Types of Ocular Artifacts

Ocular artifacts in EEG recordings can manifest in various forms, each associated with specific eye movements or activities.

Blink Artifact:

o Description: Produced by rapid eye movements associated with blinking.

o Characteristics: Appears as a bifrontal, diphasic, synchronous slow wave limited to the frontal region. The waveform is related to the rate and duration of eye movement.

o Identification: The artifact decreases in amplitude with distance from the orbits and does not extend into the central region.

2. Eye Flutter Artifact:

o Description: Result of rapid eyelid flutter.

o Characteristics: Typically seen in the alpha frequency range and limited to the anterior frontal region. May not always be time-locked to stimulation.

o Differentiation: Waveform differences help distinguish it from 3 Hz epileptiform activity.

3. Lateral Gaze Artifact:

o Description: Occurs during lateral eye movements.

o Characteristics: Includes positive and negative phase reversals at specific electrodes corresponding to the direction of gaze. Has a field that is maximum across the temples and frontal poles.

o Identification: Most apparent during drowsiness and produces rhythmic, slow artifact with a frequency less than 1 Hz.

4. Rapid Eye Movements (REMs) of REM Sleep:

o Description: Associated with lateral gaze movements during REM sleep.

o Characteristics: Waveform differs from lateral gaze during wakefulness, showing asymmetrically quicker rise than fall. Location is similar to other artifacts from lateral gaze.

o Differentiation: Specific movement features distinguish REM artifact from other ocular artifacts.

5. Electroretinogram Artifact:

o Description: Produced by photic stimulation and time-locked to the strobe.

o Characteristics: Monomorphic waveform limited to specific frontal electrodes. Distinguished from photomyogenic artifact by waveform and field characteristics.

o Identification: Covering an eye during stimulation can help diminish the artifact from the ipsilateral frontal polar electrode.

These types of ocular artifacts demonstrate the diverse ways in which eye movements and activities can influence EEG recordings. Understanding their characteristics and distinguishing features is crucial for accurate interpretation and differentiation from other EEG patterns.

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