Ch. 16: Gross Electrical Potentials

Question 1

is it true that the font of the eye has a positive charge relative to the back?

Answer 1

yes

Question 2

under what conditions is the EOG substantially larger?

Answer 2

under light-adapted conditions

Question 3

what makes up the Arden Ration?

Answer 3

ratio of the light rise to the dark trough

Question 4

what is considered an abnormal Arden ratio?

Answer 4

less than 165%-180%

Question 5

how long until the EOG reaches the minimum (dark trough)?

Answer 5

8 mins

Question 6

how long until the EOG reaches the maximum (light rise)?

Answer 6

10-15 mins

Question 7

how does Best’s Disease affect the EOG readings?

Answer 7

characterized by a reduced light rise

Question 8

what is the full-field ERG mainly derived from?

Answer 8

the outer retina

Question 9

is the a-wave in the ERG positive?

Answer 9

no. negative

Question 10

is the b-wave in the ERG considered the afterpotential?

Answer 10

no. the c-wave is the afterpotential (b-wave is positive)

Question 11

which wave is associated with the photoreceptors?

Answer 11

a-wave

Question 12

which wave is associated with the muller/bipolar cells?

Answer 12

b-wave

Question 13

which wave is associated with the RPE?

Answer 13

c-wave

Question 14

what is needed for a scotopic-dominated ERG?

Answer 14

obtained by stimulating a dark-adapted retina with a dim short wavelength

Question 15

what is needed for a photopic-dominated ERG?

Answer 15

light-adapted patient is exposed to a relatively bright middle-wavelength stimulus

Question 16

which ERG (scotopic or photopic) is larger and slower?

Answer 16

the scotopic

Question 17

what type of ERG would help to evaluate certain lesions on the retina?

Answer 17

Focal ERG

Question 18

is it true that PERG’s affect the inner retina?

Answer 18

yes (in particular the retinal ganglion cells)

Question 19

what type of ERG is used to examine the outer retina (in particular the rods and cones)?

Answer 19

full field ERGs (flash or flicker)

Question 20

why would a PERG be able to detect abnormalities in early glaucoma?

Answer 20

because glaucoma is a disease that affects ganglion cell function

Question 21

what do individual wavelets in transient VEP’s represent?

Answer 21

activity of different regions of the brain, primarily cortical areas

Question 22

what elicits a larger amplitude VEP?

Answer 22

a high-contrast patterned stimulus

Question 23

T/F? the amplitude of a visually evoked potential, for a given spatial frequency is proportional to the stimulus?

Answer 23

true

Question 24

what type of VEP does a foveal stimulus produce?

Answer 24

strong

Question 25

do parafovel stimulus elicit a weak response?

Answer 25

yes

Question 26

in PERG what happens when the you reduce the stimulus size by half?

Answer 26

it reduces the amplitude by half

Question 27

what does a reduced VEP and normal PERG indicate?

Answer 27

postretinal problem

Question 28

what does a reduced VEP and PERG indicate?

Answer 28

retinal lesion