Emmanuel Alain Cabanis

Resolution of homonymous visual field loss documented with functional magnetic resonance and diffusion tensor imaging.

Abstract:A 68-year-old man developed right homonymous hemianopic paracentral scotomas from acute infarction of the left extrastriate area. He was studied over the ensuing 12 months with visual fields, conventional MRI, functional MRI (fMRI), and diffusion tensor imaging (DTI). As the visual field defect became smaller, fMRI demonstrated progressively larger areas of cortical activation. DTI initially showed that the lesioned posterior optic radiations were completely interrupted. This interruption lessened in time and had disappeared by one year after onset. fMRI and DTI are innovative measures to follow functional and structural recovery in the central nervous system. This is the first reported application of these imaging techniques to acute cerebral visual field disorders.

Amblyopie fonctionnelle : évaluation en IRM fonctionnelle de la réponse corticale visuelle après traitement

Objectif Le but de cette etude est d’evaluer la reponse corticale apres stimulation visuelle chez des sujets amblyopes unilateraux apres traitement. Materiel et methodes L’exploration clinique et en IRM fonctionnelle a ete effectuee chez des patients amblyopes unilateraux (7 hommes et 3 femmes, de 21 a 59 ans), traites dans leur enfance pour strabisme. Apres evaluation de l’acuite visuelle actuelle, dix patients furent examines en IRM fonctionnelle. Quatre sessions d’etude monoculaire furent realisees (deux sessions par œil) avec une presentation de damiers noirs-blancs clignotant a des frequences spatiales et temporelles de 1°/8 Hz et 15′/4 Hz. Un realignement anatomique des 4 sessions precedait une analyse statistique (logiciel SPM 99 Statistical Parametric Mapping ® ) mettant en evidence la reponse corticale apres stimulations de l’œil sain et de l’œil amblyope. Resultats et discussion Les reponses corticales visuelles tendent a distinguer deux groupes de patients amblyopes : dans un groupe d’acuite visuelle residuelle superieure ou egale a 7/10 e , la stimulation de l’œil atteint montrait un surcroit d’amplitude de la reponse corticale dans les aires visuelles principales, notamment V1, V3 et V5. Dans le 2 e groupe d’acuite inferieure a 7/10 e , la stimulation de l’œil amblyope induisait une reponse de moindre amplitude dans ces aires. Une activation supplementaire etait notee en regions orbito-frontales, prefrontales, parietales, dans les cuneus et les gyrus linguaux. Ces resultats suggeraient une reponse corticale visuelle differente en fonction de l’efficacite du traitement de l’amblyopie : une acuite visuelle subnormale correspondait a une receptivite corticale amelioree par rapport a la stimulation de l’œil sain, alors qu’une acuite deficiente correspondait a une faible reponse des aires visuelles principales, avec un recrutement d’activation d’aires secondaires dans un processus attentionnel contribuant a la reconstruction de l’image percue. Les effets de la plasticite corticale secondaire au traitement initial de l’amblyopie etaient retrouves meme des annees apres le traitement initial. Conclusion L’etude suggere l’importance d’un traitement efficace et precoce de l’amblyopie dans l’enfance, renforcant la receptivite du cortex visuel primaire et la participation d’aires visuelles secondaires dans un processus attentionnel pour l’analyse du message visuel provenant de l’œil anciennement amblyope.

Imaging in Ophthalmology

The optic pathway extends from the cornea to the visual cortex. It exhibits features that deserve specific neuroradiological investigation. The first characteristic is the anatomical and functional unity of the visual pathway. The second is the differences between child and adult disorders (Ball 1997). In addition, the small size of visual pathways necessitates high-resolution imaging. In children, the presence of leucocoria, an acute or subacute exophthalmia associated with inflammatory signs, may lead to the discovery of retinoblastoma or rhabdomyosarcoma. In adults, lesions of the eyeball may reveal a melanoma or a malignant tumour of the lacrimal gland.

Objective visual field testing with functional magnetic resonance imaging

Purpose : To detect cortical retinotopy using the functional magnetic resonance imaging technique at clinical circumstances. Methods : Four normal volunteers were examined. Four experiments were performed on each subject: a ‘central-peripheral’ visual field stimulation and an ‘upper-lower’ visual field stimulation, both for right and left visual hemifields. The checkerboard stimuli, presented on a front projection screen, subtended 3 degrees of visual angle in height and 5 degrees in width. Sequential paradigms alternated rest phases with no checkerboard stimulation and stimulation phases. For the ‘central-peripheral’ visual field stimulation, the checkerboard was presented to either the central or peripheral visual field. During the ‘upper-lower’ visual field stimulation, the checkerboard was presented to either the upper or lower visual field. Results : The central visual field stimulation revealed a broad activated area in the contralateral occipital pole, whereas the peripheral visual field stimulation displayed a more anterior and narrower activated area. The ‘upper-lower’ visual field stimulation revealed broad activated areas covering the contralateral occipital pole. The upper visual field stimulation revealed the center of the cortical activation located inferiorly to lower visual field stimulation. Conclusion : Retinotopical eccentricity in the primary visual cortex is accurately detected using simple visual stimulations partially presented to the central-peripheral visual field. Upper visual field stimulation bordering the horizontal meridian could be differentiated from lower visual field stimulation in the associated visual cortex. This technique may help to evaluate the visual field.