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VEPs 1
Visual evoked potentials 1
Question | Answer |
---|---|
Two types of VEP | flash, pattern reversal |
Type of VEP used to evaluate retinal dysfunction | Flash |
Lesions in this region cause loss or slowing of the evoked potential generated by stimulating the affected eye | optic nerve |
Lesions at or near this region are not purely monocular and may affect incongruous portions of the visual fields of both eyes, creating confusing VEPs that are challenging to localize | optic chiasm |
Lesions of this region produce abnormalities of the VEP elicited from one visual hemifield | optic tract |
Lesions of this region of the brain produce abnormalities in the VEP, but these changes are complex; the VEP typically is not used to diagnose abnormalities in this region | occipital cortex |
When performing VEPs, separate normal controls are needed for subjects up to age __ and over age __ | 5, 60 |
Visual acuity for VEPs should be better than 20/__ for squares of 1 degree or less | 200 |
Visual acuity of 20/200 should allow patients to see VEP patterns of __ degree or less | 1 |
The rate of pattern reversal for VEPs is __ - __ per second | 1, 2 |
Check size should be __ - ___ ' for full field stimulation from the central retina and __ - __ ' for hemifield stimulation of the peripheral retina | 28, 31, 50, 90 |
The field side should be over __ degrees for full field stimulation and __ - __ degrees for hemifield stimulation | 8, 10, 16 |
The three channels used for a standard full field stimulation (without ERG) | RO-MF, MO-MF, LO-MF |
Midline occipital electrode is __ cm above the inion | 5 |
In VEPs, __ refers to the midline occipital electrode | MO |
In VEPs, __ refers to the left occipital electrode | LO |
In VEPs, __ refers to the left occipital electrode | RO |
In VEPs, __ refers to the left temporal electrode | LT |
In VEPs, __ refers to the right temporal electrode | RT |
In VEPs, LO is __ cm lateral to MO | 5 |
In VEPs, RO is __ cm lateral to MO | 5 |
In VEPs, LT is __ cm lateral to MO | 10 |
In VEPs, RT is __ cm lateral to MO | 10 |
In VEPs, midline frontal is represented by __ | MF |
In VEPs, MF is __ cm behind the inion | 12 |
The ground electrode for VEPs is usually placed at the __ of the head | vertex |
Channel one for standard VEPs with full field stimulation | RO-MF |
Channel two for standard VEPs with full field stimulation | MO-MF |
Channel three for standard VEPs with full field stimulation | LO-MF |
If channel four is used with VEPs with full field stimulation, it usually represents __ with __ and __ electrodes | ERG, infraorbital, lateral orbital |
For right hemifield VEPs, typical channel one | RO-MF |
For right hemifield VEPs, typical channel two | MO-MF |
For right hemifield VEPs, typical channel three | LO-MF |
For right hemifield VEPs, typical channel four | LT-MF |
For left hemifield VEPs, typical channel one | RT-MF |
For left hemifield VEPs, typical channel two | RO-MF |
For left hemifield VEPs, typical channel three | MO-MF |
For left hemifield VEPs, typical channel four | LO-MF |
Typical low frequency filter for VEP is from __ - __Hz | 0.2, 1 |
Typical high frequency filter for VEP is from __ - __ Hz | 200, 300 |
The typical number of responses averaged for a full field VEP is between __ and __ | 100, 200 |
The typical number of responses averaged for a hemifield VEP is __ | 200 |
The sweep length for most VEPs is __ msec, but can be up to __ msec for infants and greatly delayed VEPs | 250, 500 |
The typical full field normal VEP peaks | N75, P100, N145 |
The typical ipsilateral hemifield VEP peaks | N75, P100, N145 |
The typical contralateral hemifield VEP peaks | N75, P105, P135 |
The three criteria for abnormal full field VEPs | absence of peaks, abnormal long latency p100, abnormal long p100 interocular latency |
The criteria for abnormal hemifield VEPs | Absence of any peaks ipsilateral and contralateral to the stimulated hemifield |
Higher checkerboard reversal rates > 4 / second lead to this change in the test | Increased latency |
Slower checkerboard reversal rates < 2 / second led to this change in the test | Slower testing |
The two important components to checks: __ between checks and __ of check borders | contrast, sharpness |
At low contrast levels between checks, there is a __ (increase/decrease) of the VEP latency and a __(increase/decrease) in amplitude | increase, decrease |
Contrast is a function of __ | luminance |
Contrast = ____ / ___ | Lmax - Lmin / Lmax + Lmin |
Bandwidth for VEPs is usually __ - __ Hz | 1, 100 |
Visual field size is < than __ degrees with a check size of __ minutes | 10, 30 |
The P100 is an __ (upgoing / downgoing) wave | upgoing |
The __ wave of the VEP is thought to be generated by projections of the optic radiations to the visual cortex with contribution of the visual cortex itself | P100 |
This wave __ of the VEP may be due to the lateral geniculate activity | N75 |
This wave __ of the VEP may be due to activity of visual association cortex | N145 |
THe normal latency of the P100 is between __ and __ seconds | 90, 110 |
The P100 is also known as __ | P1 |
The N145 is also known as __ | N2 |
The type of VEP used in young children | flash VEP |
The VEP reaches adult values by the end of age __ for large checks (50-60') and by age __ for small checks (12-15') | 1, 5 |
Amplitude of VEPs increases until age ~ __ | 40 |
P100 latency remains stable during adulthood but increases after age __ | 60 |
__ (women/men) have shorter P100s | women |
With loss of visual acuity below 20/200, the VEP latency is __ (increased/decreased) and the amplitude is __ (increased/decreased) | increased, decreased |
The maximal latency of the P100 with pattern reversal stimulation in msec | 117 |
The maximal latency of the P100 with flash stimulation in msec | 132 |
The maximal interocular latency difference the P100 with pattern reversal stimulation in msec | 6 |
The maximal interocular latency difference of the P100 with flash stimulationstimulation in msec | 6 |
The maximal interocular amplitude difference of the P100 with pattern reversal stimulation in microvolts | 5.5 |