Block 11 Flashcards
Monolayer of pigmented cells between choriocapillaris and outer segment of PR
RPE
Apical membrane of RPE faces which retinal layer
PR outer segments
General light absorption occurs where on the retina
Melanin in RPE
Blue light absorption is supplemented by what in the PRs
Lutein and zeaxanthin
The outer retina is exposed to what kind of environment
Oxygen rich
What layer of the retina creates a line of defense against oxidative damage
RPE
RPE contains high amounts of superoxide disputable and catalase
Enzymatic antioxidants
RPE accumulates lutein and zeaxanthin, ascorbate, alpha-tocopherol and beta-carotene
Nonenzymatic antioxidants
The RPE transports nutrients and metabolic end products between what 2 layers
PR and choriocapillaris
The transport of water by PR is driven by what
Active transport of Cl from retina to blood
Bull’s eye shaped lesion
Best’s vitelliform macular degeneration
Best’s vitelliform macular degeneration involves a reduction in transport of what
Reduction in epithelial Cl transport
The transport of lactic acid requires what
A tight regulation of the intracellular pH
What glucose transporters does the RPE containe
GLUT1 and GLUT3
Where does all-trans-retinal reduction to all-trans-retinol occur
PRs
Where does reisomerization of all-trans-retinol to 11-cis-retinal occur
RPE
Mutations in the genes of the visual cycle can cause what
Retinitis pigmentosa
Stargardt disease
Which is inherited, retinitis pigmentosa or stargardt disease
Retinitis pigmentosa
Phagocytosis is under what kind of control
Circadian
Every RPE cells faces how man PR in the fovea
23
How often is a whole outer segment of PR renewed
Every 11 days
Inability of the RPE to phagocytosis PR outer segment
Retinitis pigmentosa
A defect of RPE pR phagocytosis may also cause retinal degeneration in what patients
Usher type 1B patients
What 2 factors stabilize the endothelium of choriocapillaris
PEDF and VEGF
Which factor inhibits endothelial cell proliferation
PEDF
Which factor prevents endothelial cell apoptosis
VEGF
Factors that are essential for maintenance of the structural integrity of retina
TIMP1 and TIMP3
The most severe complication in age-related macular degeneration
Choroidal neovascularization
RPE cells secreted VEGF at a higher rate compared with RPE cells from eyes without neovascularization
Choroidal neovascularization
Tight junction between retinal pigment epithelium
Retina-blood barrier
Apical side of RPE toward
PR
Basolateral side of RPE faces
Choriocapillaris
Light detection by PR
Photon absorption by visual pigment on the discs of the outer segment
Photoreception
Visible light spectrum
400-700 nm
Dim light
Scotopic
Peripheral retina
Scotopic
Color
Photopic
Central retina
Photopic
Motion
Scotopic
Detail
Photopic
Which PR in scotopic
Rods
Which PR in photopic
Cones
Which PR are more sensitive
Rods
Which PR has a higher sensitivity to rapidly changing stimuli
Cones
Are there more rods or cones
Rods
Which are in the fovea
Cones
Peak absorption of rods
500-510 nm
Which PR converge to increase sensitivity
Rods
Which cones are in the fovea
Green (M) and red (L)
Unstable pigments that undergo a chemical change wen they absorb light
Photopigment
Opsin + 11-cis-retinal
Rhodopsin
Erythrolabe
Absorption max for red L cones
Chlorolabe
Absorption max for green M cones
Cyanolabe
Absorption max for blue S cones
Transformation of light into electrical and chemical signals that produces the perception of light
Phototransduction
Important channel in biochemical cascade
CNG channel (cGMP caged cation channel)
What does the CNG channel control
Na, K and Ca into the cell
In the dark, what is the RMP of rods
-50 mV
1st step in biochemical cascade
Photoisomerization of rhodopsin
Reduction of all-trans-retinal into all-trans-retinol occurs in
PR
Reisomerization of all-trans-retinol into 11-cis-retinal occurs in
RPE
The G protein involved in the biochemical cascade
Transducin
If it is GTP binding the the G protein
On
If it is GDP binding the the G protein
