Toward an implantable functional electrical stimulation device to correct strabismus.
OBJECTIVE
To investigate the feasibility of electrically stimulating the lateral rectus muscle to recover its physiologic abduction ability in cases of complete sixth cranial (abducens) nerve palsy.


METHODS
In the feline lateral rectus muscle model, the effects of a charge-balanced, biphasic, current-controlled stimulus on the movement of the eye were investigated while stimulation frequency, amplitude, and pulse duration was varied. Eye deflection was measured with a force transducer. Denervated conditions were simulated by injection of botulinum toxin A.


RESULTS
Three chemically denervated and 4 control lateral rectus muscles were analyzed. In control lateral rectus muscles, the minimum fusion frequency was approximately 170 Hz, and the maximum evoked abduction was 27 degrees. The minimum fusion frequency was unchanged after 4 weeks of chemical denervation. Stimulation of chemically denervated lateral rectus muscle resulted in 17 degrees of abduction. For both innervated and chemically denervated lateral rectus muscle, frequencies greater than 175 Hz yielded very little increase in abduction. Modulating amplitude produced noticeable movement throughout the tested range (0.2 to 9 mA).


CONCLUSIONS
Results from the feline lateral rectus muscle showed that electrical stimulation is a feasible approach to evoke a contraction from a denervated lateral rectus muscle. The degree of denervation of the feline lateral rectus muscle was indeterminate. Varying the stimulation amplitude allowed greater eye movement. It is very likely that both frequency and amplitude must be modulated for finer control of static eye position.
Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, California 90095, USA. velez@jsei.ucla.edu
Federico G
FG
Velez
Jun
J
Isobe
David
D
Zealear
Jack W
JW
Judy
V Reggie
VR
Edgerton
Stephanie
S
Patnode
Hyowon
H
Lee
Brian T
BT
Hahn
D020434:Abducens Nerve Diseases / Q000628:therapy*; D000818:Animals; D019274:Botulinum Toxins, Type A / Q000494:pharmacology; D002415:Cats; D003714:Denervation; D004195:Disease Models, Animal; D004599:Electric Stimulation Therapy / Q000295:instrumentation* / Q000379:methods*; D004566:Electrodes; D005240:Feasibility Studies; D009498:Neurotoxins / Q000494:pharmacology; D009801:Oculomotor Muscles / Q000502:physiology*; D013285:Strabismus / Q000628:therapy*; D014159:Transducers
D009498:Neurotoxins; D019274:Botulinum Toxins, Type A