Exam 4 -- ERG

Question 1

A standard (flash, full-field) ERG shows positive and negative deflections. Which wave, a or b, has a negative deflection? Which cell type causes it?

Answer 1

A-wave has a negative deflection and is caused by the photoreceptors.

Question 2

True or false: a macular hole would affect a standard flicker ERG.

Answer 2

False; the standard ERG tests the whole retina. You’d have to use a focal flicker ERG in order to see the effect of a specific area of the retina.

Question 3

Which type of ERG is used for inner retina and ganglion cell function, PERG or mfERG?

Answer 3

PERG

Question 4

A flicker ERG uses a 30 Hz light and looks like a sine-wave. Which type of retinopathy might cause the amplitude to decrease during the ERG?

Answer 4

Outer retina disease like diabetic retinopathy.

Question 5

True or false: ERG on a patient with Leber Congenital Amaurosis would be a flat line.

Answer 5

True.

Question 6

A full-field (standard, flash) ERG is derived primarily from the ___________ (inner/outer) retina.

Answer 6

Outer.

Question 7

What cell type is thought to cause the c-wave on an ERG?

Answer 7

RPE cells

Question 8

Which type of ERG is used for outer retina (photoreceptors and bipolar) function, PERG or mfERG?

Answer 8

mfERG

Question 9

Comparing a standard scotopic ERG to a normal photopic ERG, which is faster?

Answer 9

Photopic is faster

Question 10

If you wanted to test the entire retina function, you would use a __________ ERG. If you wanted to test a specific area, you would use a __________ ERG.

Answer 10

Entire retina: full-field. Specific area: focal.

Question 11

Comparing a standard scotopic ERG to a normal photopic ERG, which is smaller?

Answer 11

Photopic is smaller

Question 12

A standard (flash, full-field) ERG shows positive and negative deflections. Which wave, a or b, has a positive deflection? Which cell types causes it?

Answer 12

B-wave has a positive deflection and is caused by the Mueller and/or bipolar cells.

Question 13

If you were to run both a photopic flicker ERG and a scotopic flicker ERG on an RP patient, which would have the more obvious deficit?

Answer 13

Scotopic.

Question 14

Comparing a standard scotopic ERG to a normal photopic ERG, which is bigger?

Answer 14

Scotopic is bigger

Question 15

What are the three clinical applications of an ERG?

Answer 15

Assessing the patency of the retina and choroid, locating the site of damage, and separating damage to rods vs cones

Question 16

Which optic neuropathy is often tested for with PERG?

Answer 16

Glaucoma.

Question 17

Comparing a standard scotopic ERG to a normal photopic ERG, which is slower?

Answer 17

Scotopic is slower

Question 18

The early receptor potential (ERP) is a small portion of the ERG wave that is not seen clinically, since it requires a very bright light. What part of the retina causes the ERP?

Answer 18

Primarily the cones.