Recording device

Ag/AgCl electrodes

Video camera

Copper coil embedded in silicon ring

Principle

Corneo-retinal dipole potential

Image processing

Voltage changes induced in coil of wire moving in oscillating magnetic field

Recording of horizontal eye movement

Good

Very good

Excellent

Recording of vertical eye movement

Unacceptable

Very good

Excellent

Recording of torsional eye movement

Not possible

2D—not possible3D—Good

Excellent

Approximate accuracy

1-2°

1°

0.02°

Head movement artefact

High

Low

Nil

Sampling rate

>150Hz

Most clinical systems: 50 Hz Research systems: 200 Hz

1000 Hz

Amplifier drift

Yes

No

No

Calibration

Repeatedly

Once

Once

Errors due to: Blinks Changes inroom lighting Myogenic activity

Yes

Yes

Yes

Yes

No

No

No

No

No

Patient tolerance

> 1 hour

30–45 minutes

>30 minutes

Value

Simple, inexpensive, readily available, clinical tool

More expensive, 2D recording relatively simple, good clinical tool except for saccades

Excellent research technique, too invasive for routine clinical use