Abstract: That cotton wool spot is focal retinal ischemia and retinal nerve fiber layer infarct could have been read in most ophthalmic textbooks, monographs and journals. Whereas, although retinal ischemia is the most important cause for cotton wool spot, cotton wool spot is not ischemia per se, but localized accumulations of axoplasmic debris within retinal ganglion cell axons owing to axoplasmic flow interruption insulted by many factors including ischemia, mechanic impression and so on. The first part of this article systematically illustrate the etiology, pathological changes, and pathophysiological processes of cotton wool spots formation, in order to improve and clarify the acquaintance. (Ophthalmol CHN, 2024, 33: 401-411)

Key words:  , cotton wool spot, Purtscher flecken, axoplasmic flow interruption, retinal ischemia