The sub-clinical see-saw nystagmus embedded in infantile nystagmus.
A transient, decompensated vertical phoria in an individual with infantile nystagmus syndrome (INS) resulted in two images that oscillated vertically-a diplopic oscillopsia. Ocular motor studies during the vertical oscillopsia recreated by vertical prisms, led to the identification of a sub-clinical see-saw nystagmus (SSN), present under the prism-induced diplopic condition. Retrospective analysis of ocular motor recordings made prior to the above episode of vertical diplopia revealed the presence of that same sub-clinical SSN. The SSN had not been detected previously despite extensive observations and recordings of this subject's pendular IN over a period of forty years. Three- dimensional search-coil data from fourteen additional INS subjects (with pendular and jerk waveforms) confirmed the existence of sub-clinical SSN embedded within the clinically detectable horizontal-torsional IN in seven of the fifteen and a sub-clinical, conjugate, vertical component in the remaining eight. Unlike the clinically visible SSN found in achiasma, the cause of this sub-clinical SSN is hypothesized to be due to a failure of the forces of the oblique muscles (responsible for the torsional component of the IN) to balance out the associated forces of the vertical recti; the net result is a small, sub-clinical SSN. Thus, so-called "horizontal" IN is actually a horizontal-torsional oscillation with a secondary, sub-clinical SSN or conjugate vertical component. The suppression of oscillopsia by efference copy in INS appears to be accomplished for each eye individually, even in a binocular individual. However, failure to fuse the two images results in oscillopsia of one of them.
Dell'Osso
L F
LF
Daroff-Dell'Osso Ocular Motility Laboratory, Louis Stokes Cleveland Department of Veterans Affairs Medical Center, CASE Medical School, 10701 East Boulevard, Cleveland, OH 44106, USA. lfd@case.edu
Jacobs
J B
JB
Serra
A
A
D004172:Diplopia / Q000209:etiology*; D053483:Eye Movement Measurements; D005133:Eye Movements; D005403:Fixation, Ocular; D006801:Humans; D008297:Male; D008875:Middle Aged; D020417:Nystagmus, Congenital / Q000150:complications / Q000503:physiopathology; D009759:Nystagmus, Pathologic / Q000150:complications* / Q000503:physiopathology; D011446:Prospective Studies; D012189:Retrospective Studies; D014102:Torsion Abnormality / Q000209:etiology