Final: Electro-Oculography Flashcards
(42 cards)
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.
