Biochemistry of Vision Flashcards
retina
ora serrata - anterior edge
nonsensory retinal pigment
epithelium -can inject
sensory retina
sensory retina
macula lutea
fovea centralis
optic disk
anatomic axis
doesn’t line up
visual axis
to fovea centralis
- most acute vision
- image directly projected here
macula lutea
surrounds fovea centralis
optic disk
where optic nerve arises
-retinal vessels present
cell types of retina
neurons
retinal pigment epithelium
neuron support cells
photoreceptor cells
rods and cones
neurons of retina
outer - photoreceptors
- interneurons
- retinal ganglion cells
retinal pigment epithelial cells
outermost layer
-separate retina from choroid
mueller cells
support cells from inner to outer membrane of retina
choreocapillaris
closest choroid to retina
inner portions of retina
too far for diffusion from choroid
-so instead get blood from retinal blood vessels
slide of retina
look for cell nuclei
-easy to see different layers
ganglion cell layer
larger cells
layers in order of signal transduction
pigment epithelial cells photoreceptor cells outer limiting membrane outer nuclear layer outer plexiform layer inner nuclear layer inner plexiform layer ganglion cell layer optic nerve fibers inner limiting membrane
photoreceptor cell segments
inner and outer
-both in exterior of eye
inner segment of photoreceptor
rich in organelles
outer segment of photoreceptors
flat membranous disks with photopigment
-continuous turnover - move exteriorly
rods
light of differing intensity
around periphery of retina
rhodopsin
cones
blue, green, red
COLOR
fovea
contain iodopsin
rhodopsin
in rods
iodopsin
in cones
internal photoreceptor matrix
important
- provides nutrition to photoreceptor and remove waste
- including shed membranous disks
cycling proteins - interstitial retinal binding protein
interstitial retinal binding protein
transports retinol to RPE and retinal to the photoreceptor
RPE
retinal pigment epithelium
- contains melanin granules
- phagocytose shed disks
- retinol re-isomerization enzyme
11-cis retinal to retinol
rods end in?
end in rod sperule
- dendrites of bipolar cells
- neurites of horizontal cells
cones end in
cone pedicle
-dendrites of bipolar cells
neurites of horizontal cells
neurite
ether dendrite or axon?
proteins in photoreceptor
photopsin
- cones iodopsins
- rods rhodopsin
chromophore
11-cis retinal
-combine with the photopsin to form the iodopsin
red, green, blue stimulated together
seen as white light
photobleaching
photopigment absorbs photon of light and changes confirmation
photopigment contains protein and 11-cis retinal
- change from cis to trans
- also changes the opsin it is associated with
acts as GPCR
photopigment
acts as GPCR when stimulated
-GMP from cGMP
reduced cGMP levels
high cGMP
photoreceptor off
- activates sodium channels
- dark = open sodium channels
decreased cGMP
close sodium channels
due to photoreceptor activation
visual cycle
bleaching and cycling between retinoids
all-trans-retinol
converted to all trans-retinal in RPE
-which can be cycled
leber congenital amaurosis type 2
group of mutations in RPE65
- isomerohydrolase
- converts all trans retinol to 11 cis retinal
in RPE
loss of vision results
autosomal recessive
bipolar cells
receive impulse from photoreceptor cell
-rod and cone varieties
diffuse cone bipolar
input from multiple cells
midget cone bipolar
input from single cell
only in cones
thought to be involved in visual acuity (1:1 ratio)
diffuse ganglion cells
contact with several bipolar cells
midget ganglion cells
contact with single bipolar cells
**possibly better acuity
association neurons
integrate signals
- amacrine cells - end ??
