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An electric potential (voltage) that is measured between points in living cells, tissues, and organisms, and which accompanies all biochemical processes
At rest, Na/K pumps in a neuron's membrane keep a higher concentration of ___ outside the cell and a ___ inside the cell, creating a voltage difference called ____.
When stimulated, Na flows down its concentration gradient and flows ___ the cell, while K flows ___ the cell.
The voltage required to exactly oppose the flow of any given ion is the equilibrium potential for that ion
At rest, the membrane is slightly polarized: ____ inside and _____ outside.
Measures the resting potential of the retina
Eye movements are used as an indirect way of measuring the resting potential
Eye movements of constant amplitude can be used to detect changes in the:
Retinal illumination (can/cannot) change the standing potential
scotopic and photopic conditions will give different results!
Since the eye is polarized, changes in the eye's polarization when the eye changes horizontal orientation in the socket can be detected by skin electrodes placed where?
The resting potential of the retina makes the eye act like a polarized battery! It is more positive towards the ____ and more negative towards the _____.
Eye movements of constant amplitude can be used to detect changes in the _______ _____.
____ ______ can change the standing potential
Can you have different results of standing potential be different if you measure it under scotopic and photopic conditions.
Resting potential is more + towards the _____ and more (-) towards the ____.
The normal standing potential of the eye requires a healthy...
What is a direct way to measure the health of the RPE?
measure the standing potential
What layer of the retina has the greatest electrical potential?
The cornea is + or - ?
The retina is + or - ?
When light hits the photoreceptors there is a increase of decrease in extracellular K+ concentration around the photoreceptors?
When light hits the photo receptors A change in the concentration of an unknown substance called?
After light hits photoreceptors and causes a change in concentration, there is an increase in the flow of ___ out of the basal membr of RPE, which causes _____________.
- light peak polarization
Does EOG measure the response to a stimulus?
NO (stimuli is used so the pt has something to fixate on)
Describe what happens during an EOG procedure
There are 2 stimuli that the pt is told to move their eyes back and forth to look at.
A pt must have equal ______ for the measurement to be most accurate?
Where do you attach the electrodes to for an EOG?
medial and lateral canthi and ground electrode on forehead or earlobe
Name of bowl used in EOG and how far are fixation lights set apart?
Fixation lights in an EOG are used to ensure the saccades have...
Movement of eyes during EOG produces a voltage swing of ~ __ microvolts that is recorded
What is the lighting during an EOG?
- lights are turned off after 5 min training period; after 15 minutes lights are turned on
- (15 minutes of dark adaptatin and 15 minutes of bright light recorded)
Explain the dar trough
voltage becomes smaller in the dark, reaching its lowest value after 8-12 minutes
less illumination of retina = decrease in resting potential of eye
When lights are turned on, the potential rises and peaks at about 10 minutes; this is called the ?
IN an EOG amplitude is recorded in
Smallest voltage change in an EOG occurs...
during dark (dark trough)
EOG result graph: black data points represent...
the magnitude of the voltage swing with the eye mvnt
EOG x axis and yaxis represent?
- x axis: time in minutes
- y axis: amplitude of saccades in milivolts
EOG signals are very small so they have to be _____
Amplified (DC or AC)
This amplifier will more faithfully reproduce the square wave voltage changes that take place when the pt looks back and forth and gives a better record of actual eye position
Which amplication is used more frequently?
Which amplification works better when you are studying eye movements? which one when you are studying RPE health?
What is the arden ratio?
(light peak)/(dark trough)
What are the normal ranges for an arden ratio? abnormal?
- Normal: >1.65 -1.80
- Abnormal: <1.65-1.80
Abnormal EOG result indicates..
EOG is helpful in diagnosis what disesase?
Vitelliform macular degeneration (BEst's disease)
Best's macular dystrophy is..
affects males or females more?
]those with mild formes of the disease are called?
- autosomal dominance
- male = female
Best's macular dystrophy presents when with what?
childhood 1-2nd decade with a yellow macular yolk-like lesion
Stages of Bests
Stage 0: normal fundus, abnormal EOG
Stage 1: macular RPE disturbances-foveal pigment mottling and hypopigmentation, (-)FLR
- Stage 2- "egg yolk" lesion,
- Stage 2a: scrambled or fried egg appearance (vitelliruptive stage)
Stage 3-pseudohypopion stage
- Stage 4a- atrophy of RPE produces orange red lesion in macula; resorption of vitelliform lesion
- Stage 4b: white hypertropic scar of fibrous tissue in macula; -fibrotic, gliotic-appearing scar-atrophic changes in RPE & choriocapillaris
Stage 4c: neovasc of fibrous scar
What is the hallmark of Best's macular dystrophy?
markedly abnormal EOG in all stages of progression and in phenotypically normal carriers
What is difference on EOG with Best's pt vs normal?
light rise will not be present
(line at bottom of graph shows when light is turned on and off)
When does Stage 2 (egg yolk) occur?
what happens in RPE
visual acuity is around?
- first few years of life (3-15years)
- lipofuscin accumulates beneath or w/in RPE
When does stage 3 occur (pseudohypopion)?
What happens to visual accuity?
What happens during an FA?
- second decade
- early hyperfluorescence, late staining of superior lesion
If you saw a first time elderly pt, how could you tell if they had Best's or macular degeneration??
armd will have normal EOG, OCT could look the same
What does and ERG look like in Best's
full field ERG is normal
What is charactistically abnormal on EOG for Best's?
severe loss of light response
What is a typical Arden ratio in Bests?
Why is dark trough in a Best's pt normal? why is a VF normal?
- Dark adaptation is normal since rod's are not affected.
- Damage is in fovea not in periphery
What are products of oxidation of lipids and lipoprotiens that are brown pigments similar to melanin that accumulate in animal cell with age?
Best's is a mutation of what gene?
VMD2, long arm chromosome 11 (Ch11q13), encodes bestrophin-1: RPE specific protien
Visual prognosis for Best's? What is vision threatening event that can occur?
- Usually have decent vision for reading or driving.
- CNV (choroidal neov)
What should you do if you have a pt with Best's/carrier?
- screen family, DFE, EOG and VMD2 testing
- **Genetic counceling and monitoring
Apporx how many carriers have normal fundus?
What is the treatment for Best's?
- No effective treatment to stop progression of vitelliform lessions.
- photodynamic therapy if they develop a CNVM
- Intravitreal bevacizumab (Avastin) to dry up leakage of neov/vessels