Fluorescein is an orange/red synthetic powder that is soluble in water and alcohol. It has various medical applications, most notably in ophthalmology. When applied topically or injected intravenously, it allows visualization of the retinal and choroidal circulation through fluorescein angiography. This diagnostic technique involves taking photographs at intervals after injection to examine blood flow and detect conditions like macular degeneration and diabetic retinopathy. Fluorescein is also used in tests for corneal abrasions, dry eye, tear drainage problems, and measuring intraocular pressure.