Whether the damage done by amyotrophic lateral sclerosis (ALS) also affects visual pathways, namely the macula, is a matter of debate among scientists and physicians. Researchers at the Feinberg School of Medicine investigated this, comparing the macular structure of ALS patients and examining its correlation with pulmonary function tests, and concluded that macular degeneration was evident in patients and might even serve as a biomarker of disease severity and progression.
The study, “Macular sub-layer thinning and association with pulmonary function tests in Amyotrophic Lateral Sclerosis,” published in Scientific Reports, indicates that the retinal structure is involved in ALS and that thinning of the macula — a small part of the retina involved in central vision and detail definition — correlates with pulmonary function tests and is a possible disease biomarker.
A hallmark of ALS is degeneration of upper and lower motor neurons. However, recent studies show evidence of cognitive impairment and degeneration of non-motor systems in ALS, and ocular motor dysfunction has been described in patients but inconsistently.
Although not a prominent feature in ALS, decreased visual acuity and poor contrast sensitivity in ALS point to the existence subclinical structural defects in the anterior visual pathway. Such findings and the lack of consensus regarding them led the researchers to assess macular changes, using optical coherence tomography (OCT) imaging, in ALS patients and compare them to healthy controls. Pulmonary function tests and time since symptom onset were collected retrospectively to assess if retinal degeneration would correlate with measures of disease severity.
According to results, macular retinal nerve fiber layer was significantly thinner in ALS patients. Moreover, the nerve fiber layer thickness positively correlated with two measures of pulmonary function: forced vital capacity percent predicted (FVC%) and forced expiratory volume in 1 second percent predicted (FEV1%). Researchers agree that these results suggest that retinal nerve fiber layer thinning may be a quantitative biomarker of ALS-related neurodegeneration, useful for following disease progression.
“Analysis of OCT measurements supports the involvement of the anterior visual pathway in ALS. Subtle structural thinning in the macular retinal nerve fiber layer correlates with pulmonary function tests,” the researchers said.
“Visual function tests such as contrast sensitivity, which has been shown to correlate with [retinal nerve fiber layer thinning] in [multiple sclerosis], may prove capable of detecting retinal dysfunction that precedes structural changes and should be considered in future studies. Such tests may also be useful, along side OCT imaging and standard neurologic examination, for disease screening and severity stratification,” they concluded.