Melanopsin retinal ganglion cell loss and circadian dysfunction in Alzheimer's disease (Review)

Alzheimer's disease affects 27 million individuals and is the most common cause of dementia worldwide. The pathology of Alzheimer's disease is primarily due to the β-amyloid deposits and neurofibrillary tangles. These deposits exist largely in the cerebral blood vessels, but have also been shown to exist in retinal vessels. A new class of cells that were recently identified, known as melanopsin-expressing retinal ganglion cells (mRGCs), are involved in the non-image forming functions of the eye. These functions include circadian activities such as temperature rhythms, melatonin release and rest-activity cycles. Circadian dysfunction has been investigated in many cases of Alzheimer's disease. In this review, we outline the current accepted Alzheimer's disease pathology, the role of mRCGs in optic neuropathies and the role of mRCGs, leading to circadian dysfunction, in Alzheimer's disease.