Patent Blue V (Acid blue 1), a biological dye, serves as an intraocular stain in retinectomy—surgical removal of the inner limiting membrane (ILM). Its use facilitates the complete excision of premembrane structures in vitreoretinal surgeries. Spectral analysis reveals that Patent Blue V absorbs strongly below 450 nm and above 600 nm, exhibiting a blue-green hue. Additionally, it functions as a tracer in lymphangiography to guide the surgical removal of cancerous lymph nodes [1][2].