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Avery H Weiss, James O Phillips, John P Kelly; Infantile Nystagmus and Abnormalities of Conjugate Eye Movements in Down Syndrome: A Corollary of Cerebellar Maldevelopment. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2913.
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© ARVO (1962-2015); The Authors (2016-present)
Anatomic and neuroimaging evidence of abnormal cerebellar development in humans and a mouse model of DS prompted us to study the eye movements of DS patients with CN.
Gaze-holding in primary gaze and at eccentricities of 15 degrees, saccades to horizontal or vertical target steps ranging from 5 to 25 deg, smooth pursuit of targets drifted at 10, 20 & 30○/s and optokinetic nystagmus(OKN) in response to horizontally-oriented square wave gratings (0.1cpd) drifted at 15 ,30 and 45○/s were recorded with binocular video-oculography (SMI, Interacoustics).
All patients demonstrated one or a combination of the following gaze holding instabilities: 1) Conjugate, horizontal, constant velocity, jerk nystagmus; 2) Conjugate, horizontal symmetric or asymmetric pendular nystagmus; 3) Intermittent saccadic oscillations that could be larger in one eye, or symmetric in both eye; 4) saccadic oscilations superimposed upon nystagmus types 1 or 2. Gains for horizontal saccades to target steps of more than 5 deg were uniformly hypometric (Gains = 0.50-0.78 compared to >0.80 for age-matched norms). The relationship between peak saccadic velocity and saccade amplitude followed the main sequence. Gains for vertical OKN were asymmetric in a subset of children.
The nystagmus and abnormalities of conjugate eye movements observed in children with DS are consistent with functional abnormalities of the cerebellum. The findings of dysmetric saccades that follow the main sequence localize the underlying abnormality to the cerebellum and exclude brainstem structures. Sonic Hedgehog has been shown to mediate the proliferation and anatomical organization of cerebellar granule neuronal precursor cells. Deregulation of Sonic Hedgehog in DS may account for the cerebellar abnormalities that underlie the congenital nystagmus and ocular motor abnormalities.
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