The effect of acute superior oblique palsy on torsional optokinetic nystagmus in monkeys.
OBJECTIVE
To investigate the effects of acquired superior oblique palsy (SOP) and corrective strabismus surgery on torsional optokinetic nystagmus (tOKN) in monkeys.


METHODS
The trochlear nerve was severed intracranially in two rhesus monkeys (M1 and M2). For each monkey, more than 4 months after the SOP, the ipsilateral inferior oblique muscle was denervated and extirpated. For M2, 4 months later, the contralateral inferior rectus muscle was recessed by 2 mm. tOKN was elicited during monocular viewing of a rotating stimulus that was rear projected onto a screen 43.5 cm in front of the animal. Angular rotation of the stimulus about the center was 40 deg/s clockwise or counterclockwise.


RESULTS
The main findings after trochlear nerve sectioning were (1) the amplitude and peak velocity of torsional quick and slow phases of the paretic eye was less than that in the normal eye for both intorsion and extorsion, and (2) the vertical motion of the paretic eye increased during both torsional slow and quick phases. After corrective inferior oblique surgery, both of these effects were even greater.


CONCLUSIONS
Acquired SOP and corrective inferior oblique-weakening surgery create characteristic patterns of change in tOKN that reflect alterations in the dynamic properties of the extraocular muscles involved in eye torsion. tOKN also provides information complementary to that provided by the traditional Bielschowsky head-tilt test and potentially can help distinguish among different causes of vertical ocular misalignment.
Shan
Xiaoyan
X
Department of Neurology, The Johns Hopkins University, School of Medicine, Baltimore, Maryland 21287, USA.
Tian
Jing
J
Ying
Howard S
HS
Walker
Mark F
MF
Guyton
David
D
Quaia
Christian
C
Optican
Lance M
LM
Tamargo
Rafael J
RJ
Zee
David S
DS
D000208:Acute Disease; D000818:Animals; D003714:Denervation; D005260:Female; D008253:Macaca mulatta; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D009801:Oculomotor Muscles / Q000294:innervation / Q000503:physiopathology*; D013285:Strabismus / Q000503:physiopathology*; D014102:Torsion Abnormality / Q000503:physiopathology*; D014321:Trochlear Nerve / Q000502:physiology; D020432:Trochlear Nerve Diseases / Q000503:physiopathology*