New Nystagmography System Detects Causes of Dizziness

A new video nystagmography system (VNG) offers a precise and extensive suite of ocular motor tests for neurologic, otologic, and vestibular disorder evaluation.

The I-Portal-VNG offers an extensive battery of tests using the proprietary I-Portal 100 Hz Eye Tracker goggle, including torsional, horizontal, vertical, and pupilometry eye measurements with the aid of a laser diode system than can generate a wide range of stimuli; integrated fixation; and real time video, data, and analysis using a push button interface designed for easy use by all clinicians. The system is capable of capturing saccades accurately at 100 frames per second, and new analysis software evaluates not only the main (first) corrective saccade but also additional secondary (micro corrective) saccades. A full field light-pattern stimulus provides true optokinetic (OPK) system tests with precise digital control. Additionally, an integrated fixation light makes caloric fixation simple and accurate, and an interactive pedal control gives users the ability to easily conduct all tests. The I-Portal-VNG is a product of Neuro Kinetics (NKI, Pittsburgh, PA, USA)

"With improvements to our saccade test, clinicians can now include up to 100 random or fixed saccades to increase statistical power of their results quickly,” said Terri Ives, M.D., an audiologist and NKI's director of clinical audiology.

Eye saccades are quick, simultaneous movements of both eyes in the same direction. Initiated by the frontal lobe of the brain, saccades serve as a mechanism for vision fixation, rapid eye movement (REM), and the fast phase of optokinetic nystagmus. In addition, the human eye is in a constant state of vibration, oscillating back and forth at a rate of about 30-70 Hz. These tiny movements are termed microsaccades and are roughly 20 arcseconds in excursion, imperceptible under normal circumstances. They serve to refresh the image being cast onto the rod cells and cone cells at the back of the eye.

Nystagmus is characterized by the combination of "slow phases,” which usually take the eye off the point of regard, interspersed with saccade-like "quick phases” that serve to bring the eye back on target. Pathological slow phases may either be due to an imbalance in the vestibular system, or damage to the brainstem "neural integrator” that normally holds the eyes in place.

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