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?
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.
