Visual loss can be partial (meaning the vision is impaired or hazy or that the visual field is reduced) or complete (meaning all or part of the vision in one or both eyes is too poor for useful function). It may occur with or without pain, suddenly or gradually. All of these aspects depend on the cause. Some, but not all, visual loss is permanent and some, but not all, can be prevented.
This is a companion discussion topic for the original article at https://patient.info/eye-care/visual-problems