In search for a magnocellular deficit in Optic Neuritis patients

Abstract

Optic neuritis (ON) is an acute inflammatory disease of the optic nerve. Following visual acuity recovery, several patients report visual discomfort although ophthalmologic assessments show a complete recovery. To evaluate what could induce these complaints, the present study investigates visual processing of healthy individuals and patients with recovered ON. Specifically, magnocellular pathway was assessed. Two types of visual tasks were administered in monocular vision to two different groups of controls and patients. First, 18 controls and 7 patients(4 left ON, 3 right ON) had to detect and categorize low(LSF) or high(HSF) spatial-frequency scenes to assess magno- or parvocellular pathways. Then, performance of 16 controls and 5 patients (4 left ON, 1 right ON) were recorded while performing a denomination task of forms and moving objects (Objects From Motion). These objects could only be perceived by a contradictory movement of black and white dots and mainly require the implication of the magnocellular pathway. Patients showed normal visual analysis in low spatial frequency scenes compared to controls, but had difficulties in naming OFM with their affected eye (AE) (F(1,19)=17.47;p<.01). However, in scenes analysis, controls were faster for LSF than HSF (F(2,34)=6.78;p<.01), but this “coarse-to-fine” pattern was not found in patients, revealing a slower processing of LSF with their AE. As magnocellular pathways preferentially process LSF and motion stimuli, the current results suggest its impairment following ON, explaining patients' visual discomfort. In addition, given the dissociation between the preserved performance in visual scene detection and categorization and the difficulty in naming OFM, motion processing appears to be a more sensitive measure to evaluate patients' deficits. Given that results cannot be explained by ophthalmologic considerations, they argue in favor of a possible functional reorganization in higher visual areas.

Footnotes

 This work was supported by Foundations Edmond and Benjamin de Rothschild (Genève, Switzerland and New York, USA).