- horizontal cells - end on cone pedicles and rod spherules
mueller cells
span retina
microglia
present in all layers
visual axis of cornea
a fovea
central depression
fovea centralis
surrounded by macula
flattening of cells at an angle to allow more light in**
greatest visual discretion
-mostly cone photoreceptors
low light vision here = bad
macular degeneration
breakdown of macula
macular edema
inflammation at macula
not maculitis
inflammation optic disk
pappil edema
optic nerve
convergence of axons of retinal ganglion cells
myelination begins at optic disk
blind spot
absence of photoreceptors at the optic nerve
-only axons
avascular structure
fovea centralis
-don’t want to impede the movement of light
thickness diminished - can get nutrients from choroid
vascular structure
optic disk
choroid
outer retinal blood supply
central retinal artery
rises from optic nerve head
-maintenance of inner retina
branches to three layers of capillaries
-run posterior to inner limiting membrane, within the nerve fiber layer
photoreceptors and horizontal cells
NO blood from central retinal atery
–they get blood from choroid
retinal detachment
photoreceptor layer from RPE layer
-hemorrhage in that area
between brooks membrane and RPE
decreased diffusion of outer segments
-lose vision
retinal tear
vitreous can leak in and cause retinal detachment
diabetic retinopathy
complication of diabetes
-after 15-20 years
pathology of diabetic retinopathy
microaneurysms cotton-wool spots - loss of vasculature retinal veins - dilated and tortuous retinal arteries - white / nonperfused selective loss of pericytes - from retinal capillaries apoptosis of capillary endothelial cells
preproliferative phase
increased size and number of intraretinal hemorrhages
- no vision loss
- vision loss due to macular edema
proliferative phase
formation of new blood vessels
-can protrude into vitreous
- clouded vision
- detached retina
can extend to other structures of eye
fundoscopy
opthalmoscopy
-for examining retina
requires dilation of pupil
- to see better picture of entire retina
non-proliferative DR
exudates and hemorrhage
tortuous arteries
VEG-F signaling
proliferative DR
with NEOVASCULARIZATION
tufts of arteries - new growth
larger hemorrhaging
fluorescein angiography
dye into vein in patients arm
-retinal photograph captures fluorescence
can visualize hemorrhage and neovascularization
**see blood supply
allows earlier intervention
optical coherence tomography
used to create cross section of retina
-retinal thickness increases in DR and macular edema
Tx for non-proliferative
blood glucose control
blood pressure control
diastolic BP
may be better predictor of progression
photocoagulation
possible in retina due to presence of absorptive pigment epithelial cell layer
panretinal
for proliferative DR
-across large diameter
focal laser
for non-proliferative DR
-directed to microvascular events
vitrectomy
removal of vitreous humor
can be physical removal or enzymatic
pars plana
area for injecting eye
between retina and ciliary body
glucocorticoid injections
reduce neovascularization
complication - increased IOP
VEG-F inhibitor
to stop vascular growth
primary
no known cause
or congenital/genetic
corneo-irideal angle
obstruction - closed angle glaucoma
open angle glaucoma
no angle closure
-increased IOP
primary - congenital
secondary - particulate matter, episcleral venous pressure
tonometry
measure pressure to depress cornea
slit-lamp examination
low power microscope with high intensity, focused light
examine cornea, iris, lens, cornea, extraocular tissues
iridocorneal angle measure?
with gonioscope lens
large bright space in optic disk
decreased retinal ganglion cells
cup-to-disk ratio
rim - axons
cup - central retinal a and v
whitening of rim
death of retinal ganglion cells
margin changes of rim
death of retinal ganglion cells or inflammation
cup diameter changes
horizontal diameter should be less than half horizontal diameter of disk
1:2 ratio
loss of RGC axons, signs of optic cupping
Tx of optic cupping
increase aqueous outflow
-decreased aqueous production
laser trabeculoplasty
trabeculectomy
drainage of aqueous
trabecular meshwork > canal of schlemme
angle closure glaucoma
primary - anatomical predisposition
-pupillary block
secondary - inflammation, neovascular, contraction of tissue
exam questions
no image identification
-be able to understand the results of an image
