Cortical Visual Connections via the Corpus Callosum are Asymmetrical in Human Infantile Esotropia.

PURPOSE: Besides chiasmal hemidecussation, interhemispheric connections are likely important in human binocularity. The corpus callosum (CC) is the major fiber bundle in the mammalian brain which mostly connects homologous cortical areas in the two hemispheres. Visual interhemispheric connections were found abnormal in strabismic cats. No studies have investigated these pathways in humans with infantile strabismus. METHODS: Diffusion tensor imaging was used in four subjects with infantile esotropia (IE) and nine control subjects with normal binocularity, in order to study interhemispheric fibers in the CC connecting the right and left primary visual cortical areas. RESULTS: The number of callosal fibers linking both visual cortical areas between the hemispheres was found to be higher in subjects with IE. Also in IE, the amount of visual callosal fibers found after analysis from the primary visual cortical areas on one side appeared significantly different from the amount starting from the contralateral primary visual areas. The distribution area on one side is wider. CONCLUSION: We show callosal visual fibers to be abnormal in human IE. Subjects with IE showed abnormal numbers of transcallosal fibers connecting the visual cortical areas on both sides which likely results from an abnormal elimination process during development. Pruning of these fibers in IE favors the side of the visual cortex ipsilateral to the dominant eye. This study underlines the likely role of the CC in the development of human binocularity.

Retinal nerve fiber layer thickening in ARSACS carriers.

PURPOSE: Two Caucasian Belgian families were diagnosed with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). The ophthalmological findings in both ARSACS disease and carriers are described. METHODS: In addition to a complete ophthalmological assessment, in both patients and carriers, spectral-domain Optical Coherence Tomography scans of the peri-papillary retinal nerve fiber layer were performed. RESULTS: Molecular analysis revealed a missense mutation which has not been reported before. Besides patients with ARSACS, who also presented additional ophthalmological abnormalities i.e. eye movement problems, ARSACS carriers demonstrated thickening of the retinal nerve fiber layer. CONCLUSION: The most conspicuous ophthalmological feature of ARSACS is an increased thickness of the peri-papillary retinal nerve fiber layer. Retinal striation and thickening of the nerve fiber layer on spectral-domain Optical Coherence Tomography appeared also in carriers of the ARSACS-gene. Other ophthalmological features encountered, were gaze-evoked nystagmus and rebound nystagmus.

Breast Cancer Metastasis Presenting as Conjunctival Chemosis.

A 72-year-old woman presented with a painful right eye. A few weeks before, she had noticed a red, swollen area in the conjunctiva of the same eye. On slit lamp examination, it appeared as chemosis and vascular injection; artificial tears were prescribed. A month later, a firm mass developed on the superotemporal orbital rim, in the area of the lacrimal gland. A CT scan revealed infiltrative structures in both the left and right orbit, with contrast staining in the right lacrimal gland and near the left optic nerve. A biopsy was taken of the conjunctival swelling as well as of the lacrimal gland. Both tissues showed infiltration with lobular breast carcinoma metastases.

Does dominance of crossing retinal ganglion cells make the eyes cross? The temporal retina in the origin of infantile esotropia ­ a neuroanatomical and evolutionary analysis.

A closer look at the evolution of the eye and the brain provides a possible explanation for both the origin of infantile esotropia and its motor characteristics. In the course of evolution, the eyes have moved from a lateral to a frontal position. Consequently, the monocular visual fields started to overlap resulting in a binocular visual field. In lateral-eyed animals, the retinae project to the contralateral visual cortices only. These projections are also found in binocular mammals and birds with binocular visual fields but in addition there are uncrossed projections from the temporal retinae to the visual cortex. The partial chiasmal decussation and the corpus callosum provide the necessary structure that allows binocular vision to develop. Disruption of normal binocular development causes a loss of binocularity in the primary visual cortex and beyond. Beyond the primary visual cortex, the contralateral eye dominates while the temporal retinal signal appears to lose influence. Loss or absence of binocular vision in infantile esotropia may be caused by inadequate retinotopic matching between the nasal and temporal retinal signals like in albinism with an abnormal or asymmetric chiasmal decussation or agenesis of the corpus callosum. Dominance of the crossing retinal signal might also explain the motor characteristics of infantile esotropia (asymmetric OKN, latent nystagmus, DVD). A normal binocular cortical signal will predominate over the evolutionary older, originally non-binocular, retinal projections to the superior colliculi (CS) and the accessory optic system (AOS). A suppressed temporal retinal signal paves the way for the re-emergence of eye movements driven by one eye, as in lateral-eyed non-binocular animals.

A hypothetical mechanism for DVD: unbalanced cortical input to subcortical pathways.

Dissociated vertical divergence (DVD) is commonly encountered in the infantile strabismus syndrome. The movement is said to be dissociated since alignment differs between right and left eye fixation. It has been hypothesized that DVD is caused by a primitive reflex present in fish. Visual pathways in the fish brain indeed are dissociated with complete crossing at the optic chiasm and projection to the superior colliculus instead of a visual cortex. Neuroanatomical data and clinical characteristics of DVD, however, contradict this hypothesis. From these data a new hypothesis arises: corticotectal lateralization. The absence of binocular development in the cerebral cortex in infantile strabismus gives rise to dissociated activation of subcortical pathways through individual less tightly linked colliculi.