Electro diagnostic

Question 1

ERG

Answer 1

Recording of the eye’s electrical response to a flash of light
•Recorded through corneal electrode

•Ganzfeld stimulator (illuminates entire retina)
•Responses will only detect generalised disease

•Limitations
•No information beyond retina
•When flash ERG is normal but cortical response is abnormal unable to isolate site of lesion
•Only detects generalised defects

Question 2

Pattern ERG

Answer 2

•Checkerboard pattern (on TV)
•Sensitive to disease processes affecting the inner-retinal layers
•Abnormal response if diseases in ganglion cell layer

Question 3

Focal ERG

Answer 3

To analyse small retinal defects
•Not good for macula lesions as requires good fixation
•Either by modified ophthalmoscope or modified ganzfeld
•BUT light is scattered by optic media

Question 4

Multifocal ERG

Answer 4

•Advanced technology – available ~ 1998

Question 5

Electro-oculogram

Answer 5

Measures retinal function – dependent on the integrity of RPE layer
•Standing potential between front and back of eye
•Estimated by measuring the voltage induced as the eye looks side to side

Question 6

Eog

Answer 6

•Well lit room
•Eyes dilated
•Fix on red lights

Question 7

Arden ratio

Answer 7

Potential declines during dark adaptation & rises during light adaptation
•Arden ratio =
max amplitude under light adapted conditions
min amplitude under dark adapted conditions

Question 8

VEP

Answer 8

Measure of macula function (central 6-8°)
•But no other anatomical information

Question 9

Pattern reversal VEP

Answer 9

Measure of macula function
•Checkerboard or grating
•Estimates acuity

Question 10

Sweep VEP

Answer 10

10 second sweep
•Pattern occurs 6 times/sec then measure 6 Hz output of EEG
•Range 0.5-25 cycles/deg (6/3600 – 6/9)