Instruments and Investigations

Question 1

ERG: What cell types in the retina account for each of these waves?

• a wave
• b wave
• c wave
• d wave
• Oscillations

Answer 1

• a wave: Photoreceptors
• b wave: Müller / bipolar cells
• c wave: RPE
• d wave: OFF bipolar cells
• Oscillations: Amacrine cells

Question 2

ERG: What are some congenital causes of an electronegative scotopic flash (3.0 candela/ m2) ERG?

Answer 2

1. X-linked retinoschisis
2. Congenital stationary night blindness
3. Oguchi’s disease
4. Fundus albipunctatus

Question 3

ERG: What are some acquired causes of an electronegative scotopic flash ERG?

Answer 3

1. Toxic drug retinopathies: Hydroxychloroquine, vigabatrin

2. Ocular siderosis

Question 4

ERG: What type of ERG tests macular function?

Answer 4

Pattern ERG

Question 5

ERG: What type of ERG tests rod function?

Answer 5

Scotopic low light (0.01 candela / m2) ERG

Question 6

ERG: What type of ERG tests cone function?

Answer 6

Photopic flash (3.0)
Flicker >25 Hz

Question 7

ERG: What type of ERG tests mixed rod/ cone function?

Answer 7

Scotopic flash

Question 8

ERG: What type of ERG is the only one to be affected in optic nerve damage specifically?

Answer 8

Pattern ERG as it tests ganglion cell function (N95 portion especially)

Question 9

ERG: What is the critical fusion frequency (CFF) for rods and cones respectively?

Answer 9

Rods: 25 Hz
Cones: 50 Hz

Question 10

Does the ERG measure visual acuity?

Answer 10

No. It also does not detect small localised lesions and is normal even in macular and optic nerve disease