Eye movement recording Flashcards
What is EOG?
Electrooculography records eye movements by measuring the electrical potential difference between the cornea and retina using electrodes.
Advantages of EOG:
Records large horizontal movements, is inexpensive, does not require head restraint, and is ideal for children.
Disadvantages of EOG:
Poor resolution, frequent recalibration, noise sensitivity, and inability to measure small movements accurately.
What is the infrared limbal reflection technique?
Measures IR light reflected from the limbus (sclera-iris edge) to track eye movements.
Advantages of IR systems:
Sensitive, reasonable cost, can measure horizontal and vertical movements (not simultaneously).
Disadvantages of IR systems:
Requires careful setup, cooperative patients, and a head restraint. Cannot record torsional movements.
What is the scleral search coil?
A gold-standard device with a wire coil embedded in a contact lens to record eye movements within a magnetic field.
Advantages of scleral search coil:
High sensitivity, measures all movement types (horizontal, vertical, torsional), pre-calibration, and head movement recording.
Disadvantages of scleral search coil:
Invasive, uncomfortable, requires corneal anaesthesia, can cause corneal abrasions, expensive, and bulky.
How does the Purkinje eye tracker work?
Measures the 1st and 3rd Purkinje reflections to calculate eye movements.
Advantages of the Purkinje eye tracker:
Sensitive, accurate, non-invasive, measures horizontal and vertical movements.
Disadvantages of the Purkinje eye tracker:
Expensive, limited field of view, requires a bite bar, and records one eye only.
How do video trackers work?
Measure corneal reflection position relative to the pupil using infrared technology.
Eyelink 1000+ specifications:
Sampling rate: up to 1000 Hz, spatial resolution: 0.01°, tracking range: 60° horizontally, 40° vertically.
Advantages of video trackers:
High spatial resolution, wide tracking range, compatibility with glasses.
Why record eye movements?
For differential diagnosis of nystagmus, tracking progression of diseases, and detailed analysis of eye movement characteristics.
Eye movements recorded include:
Fixation, smooth pursuit, saccades, vergence, OKN, VOR.
Clinical uses for fixation analysis:
Assessing nystagmus type, null zones, pre/post-surgery evaluation, unexplained symptoms.
What is a nystagmus null zone?
The area where nystagmus is minimized; surgical intervention can shift this to the primary gaze position.
Types of nystagmus waveforms:
Jerk (fast and slow phase) and pendular (smooth rhythmic movement).
Common characteristics of infantile nystagmus:
Usually jerk nystagmus with an accelerating velocity slow phase.
Parameters for nystagmus measurement:
Frequency, amplitude, and intensity.
What are saccades?
Fast, accurate eye movements with predictable characteristics.
Factors affecting saccadic latency:
Target predictability, complexity, distractors, forewarning period, age, attention.
What is the saccadic main sequence?
Peak velocity increases with larger saccades.
Factors reducing peak velocity:
Drugs, diseases (e.g., Alzheimer’s, AIDS), fatigue, age (for large amplitudes).
How is saccadic accuracy measured?
By calculating gain:
Gain =
Saccadeamplitude/
Targetdistance
What is smooth pursuit?
Eye tracking of moving objects to keep the image stable on the fovea.
Stimulus for smooth pursuit:
Retinal image slip, movement off the fovea.
Parameters for smooth pursuit measurement:
Latency, accuracy, gain
Typical smooth pursuit gain:
Gain=
Eyevelocity/
Targetvelocity
typically 0.95 up to 30-40°/sec.
What drives vergence movements?
Disparity, blur, proximity.
Types of vergence movements:
Convergence, divergence, vertical vergence.
Vergence latency:
Disparity-driven: Convergence ~180ms, divergence ~200ms.
Accommodative: Convergence ~300ms, divergence ~380ms.
Case Study 1 - Bilateral INO:
38-year-old female with reduced adducting saccades compared to abducting saccades. Diagnosis: Bilateral Internuclear Ophthalmoplegia.
Case Study 2 - Giant Axonal Neuropathy:
19-year-old male with blurred vision, gait disturbance, and horizontal diplopia. Eye recordings revealed unstable fixation and saccadic latency.
Case Study 3 - Manifest Latent Nystagmus (MLN):
13-year-old with oscillopsia and R beating nystagmus. Diagnosis confirmed by eye movement recordings.
What advancements are expected?
Improved accuracy, portability, and accessibility of eye movement recording systems.
Why are recordings essential in nystagmus care?
For consistent care pathways, precise diagnosis, and long-term monitoring.
How do recordings aid clinical decisions?
Provide objective, detailed, and reproducible data for surgical and therapeutic interventions.
