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Fundus
Only area of teh eye where vessels are directly visible
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Electroretinalgram
Objective measure of retinal transduction
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Blood-retina barrier
Prevents certain drugs and other substance from entering the eye, this is made by Pigment Epithelium derived factor
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Retinal hemorrhage
- Blood vessels leak or rupture in the eye
- Common in diabetes, high BP, blood disorders, trauma, or aging
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Retinal vein occlusion
- Painless loss of vision
- Often related to hypertension, elevated lipids, and diabetes
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Diabetic retinopathy has what two types
- Nonproliferative - Small vessel damage causing blurred vision
- Proliferative - Retinal ischemia stimulates the formation of new vessels causing hemorrhaging and scaring, edema, detachment and loss of vision
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Retinopathy of prematurity
- Abnormal new blood vessel growth, leading cause of childhood blindness in western countries
- Treated with anit-VEGF and photocoagulation
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What is the danger of detached retina
If not fixed quickly it can cause blindness, it isn't painful so it can be neglected
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Transmission of neuronal impulses goes through what cells in the retina
- Photoreceptors
- Bipolar neurons
- Ganglion cells
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What is the outer segment of a photoreceptor
- Site of phototransduction
- Made of Optic disks
- Photo pigment molecules embedded in the disks
- Constantly renewed
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What is the inner segment of a photoreceptor cell
- Supplies energy necessary for the restoration of visual pigments
- They contain the nucleus and organelles
- They are connected to the outer segment by a stalk
- These are not renewed
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Rhodopsin
Photosensitive protein complexes in the outer segment of the photoreceptors
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What are the parts of Rhodopsin
- Opsin
- - G protein coupled receptor w/ 7 transmem. parts
- - Transmembrane parts sense the diff. wavelangths
- Retinal
- - Vit A derivative
- - Undergoes conformational changes in light
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Photoreceptors don't make an action potential but do make a
Reaction potential that can be graded
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What process happens in photoreceptors when exposed to light
- They undergo a conformational change from 11 cis-retinal to all trans retinal photopigment
- Activation of transducin
- Activation of phosphodiesterase
- Decreased cGMP
- Closure of Na+ channels
- Hyperpolarization
- Decreased release of synaptic transmitter
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What happens to a photoreceptor in the dark
- 11-cis retinal is bound to opsin
- cGMP levels are high
- Na+ channels open
- Depolarization
- Increase release of transmitter (Glut)
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The Fovea only contains
Cones there is a 1:1 ratio with ganglion cells here
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Where are the rods found in abundance
Peripheral retina
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What is the difference in sensitivity to light between the rods and cones
- The Rods have a very high sensitivity Cones have a low sensitivity
- Rods are used most at night
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When a dark adapted person moves to light, decomposition is
Faster then the adaption to dark from light
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Rod vision is specialized for
- Dim light
- Motion
- Peripheral vision
- Not good at detail
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Why don't rods provide a sharp image
- Adjacent rods are connected by gap junctions and share their changes in membrane potential
- Several nearby rods often share a single circuit to one ganglion
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What happens in Vitamin A deficiency
- Night Blindness
- Synthesis of retinal is impaired
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What happens in Hypervitaminosis A
Signs of poisoning with nausea, vomiting, headache, dizziness, blurred vision, and loss of muscular coordination
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Retinitis pigmentosa
- Progressive dysfunction of mostly Rods
- Photoreceptor atrophy
- Tunnel vision
- Night blindness
- Progressive loss of peripheral vision
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What is the comparison in prevalence of the different cones
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What are we not born with that gives us the most acute vision
Fovea
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What are the symptoms of Macular degeneration
- High acuity vision loss
- Dark spots and cloudiness in central area of vision
- Yellow depositions (Drusen)
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Achromatopsia
Color blindness (X chromosome)
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What is the most common type of color blindness
Red-green (most common in men)
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What is the role of the pigment epithelial cells
- Light absorption
- Blood retina barrier
- Phagocytosis
- Secretion (growth factors)
- Vit A storage
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Accumulation of lipofuscin (cellular debris) in the retinal pigment epithelium may
Make retina more sensitive to damage from chronic light exposure
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Albinismus causes what symptoms in the eyes
- Inability to synthesize melanin
- Light blue eyes (rarely red)
- Lack of pigment
- Vision lacks fine details
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What makes optical allusions possible
The eyes detect the contrast of light more then the intensity
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Retinal ganglion cell axons are not
Myelinated
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Papilledema
Optic disk swelling that is caused by increased intracranial pressure
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