Off
Step 2 in the biochemical cascade
G protein activation
Step 3 in biochemical cascade
PDE6 activation
Activated PDE6 converts what
cGMP into GMP
How does PDE degrade cGMP
By hydrolyzing cGMP into 5’-GMP
Step 4 in biochemical cascade
Channel closing (CNG channel)
Opening of the CNG channels puts the PR at what
Resting dark-adapted state
Communication of rods with bipolar cells uses what NT
Glutamate
When there is light, is there more or less glutamate
Less glutamate released
Key molecule of biochemical cascade to keep CNG channel open
cGMP
Major energy producing pathways in the retina
Glycolysis
TCA (need O2)
Electron transport (need O2)
Which glucose transporter is used in the retina
GLUT3
When is lactic acid produced in the largest quantities
Sleep or condition with low oxygen levels
How does ascorbic acid protect the retina and lens
Blocks UV
Scavenges free radicals
Reduces O2 damage during inflammation
Compound that can protect the eye when endotoxin is exposed to the patient
Ascorbic acid/vitamin c
Aqueous glucose level is what percent of serum glucose level
80%
Vitreous to serum ratio of ascorbic acid
9:1
Junction between 2 nerve cells, consisting of a minute gap across which impulses pass by diffusion of a NT
Synapse
Excitatory NT in retina
Glutamate
Inhibitory NT in retina
GABA and glycine
More negative than RMP
Hyperpolarization
Less negative than RMP
Depolarization
In which layer of the retina do the horizontal cells provide lateral interactions
OPL
Bipolar cells transfer the light signals into which layer and onto what cells
IPL; amacrine and GC
Which cells transmit the signals to the visual centers of the brain
GCs
Which NT do cones use
Glutamate
Level of glutamate in the dark
High
Off cone bipolar and horizontal cells are _____ by light
Hyperpolarized
ON cone bipolar cells are _____ by light
Depolarizer
Off cone bipolar cells transfer signals onto
OFF GCs
on cone bipolar cells transfer signal onto
ON GCs
One cone connected to a midget bipolar cells connected to a midget ganglion cell
Midget system
NT in rods
Glutamate
Only one type of rod bipolar cell
ON rod bipolar cell
On rod bipolar cells are _____ by light
Depolarized
Classic rod pathway
Rods —> ON rod bipolar cells depolarized —> amacrine cells depolarized
- glutamate: ON cone bipolar cells —> ON GCs
- glycine : OFF cone bipolar cells —> OFF GCs
Glutamatergic neurons
Rods, cones, bipolar cells and most GCs
GABAergic and glycinergic neurons
Horizontal cells and most amacrine cells
Aging changes in the retina: nerve fibers within the ON
Decrease
Aging changes in the retina: optic cup diameter
Increases
Aging changes in the retina: ILM
Thickens
Aging changes in the retina: foveal reflex
Dimmer (bc of the thickened ILM)
Aging changes in the retina: total number of RPE cells
Decrease
Aging changes in the retina: lipofusin within RPE cells
Increases (drusen increases)
Aging changes in the retina: atrophy
Increases
Age-related retinal atrophy: Pigmentation in RPE/choroid decreases (can see normally hidden choroidal vessels)
Tigroid fundus
Age related retinal atrophy: peripheral RPE degeneration
Reticular degeneration
Which type of cells play a role in transmitting cones signal to GC
Cone bipolar
Which type of cells play a role in transmitting rod signal to GC
Rod bipolar and amacrine cells
What change does ON bipolar cells have with light
Depolarized
NT that bipolar cells have
Glutamate
When the center of a GCs receptive field is exposed to light, which type of GC is stimulated
ON center GC
A transparent, passive structure in the eye
Lens
Does the lens grow throughout life
Yes
Does the lens shed cells as it grows
No
2/3 of the lens is composed of what
Water
1/3 of the lens is composed of what
Protein
Water, protein and small amounts of other components contribute to the need to what
Tightly regulate energy metabolism that predominantly involves glucose metabolism
Most active energy metabolism in the lens (70%)
Anaerobic glycolysis
