Final: Electro-Oculography Flashcards
What is biopotential?
An electric potential (voltage) that is mea-sured between points in living cells, tissues, and organisms, and which accompanies all biochemical processes.
Describes the transfer of information between and within cells
What happens to create the resting potential?
At rest, Na+/K+ pumps in a neuron’s membrane keep a higher concentration of Na+ outside the cell and a higher concentration of K+ inside.
What happens when neuron is stimulated?
Na+ ions rush into the cell, causing a change in the voltage across the membrane.
[Na+] is greater in the ________ fluid.
extracellular
[K+] is greater in the ________ fluid.
intracellular
What pushes Na+ into and K+ out of the cell.
Concentration gradient
What causes electrical current?
Movement of ions across the membrane
The ‘_________’ is characterized by the membrane potential being constant over time.
resting state
What is equilibrium potential?
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 ______: negative in and positive out.
polarized
What does electrooculogram (EOG) measure?
Measures the resting potential of the retina.
Unlike ERG, it is NOT recorded in response to a direct visual stimulus.
How is the eye like a battery?
More positive towards the from and more negative towards the back.
The NORMAL “standing potential” of the eye requires a healthy _______________.
retinal pigmented epithelium
What can change the standing potential of the eye?
retinal illumination, eye movements of constant amplitude
What is a EOG a key test for?
Determining whether or not the RPE is healthy or not.
Which membrane in the retina has the greatest potential?
RPE
What affects did drugs that affect standing potential have on the eye?
It damaged the RPE
How is the EOG operated?
1) Dilate the eyes and light adapt patient in a well-lit room.
2) Attach electrodes to medial and lateral canthi and ground electrode on forehead or earlobe.
3) Place patient in a Ganzfeld bowl or in front of a screen on which you can place two fixation lights 20 to 40 degrees apart. (Chin rest may be used to steady the head.)
4) Explain procedure to patient and have patient practice several times during the first 5 minutes to record ‘baseline’ data.
5) Patient’s task: Patient keeps his or her head still while alternating the eyes back and forth to fixate on the
two lights. (i.e., patient makes saccades between
the two fixation lights).
6) After the 5 minute training period, the lights are turned off. About every 1 minute, the patient is asked to move his/her eyes back and forth between the two fixation lights for about 10-15 seconds and the voltage changes are recorded.
7) After 15 minutes, the room lights are turned on (and the Ganzfeld illuminated, if used). The eye movement recordings are repeated for 10-15 seconds every 1 minute for the next 15 minutes.
8) The data is graphed to show the changes in voltage through 15 minutes of dark adaptation and 15 minutes of bright light.
When pt makes saccade during EOG, about how much is voltage is produced for each saccade?
5 millivolts
Typically, the voltage becomes ______ in the dark, reaching its lowest value after 8-12 minutes. This is called the ________.
Smaller; DARK TROUGH
When the lights are turned on, the potential _____ this is called the _________ and it peaks in about 10 minutes.
rises; LIGHT RISE
What does the EOG record?
The EOG records a SLOW potential change that occurs with prolonged changes in retinal illuminance.
What does DC amplification give a better record of?
Gives a better record of actual eye position. Easily detect overshoots.
What is a pro of using AC amplification?
It does not take into account of electro drift so it wouldn’t change the baseline signal.
Is AC or DC amplification used more often?
AC amplification
What is a problem with AC recordings? What value do we use for AC recordings?
Falloff occurs in the AC recordings as a consequence of the manner in which the AC amplification works. Use the value just before falloff begins.
What does the Arden Ration measure? What are the values? What do abnormal results indicate?
Measures whether the RPE is normal or not.
Normal: > 1.65 – 1.80
Abnormal: < 1.65 – 1.80
Abnormal result indicates “unhealthy” pigment epithelium!
EOG is particularly useful in __________________.
Vitelliform macular degeneration (Best’s Disease)
Describe Best’s Macular Dystrophy characteristics and progression.
- Autosomal dominant macular dystrophy with variable penetrance.
- In both males and females equally.
- Presents in childhood (1st or 2nd decade) with yellow macular yolk-like lesion
- Several stages over many years, with increasing potential for adverse visual outcome.
- Hallmark is markedly abnormal electro-oculogram (EOG) in ALL stages of progression AND in phenotypically normal carriers.
What are the Stages of Best’s Disease?
Stage 0 – normal fundus, abnormal EOG
Stage I – RPE disturbance in macula
Stage II:
- “Egg yolk” lesion
- First few years of life (3-15 yr)
- Lipofuscin accumulation beneath or within RPE
- Usually single lesion
- Visual acuity 20/20-20/40
- Early blockage on FA with late hyperfluorescence
Stage IIa:
- “Scrambled egg” or vitelliruptive stage
- Breakup of vitelliform cyst with changing appearance of yolk.
Stage III
- “Pseudohypopyon”
- Second decade
- Lesion ruptures into the subretinal space & gravitates inferiorly
- Decrease in visual acuity
- May be associated with hemorrhage
- Early hyperfluorescence, late staining of superior lesion
Stage IVa:
-Atrophy of RPE produces orange-red lesion in macula
Stage IVb:
-White hypertrophic scar of fibrous tissue in macula
Stage IVc:
-Neovascularization of the fibrous scar
What is hypopion?
Accumulation of white blood cells in the anterior chamber as a result of significant inflammation and/or infection
Electrophysiology of Best’s Disease.
-Full field ERG is normal
- EOG – severe loss of light response
- Characteristically abnormal
- Arden ratio (light-dark ratio) < 1.5
- Marker for gene carriers w/ normal DFE - Distinguishes from adult vitelliform disorders
- Peripheral VF-normal
- Dark adaptation - normal
Pathophysiology of Best’s Disease.
- Disorder of retinal pigment epithelium (RPE)
- Lipofuscin accumulates within RPE cells and in sub- RPE space.
- RPE degenerates in some cases
- Secondary loss of photoreceptor cells may occur, but full-field ERG typically normal
What is lipofuscin?
any of several brown pigments similar to melanin that accumulate in animal cellswith age and are products of oxidation of lipids and lipoproteins.
Genetics of Best’s Disease
- Mutation in VMD2 gene
- Long arm chromosome 11 (Ch 11q13)
- Encodes bestrophin-1 – RPE-specific protein
What kind of testing is becoming the standard diagnostic test over EOG for Best’s Disease?
VMD2 gene testing
Prognosis of Best’s Disease
- Most retain vision for reading or driving
- Severe vision loss is rare, > 40 years
- Acute visual loss may occur with development of choroidal neovascular membrane (CNV)
In the Mohler and Fine study, Most eyes with stage 1 did NOT progress to stage 2 over ____ years
8-10
In the Mohler and Fine study, what happened if the stage 2 developed?
all eyes progressed further
In the Mohler and Fine study, what percent had VA’s of 20/40 or above?
77%
In the Mohler and Fine study, what percent of patients had atrophic or fibrous scars lost 2+ lines over 8-10 years
19%
Patient care of Best’s Disease
Screen family members:
- Many are asymptomatic
- Approximately 5% of carriers have a normal fundus.
- DFE (dilated funds exam)
- EOG or VMD2 testing
- Genetic counseling
