Interconnection between brain and retinal neurodegenerations

The eye is a special sensory organ, which is basically an extension of the brain. Both are derived from neural tube and consist of neurons. Therefore, diseases of both the brain and eye should have some similarity. Neurodegenerative disorders like Alzheimer's disease (AD) is the major cause of dementia in the world. Amyloid deposition in the cerebral cortex and hippocampal region is the basic pathology in AD. But along with it, there are various changes that take place in the eye, i.e., abnormal pupillary reaction, decreased vision, decreased contrast sensitivity, visual field changes, loss of retinal ganglionic cells and retinal fiber layer, peripapillary atrophy, increased cup-disk ratio, retinal thinning, tortuosity of blood vessels, and deposition of Aβ-like substance in the retina. And these changes are present in the early part of the disease when only mild cognitive impairment is there. As the brain is covered by a hard bony skull which makes it difficult to directly visualize the changes occurring in the brain at molecular levels, finer details of disease progression are not available with us. But the eye is the window of the brain; with advanced modern techniques, we can directly visualize the changes in the retina at a very fine level. Therefore, by depicting neurodegenerative changes in the eye, we can diagnose and manage AD at very early stages. Along with it, retinal neurodegenerations like glaucoma and age-related macular degeneration (ARMD) are the major cause of loss of vision, and still, there are no effective treatment modalities for these blinding conditions. So if we can understand its pathogenesis and progression by correlating with brain neurodegenerations, we can come up with a better therapy for glaucoma and ARMD.