Correspondence PAROXYSMAL OCULAR DOWNWARD DEVIATION
To the Editor: The description of the eye movement in the report entitled
Paroxysmal Ocular Downward Deviation in Neurologically Impaired Infants by Yokochi  is very similar to that of ocular bobbing, specifically atypical ocular bobbing . Atypical ocular bobbing is characterized by rapid, relatively conjugate downward deviation of the eyes with superimposed convergence, sometimes making a full excursion. The eyes may remain down for as long as 10 s and then drift slowly back to midposition. Horizontal eye movements are partially or completely preserved in atypical ocular bobbing but not in typical ocular bobbing. The cycle of a fast downward eye movement followed by a slow return to mid position, also called V bobbing , may repeat itself in an irregular fashion every 5-30 s. It occurs most commonly in patients with metabolic encephalopathy but also occurs with several other extra-pontine lesions, such as cerebellar hemorrhage. The superimposed convergence of the V pattern is most likely the result of the tertiary action (adduction) of the inferior recti muscles and is mediated either by overaction of the inferior recti or underaction of their antagonists, the inferior oblique muscles. Atypical bobbing usually suggests a poor prognosis but has been described in conscious and partially conscious patients who have survived. Dr. Yokochi's patients obviously had severe bilateral cerebral hemisphere damage but intact pontine function, compatible with some causes of atypical ocular bobbing. Troost and Hitchings recently reviewed the different types of ocular bobbing  The term, tonic downward deviation, of the eyes describes another phenomenon albeit in the same spectrum, but with different implications . Dr. Yokochi's report of atypical or V ocular bobbing in neurologically impaired in-
478 PEDIATRICNEUROLOGY Vol. 8 No. 6
rants is an important contribution, but a new name is nol necessary. Patrick Lavin, MD Vanderbilt University Medical Center Nashville, Tennessee
References  Yokoehi K. Paroxysmal ocular downward deviation in neurologically impaired infants. Pediatr Neurol 1991;7:426-8.  Susac JO, Hoyt WF, Daroff RB, Lawerence W. Clinical spectrum of ocular bobbing. J Neurol Neurosurg Psychiatry 1970;33: 771-5.  Troost BT, Hitchings L. Eye movements in loss of consciousness (stupor, coma). Bull Soc Belge Ophtalmol 1989;237:20%26.  Lavin PJM. Eye movement disorders and diplopia. In: Daroff RB, Fenichel GM, Marsden CD, Bradley WG, eds. Neurology in clinical practice. Boston: Butterworth, 1991 ;633,638-9.
To the Editor: I am grateful to Dr. Lavin for his valuable comments. He suspects that paroxysmal ocular downward deviation is similar to atypical and V ocular bobbing. The abnormal eye movement in my report differs from ocular bobbing. The reported eye movement has fast downward movement tbllowed by slow return, the same as that occurring in ocular bobbing. The downward movement does not repeat, but occurs only a few times per minute in exceptional cases. The ocular downward movement and the downward movement of the upper eyelids occur at the same time in every case. These two characteristics distinguish ocular downward movement in my report from ocular bobbing. Kenji Yokochi, MD Seirei-Mikatabara General Hospital Shizuoka, Japan