Glaucoma and Systemic Neurodegenerative Diseases: The Brain–Eye Continuum

Glaucoma is a chronic, progressive optic neuropathy characterized by retinal ganglion cell (RGC) death and visual field loss.It is the leading cause of irreversible blindness globally, affecting more than 70 million people, and its prevalence is expected to rise with aging populations.Traditionally, glaucoma was defined primarily as a disease of intraocular pressure (IOP) dysregulation, but recent decades have reframed it as a complex neurodegenerative disorder involving multiple systemic and local risk factors.In parallel, systemic neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS) pose immense healthcare and socioeconomic burdens.The concept of the "eye as a window to the brain" arises from the fact that the retina and optic nerve are direct extensions of the central nervous system (CNS).This has positioned the eye as a valuable site for studying neurodegenerative processes noninvasively, using advanced imaging modalities such as optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA).Glaucoma is a chronic neurodegenerative optic neuropathy, and the concept of the "eye as a window to the brain" highlights its overlap with systemic diseases such as AD, PD, and MS.