Open-loop and closed-loop optokinetic nystagmus (OKN) in myasthenia gravisand nonmyasthenic subjects

Optokinetic nystagmus (ORN) eye movements of myasthenia gravis (MG) and non myasthenic ocular palsies, and normal subjects were examined under closed-l oop and open-loop conditions. The open-loop OKN condition was achieved by a dding the signal of eye-movement velocity of OKN to the computer-generated signal controlling the stimulus grating moving. The OKN was recorded by mea ns of electromagnetic search scleral coil technique. In MG patients, the op en-loop gains of OKN increased significantly after the intramuscular inject ion of an acetylcholinesterase inhibitor, neostigmine, while the closed-loo p OKN gains were not significantly changed. Both the closed-loop and open-l oop OKN gains of normal subjects and nonmyasthenic patients were not increa sed for the administration of neostigmine. The experimental results indicat ed that the open-loop OKN gain could be sensitive to reflect the changes of the function of neuromuscular junction in MG patients. (C) 2000 Academic P ress.