Visual processing speed deficits in multiple sclerosis

Multiple Sclerosis (MS) is an inflammatory demyelinating disease, which usually affects adults between the ages of 20 and 50. Both at its initial stages and during the course of the disease, acute episodes of neuro-ophthalmic syndromes are frequent, and have been associated with long-term abnormalities in the visual system, even when full clinical recovery is reached. Moreover, recent studies have also reported visual system abnormalities in MS individuals without a previous history of acute episodes of neuro-ophthalmic syndromes, thus suggesting that the visual system might be vulnerable to MS. Cognitive deficits are equally frequent in MS and appear both at the initial and later stages of the disease’s progression. Processing speed is probably one of the most common cognitive deficits in MS. Despite the fact that both visual abnormalities and cognitive impairment are common in MS, the complex interaction between these two is not completely understood. The current study aims to contribute to a further understanding of the interaction between these types of impairments by assessing visual processing speed deficits in relapse-remitting MS (RRMS). Specifically, it is our objective to understand whether the history of neuro-ophthalmic syndromes might be related with worse performances in vision-based processing speed tasks in RRMS participants with normal or corrected-to-normal visual acuity. Additionally, we propose to study how putative abnormal temporal properties of visual processing might be related with processing speed deficits, which was assessed through neuropsychological and psychophysical tasks. In the first study, results suggest that having a history of the neuro-ophthalmic syndromes is related with poor performance in vision-based processing speed tasks. MS individuals with a history of neuro-ophthalmic syndromes still present, however preserved capability to perform visual tasks. Since long-term abnormalities often occur after this clinical event, we hypothesized that visual system defects might contribute to visual processing speed deficits, commonly found in MS. In the second study, it was demonstrated that processing speed deficits were associated with a decreased capability to detect fast presentations of visual stimuli, as well as with a higher limitation in temporal processing capacity. Moreover, the temporal dynamics of visual processing seem to be compromised, on average, for participants with multiple sclerosis, regardless of their cognitive performance. For instance, for multiple sclerosis participants with processing speed deficits, the problem seems not to be an impaired capacity to perform a recognition task or process visual information, but rather lower temporal processing capacity of the visual system. These results might be an expression of a latent sensorial temporal limitation of the visual system in participants suffering from relapse-remitting multiple sclerosis, perhaps contributing significantly to the processing speed deficits found. The potential neural causes for the presented results will be discussed. Furthermore, implications for rehabilitation and future studies will also be presented. Défices de velocidade de processamento visual na Esclerose Múltipla