplies the fovea)
what is the venous supply to the retina
central retinal vein- exits at the optic disc
