The present study demonstrated that integrity of anterior visual pathways based on OCT metrics was associated with ambulatory outcomes in persons with MS. Those who had reduced TMV, in particular, walked a shorter distance during the 6MW and slower during the T25FW, independent of disease duration, EDSS, and age in the GEE models. Collectively, this research indicates that OCT metrics of anterior visual pathway integrity, particularly TMV, are associated with functional consequences, namely, reduced ambulatory performance, in MS. This might position OCT and its metrics as an important outcome for inclusion within rehabilitation research of walking function; such metrics might provide indications of possible neuroprotective and neuroreparative consequences of rehabilitation based on integrity of the anterior visual pathway.
Researchers have previously reported associations between OCT metrics and EDSS as well as MSFC scores in persons with MS [19
]. This is important as both the EDSS and MSFC include ambulatory measures of the 500-meter walk and T25FW, respectively, when generating an overall score. Such observations, in part, motivated our interest in examining the associations between RNFLT and TMV with ambulatory outcomes, and controlling for covariates, particularly EDSS scores. To that end, our results indicate an association between TMV and both 6MW and T25FW performance, independent of EDSS as well as age and MS duration. Accordingly, this is the first study, to our knowledge, that has reported an independent association between OCT metrics of anterior visual pathway integrity and ambulatory performance in persons with MS.
The mean values of RNFLT, TMV, T25FW, and 6MW of persons with MS (without optic neuritis or any other ocular diseases) in the present study were consistent with those in previous researches [19
]. For example, the mean (SD) RNFLT in the present study was 90.9 (14.9)μ
m, and this was consistent with the value of 95.6 (14.5)μ
m from a previous research [23
]. The same consistency in mean values is seen with TMV [23
]. Regarding ambulatory function, the T25FW and 6MW values of 6.9 (3.5) seconds and 1,336 (441) feet, respectively, are consistent with the values of 6.4 (2.7) and 1,277 (255) in previous researches [19
]. Such observations are important for contextualizing our sample and results within the broader research on OCT metrics and ambulatory function involving persons with MS.
The integrity of the anterior visual pathway might be associated with ambulatory performance as vision is coupled with walking. Indeed, vision and gait are two of the most important bodily functions that are compromised, yet highly valued, across the early and late phases of MS [7
]. Visual dysfunction has further been identified as one of several possible impairments (e.g., weakness, sensory loss, and ataxia) that might influence walking in neurological diseases including MS [9
]. Overall, we are not surprised that integrity of the anterior visual pathway is a correlate of walking—another global indicator of MS progression—and this study provides the first data supporting the presumed association between visual and walking functions in MS [9
We believe that one possible implication of our study is that OCT metrics might be included in rehabilitation trials for understanding adaptations within the CNS that correspond with improvements in ambulatory function. Indeed, rehabilitation interventions that improve gait in MS might do so, in part, through neuroreparative and neuroprotective processes. If correct, then OCT metrics might be considered for inclusion in clinical trials of rehabilitation approaches for improving ambulation in people with MS. Such an approach provides simple, affordable, and noninvasive metrics for documenting possible neuroreparative and neuroprotective outcomes.
There are many strengths of the current study including the first examination of anterior visual pathway metrics and walking function controlling for EDSS and other covariates in MS. There are important limitations of the current study. The most important limitation is that the study included time-domain OCT, and this has poor resolution and reduced accuracy of outcomes. This would seemingly bias any associations with other outcomes towards the null and could be overcome in future research using spectral domain OCT and better characterizing associations with ambulatory outcomes. We do not have data from spectral domain OCT for addressing this limitation in the current study. The sample size might be considered small, but it is sufficient for a preliminary examination of OCT metrics and ambulation. The sample mostly had relapsing-remitting MS, and this limits the generalizability of our data and results amongst those with progressive MS. The study included a cross-sectional design and did not provide data on changes in OCT metrics and ambulatory outcomes over time. Lastly, the T25FW was performed on a carpeted surface, and this differs from the typical administration on a noncarpeted walkway [21
]. This might have reduced walking speed on the T25FW. Despite those limitations, we are excited by the novel data indicating that OCT metrics of anterior visual pathway integrity are associated with walking outcomes in MS.