Eye movement recording

Question 1

What is EOG?

Answer 1

Electrooculography records eye movements by measuring the electrical potential difference between the cornea and retina using electrodes.

Question 2

Advantages of EOG:

Answer 2

Records large horizontal movements, is inexpensive, does not require head restraint, and is ideal for children.

Question 3

Disadvantages of EOG:

Answer 3

Poor resolution, frequent recalibration, noise sensitivity, and inability to measure small movements accurately.

Question 4

What is the infrared limbal reflection technique?

Answer 4

Measures IR light reflected from the limbus (sclera-iris edge) to track eye movements.

Question 5

Advantages of IR systems:

Answer 5

Sensitive, reasonable cost, can measure horizontal and vertical movements (not simultaneously).

Question 6

Disadvantages of IR systems:

Answer 6

Requires careful setup, cooperative patients, and a head restraint. Cannot record torsional movements.

Question 7

What is the scleral search coil?

Answer 7

A gold-standard device with a wire coil embedded in a contact lens to record eye movements within a magnetic field.

Question 8

Advantages of scleral search coil:

Answer 8

High sensitivity, measures all movement types (horizontal, vertical, torsional), pre-calibration, and head movement recording.

Question 9

Disadvantages of scleral search coil:

Answer 9

Invasive, uncomfortable, requires corneal anaesthesia, can cause corneal abrasions, expensive, and bulky.

Question 10

How does the Purkinje eye tracker work?

Answer 10

Measures the 1st and 3rd Purkinje reflections to calculate eye movements.

Question 11

Advantages of the Purkinje eye tracker:

Answer 11

Sensitive, accurate, non-invasive, measures horizontal and vertical movements.

Question 12

Disadvantages of the Purkinje eye tracker:

Answer 12

Expensive, limited field of view, requires a bite bar, and records one eye only.

Question 13

How do video trackers work?

Answer 13

Measure corneal reflection position relative to the pupil using infrared technology.

Question 14

Eyelink 1000+ specifications:

Answer 14

Sampling rate: up to 1000 Hz, spatial resolution: 0.01°, tracking range: 60° horizontally, 40° vertically.

Question 15

Advantages of video trackers:

Answer 15

High spatial resolution, wide tracking range, compatibility with glasses.

Question 16

Why record eye movements?

Answer 16

For differential diagnosis of nystagmus, tracking progression of diseases, and detailed analysis of eye movement characteristics.

Question 17

Eye movements recorded include:

Answer 17

Fixation, smooth pursuit, saccades, vergence, OKN, VOR.

Question 18

Clinical uses for fixation analysis:

Answer 18

Assessing nystagmus type, null zones, pre/post-surgery evaluation, unexplained symptoms.

Question 19

What is a nystagmus null zone?

Answer 19

The area where nystagmus is minimized; surgical intervention can shift this to the primary gaze position.

Question 20

Types of nystagmus waveforms:

Answer 20

Jerk (fast and slow phase) and pendular (smooth rhythmic movement).

Question 21

Common characteristics of infantile nystagmus:

Answer 21

Usually jerk nystagmus with an accelerating velocity slow phase.

Question 22

Parameters for nystagmus measurement:

Answer 22

Frequency, amplitude, and intensity.

Question 23

What are saccades?

Answer 23

Fast, accurate eye movements with predictable characteristics.

Question 24

Factors affecting saccadic latency:

Answer 24

Target predictability, complexity, distractors, forewarning period, age, attention.

Question 25

What is the saccadic main sequence?

Answer 25

Peak velocity increases with larger saccades.

Question 26

Factors reducing peak velocity:

Answer 26

Drugs, diseases (e.g., Alzheimer’s, AIDS), fatigue, age (for large amplitudes).

Question 27

How is saccadic accuracy measured?

Answer 27

By calculating gain:

Gain =
Saccadeamplitude/
Targetdistance

Question 28

What is smooth pursuit?

Answer 28

Eye tracking of moving objects to keep the image stable on the fovea.

Question 29

Stimulus for smooth pursuit:

Answer 29

Retinal image slip, movement off the fovea.

Question 30

Parameters for smooth pursuit measurement:

Answer 30

Latency, accuracy, gain

Question 31

Typical smooth pursuit gain:

Answer 31

Gain=

Eyevelocity/
Targetvelocity
​
typically 0.95 up to 30-40°/sec.

Question 32

What drives vergence movements?

Answer 32

Disparity, blur, proximity.

Question 33

Types of vergence movements:

Answer 33

Convergence, divergence, vertical vergence.

Question 34

Vergence latency:

Answer 34

Disparity-driven: Convergence ~180ms, divergence ~200ms.

Accommodative: Convergence ~300ms, divergence ~380ms.

Question 35

Case Study 1 - Bilateral INO:

Answer 35

38-year-old female with reduced adducting saccades compared to abducting saccades. Diagnosis: Bilateral Internuclear Ophthalmoplegia.

Question 36

Case Study 2 - Giant Axonal Neuropathy:

Answer 36

19-year-old male with blurred vision, gait disturbance, and horizontal diplopia. Eye recordings revealed unstable fixation and saccadic latency.

Question 37

Case Study 3 - Manifest Latent Nystagmus (MLN):

Answer 37

13-year-old with oscillopsia and R beating nystagmus. Diagnosis confirmed by eye movement recordings.

Question 38

What advancements are expected?

Answer 38

Improved accuracy, portability, and accessibility of eye movement recording systems.

Question 39

Why are recordings essential in nystagmus care?

Answer 39

For consistent care pathways, precise diagnosis, and long-term monitoring.

Question 40

How do recordings aid clinical decisions?

Answer 40

Provide objective, detailed, and reproducible data for surgical and therapeutic interventions.