Ocular Artifacts

Ocular artifacts in EEG recordings are commonly caused by movements of the eyes, such as blinking, eye flutter, and eye movements associated with eye opening and closure. These artifacts can mimic epileptiform discharges and other EEG patterns, making them important to recognize and differentiate.

Nature of Ocular Artifacts:

o Ocular artifacts are primarily due to the movement of the electrical dipoles created by the eyes, particularly during activities like eye opening, closure, and directed gaze.

o The movement of these dipoles generates changing electrical fields that appear as EEG activity, with characteristics such as slow waves and spikes.

o Ocular artifacts are typically limited to the frontal region and do not extend into the central region of the brain.

2. Differentiation from Epileptiform Discharges:

o Ocular artifacts can sometimes appear as bifrontal spike and slow wave complexes, resembling interictal epileptiform discharges.

o However, the field distribution and spike waveform of ocular artifacts differ from those of epileptiform discharges, helping in their differentiation.

3. Characteristics of Specific Ocular Artifacts:

o Eye Flutter Artifact: Rapid eyelid flutter producing flutter artifact in the alpha frequency range, limited to the anterior frontal region.

o Slow Roving Eye Movement Artifact: Characterized by shallow slopes and low voltage slow activity, with electrode phase reversal locations similar to lateral eye movement artifacts.

o Lateral Eye Movement Artifact: Distinguished by a horizontal, frontal dipole and abrupt transitions between positive and negative slopes.

4. Identification and Differentiation:

o Using supraorbital and infraorbital electrodes can help definitively differentiate ocular artifacts from other patterns.

o The presence or absence of eye movements, along with waveform differences, can aid in distinguishing ocular artifacts from other EEG patterns.

These points highlight the importance of understanding ocular artifacts in EEG interpretation and the methods available to differentiate them from epileptiform discharges and other patterns.

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