Fluorescein sodium salt is widely used in medical diagnostics, particularly in ophthalmology. It is applied as a fluorescent dye to detect corneal abrasions, ulcers, and foreign bodies in the eye. When administered as eye drops, it highlights damaged areas under blue light, aiding in the diagnosis and treatment of eye conditions.

In addition to ophthalmology, it is utilized in angiography to visualize blood flow in the retina and choroid. This helps identify abnormalities such as leaks, blockages, or swelling in the blood vessels.

Beyond medical applications, fluorescein sodium salt is employed in environmental studies to trace water flow and detect leaks in plumbing systems. Its bright fluorescence makes it an effective tracer in hydrology and engineering projects.

In microbiology, it is used as a staining agent to study cell structures and processes under a fluorescence microscope. Its versatility and strong fluorescence make it a valuable tool across various scientific and medical fields.