The paracentral visual field in multiple sclerosis: evidence for a deficitin interneuronal spatial summation?

A visual complaint such as blurred or 'washed-out vision' can be one of the early signs of multiple sclerosis (MS). Although visual deficits are commo nly attributed to optic nerve demyelination even with preserved visual acui ty, the results of a considerable number of visual studies are inconsistent with this interpretation [Camisa, Mylin, & Bodis-Wollner, Annals of Neurol ogy 10 (1981) 532-539; Regan & Neima, British Journal of Ophthalmology 68 ( 1984) 310-315]. However, a retinal axonal (nerve fiber layer) defect can be detected in some eyes, this is not the rule. Routine visual field (VF) tes ts, with a low sampling rate may also be non-informative in MS and optic ne uritis, possibly because the VF abnormalities may be small and spotty or th ey can be found between tested points. The present study combined the advan tages of VF and contrast sensitivity (CS) testing by applying contrast peri metry (CP), to the central 16 degrees of the VF. Four paracentral VF quadra nts were tested in clinically affected and unaffected eyes of 31 MS patient s and 26 controls. The stimuli were vertical Gaussian apertured sinusoidal gratings (Gabors) of 1 cpd. CS was obtained as a function of the diameter o f the Gabor ranging from 1 to 7.4 degrees. The CP data of controls and defi nite and probable MS groups were significantly different for each pattern s ize, but the largest difference was found at diameters 2.5-3.7 degrees. Our study adds to previous evidence showing that optic nerve pathology does no t explain 'subclinical' and manifest visual dysfunction in MS. Given previo us studies revealing orientation dependent monocular visual deficits and ou r study results, parsimony suggests that MS affects a network relying on my elinated lateral axonal branches of the visual cortex, binding monocular co lumns of neurons with like-with-like specificity. (C) 2001 Elsevier Science Ltd. All rights reserved.