Fluorescein is widely used in ophthalmology as a diagnostic tool. It is applied as a dye in eye examinations to detect corneal abrasions, ulcers, and foreign bodies. When applied to the eye, it highlights abnormalities under cobalt blue light, making it easier for healthcare professionals to identify and assess eye conditions.

In addition to its medical applications, fluorescein is utilized in environmental studies to trace water flow. It is introduced into water systems to monitor the movement and dispersion of water in rivers, streams, and groundwater. This helps in understanding water pathways and detecting leaks or contamination sources.

Fluorescein is also employed in forensic science to detect latent bloodstains. When sprayed on suspected areas, it reacts with the iron in hemoglobin, causing blood traces to fluoresce under UV light. This aids investigators in identifying evidence that is not visible to the naked eye.

Furthermore, it serves as a fluorescent marker in biological research. Scientists use it to label and track cells, proteins, or other molecules in experiments, enabling the visualization of biological processes under a microscope.

Additional medical uses include intravenous administration for fluorescein angiography to evaluate retinal blood flow and in urology to detect urinary tract fistulas. Its versatility and strong fluorescent properties make it a valuable tool across various fields, from medicine to environmental science and research.