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Special Communication |

A Unifying Neurologic Mechanism for Infantile Nystagmus

Michael C. Brodsky, MD1; Louis F. Dell’Osso, PhD2
[+] Author Affiliations
1Departments of Ophthalmology and Neurology, Mayo Clinic, Rochester, Minnesota
2The Daroff-Dell’Osso Ocular Motility Laboratory, Department of Neurology, Case Western University, Cleveland, Ohio
JAMA Ophthalmol. 2014;132(6):761-768. doi:10.1001/jamaophthalmol.2013.5833.
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Lateral-eyed afoveate animals use the subcortical accessory optic system to generate accurate responses to full-field optokinetic input. When humans rotate their eyes to pursue a moving target, the visual world sweeps across their retinas, creating a contraversive optokinetic stimulus. Humans have developed a cortical foveal pursuit system that suppresses the perception of this full-field optokinetic motion during active pursuit. When foveal vision is slow to develop in infancy, this phylogenetically old optokinetic system, which is normally operative in the first 2 months of human life, continues to be ontogenetically expressed. Hypothetically, the incursion on cortical pursuit of the antagonistic motion stimulus from this subcortical optokinetic system facilitates development of the unstable oscillatory activity of the eyes that characterizes infantile nystagmus.

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Figure 1.
Depiction of the Brain, as Viewed From Above, Showing Normal Cortical and Subcortical Projections During Early Human Development

A, Early in infancy, horizontal optokinetic stimuli (shown as leftward or rightward motion) from each nasal retina are transmitted via a subcortical pathway to the contralateral nucleus of the optic tract-dorsal terminal nucleus (NOT-DTN) of the accessory optic system (solid red arrow), which is directionally sensitive to ipsiversive motion (ie, nasalward for the contralateral eye). During this early stage of development, the cortical pursuit pathways (shown as corticofugal projection from the middle temporal area–medial superior temporal area [MT-MST] to the ipsilateral NOT-DTN) have not yet become functional (interrupted green arrows). B, Later in infancy, horizontal optokinetic responses become encephalized, binocular cortical pursuit pathways become fully operational (solid green arrows), and subcortical optokinetic pathways regress (interrupted red arrows). L indicates left eye monocular cells; LGN, lateral geniculate nucleus; R, right eye monocular cells; R+L, cortical binocular cells; SCC, splenium of the corpus callosum; and V1, primary visual cortex. Based on the model proposed by Hoffmann.32

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Figure 2.
Diagram of Cortical and Subcortical Optokinetic Pathways Mediating Infantile Nystagmus

We propose that cortico-mesencephalic-cerebellar pathways involving the middle temporal area–medial superior temporal area (MT-MST), the accessory optic system (AOS), the nucleus of the optic tract, and the flocculus of the cerebellum generate this horizontal oscillation. Pathways for horizontal eye movements are shaded blue, pathways for movements around an oblique horizontal axis are shaded in red, and mossy fiber pathways (unrelated to the climbing fiber pathways mediating the AOS) are shaded in green. Ant C indicates anterior canal; C2, F1, F2, F3, and F4, layers within the cerebellar flocculus; DC, dorsal cap; Front, frontal plane; Hor, horizontal plane; Hor C, horizontal canal; Inf O, inferior oblique muscle; Lat R, lateral rectus muscle; Med R, medial rectus muscle; MT, middle temporal area; MST, middle superior temporal area; NPT, nuclei of the paramedian tracts; NRTP, nucleus reticularis tegmenti pontis; Prep Hyp, nucleus prepositus hypoglossi; Sag, sagittal plane; Sup R, superior rectus muscle; V1, V2, cortical areas; and VLO, ventrolateral outgrowth. Question marks indicate disputed projection of the nucleus of the optic tract to the vestibular nuclei and the NRTP. Modified from Voogd et al.83

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