**2. Retinal histopathological studies in amyotrophic lateral sclerosis patients and experimental models**

ALS is a neurodegenerative disease, which shares some pathophysiological mechanisms common to other diseases of the CNS, such as vascular pathology, glutamate excitotoxicity, fragmentation, aggregation, and functional abnormalities of the mitochondria, impaired retrograde and anterograde axonal structure and transport,

increased free-radical and oxidative stress, protein aggregation, and neuroinflammation [12, 58–61]. However, studies in the retina are scarce and have focused only on four such mechanisms, as described below.
