Fig. 1

Progression of retinal degeneration. The healthy retina consists of five major classes of neurons: photoreceptors, bipolar cells, retinal ganglion cells, horizontal cells, and amacrine cells, as well as the non-neuronal pigment epithelium. The early, intermediate, advanced, and late-stage of the retinal degenerative process results in changes in the function and morphology of the retina over time. These changes include truncation of the outer segments of PRs, reduction in cell numbers due to cell degeneration and death, appearance of reactive glial cells, hypertrophy of Müller cells, migration of neuronal cells, translocation of amacrine and bipolar cells into other layers, deep synaptic change, cell death progresses, the absence of visual capacity, deterioration of blood-retinal barrier and disruption of RPE and Brunch's membrane. The current therapeutic approaches have also been presented for each degeneration phase