Sleep Fragments

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Do you have an "eye" for detail?

Contributed by Klar Yaggi, MD, Yale University School of Medicine, New Haven, CT

What is abnormal about the epoch of REM sleep shown below?

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No corresponding conjugate eye movements are detected in the LOC channel.  The patient has a prosthetic left eye.

A potential difference exists across the normal eyeball with a posterior negativity centered on the retina and relative positivity at the cornea.  This approximates a dipole and makes possible recording of eye movements because eye movements change the orientation of this dipole.  By strategically placing EOG electrodes 1 cm superior and lateral to the outer canthus of one eye and another electrode 1 cm inferior and lateral to the outer canthus of the other eye, it is possible to detect conjugate horizontal and vertical eye movements by observing out-of–phase deflections (e.g. one up, one down) in the electro-oculogram tracings.

This fragment is of a patient with a prosthetic left eye which does not have a potential difference.  The arrow points out  that no eye movements are detected in the left oculogram.

Reference:

Chokroverty S, ed. Sleep Disorders Medicine: Basic Science, Technical Considerations, and Clinical Aspects. Second ed. Boston: Butterworth and Heinemann; 1999.

 

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