What energy path is secondary producing NADPH and is 5-10% of the lens energy
HMP Shunt
The rest of the energy (outside of anaerobic glycolysis and HMP shunt) is derived from
Metabolism of lactic acid and glucose in lens epithelium (TCA and ETC)
The 2 dominant source of energy in the lens
Anaerobic glycolysis and HMP shunt
Transport of glucose among cells is accomplished via
Gap junctions
How does the lens get glucose since it has no blood supply
From posterior or anterior surface connecting with other mediums (ex: aqueous humor)
Glucose is takin into cells via
Facilitated transport
How does the lens rid of waste
Via diffusion to aqueous and then to the blood
The epithelial cells are located where in the lens
Anterior pole
What do the epithelial cells of the lens generate
The secondary fibers in the cortex
Which surface of the lens has an upside down y suture
Posterior
What happens to sutures as we age
They get more branches (up to 12)
How much of the total power of the eye is the lens
1/3 (15D)
2/3 of the lens is composed of
Water
1/3 of the lens is composed of
Proteins
3 types of proteins in the lens
Water soluble (crystallins) Urea soluble (crystallins and cytoskeletal) Insoluble (membrane proteins)
What is the main water soluble protein in the lens
Alpha crystallins
90 of the proteins in the lens
Crystallins (water soluble)
What proteins helps keep the lens transparent and give it a higher refractive index
Alpha crystallins
Molecular chaperon of the lens
Alpha crystalline
Where is the refractive index higher in the lens, nucleus or cortex
Nucleus
How is water pumped out of the lens
From anterior surface through Na/K pump
How is water pulled into the lens
From the back surface through osmotic pressure
Where does mitosis of secondary fiber cells of the lens occurs
Germinative zone of anterior lens epithelium
Where do lens fibers migrate after mitosis
Through transition zone and into the equator (elongation begins)
Primary protector against oxidative damage in the lens
Glutathione
Is ascorbic acid highe rin lens or aqueous
Lens
Hofstetter’s formula solves what
How much accommodation someone has left due to their age
Hofstetter’s formula
15-1/4(age)
Type of cataract: decline of glutathione making fibers susceptible to oxidative damages
Nuclear cataract
Type of cataract: fibers lose organelles and gain yellow-brown pigment
Nuclear cataract
Type of cataract: decrease in glutathione activity, increase in Ca, Na and water
Cortical cataract
Type of cataract: epithelial cells migrate from equatorial region and accumulate at posterior pole
Posterior subcapsular cataract
How much does the lens thicken each year
.22mm per year
Which surface of the lens increases
Anterior
Does the radius of curvature of the lens increase or decrease with age
Decrease
Which way does the lens move with age
Anteriorly
Type of cataract: increase in sorbitol production - increase water uptake - lens swell - depletion of NADPH and cant reduce free radicals - protein polymerization
Diabetic cataract
Unusual changes in Rx may indicate
Uncontrolled diabetes
Changes in osmolarity of lens causes changes in
Thickness
Radius of curvature
Rx
What type of light does the lens absorb to protect the retina
UV
Type of protein does the lens contain the most
Crystallins
Where does Na/K pump located to help pump out water
Anterior epithelium
What is the driving force of water entering the lens from the back
Osmotic pressure
Which part is responsible for the formation of secondary lens fibers
Anterior epithelium
What type of changes in the lens are caused by accumulation of sorbitol
Cataract
Rx changes
Single pigmented epithelium of retina
RPE
Help outer retina get nutrition and remove waste
RPE
Concentration of VEGF in healthy eyes
Low
With AMD, levels of VEGF
Higher
where is VEGF produced
RPE
Is the CNG channel open or closed after the biochemical cascade
Closed
When the CNG channel is closed, the is NT increased or decreased
Decreased
Excitatory cells
Ganglion and amacrine (use glutamate)
