OPN1SW, also known as short-wave-sensitive opsin 1 or blue-sensitive opsin, is a protein encoded by the OPN1SW gene in humans. This protein is a type of opsin pigment found in the photoreceptor cells of the retina and is crucial for normal color vision, specifically mediating the perception of blue light. It is a G-protein coupled receptor that initiates the visual transduction cascade by converting light into electrochemical signals. The OPN1SW gene is located on chromosome 7q32.1 and is conserved across several species. Defects in this gene can lead to tritan color blindness, a condition where individuals have impaired blue-yellow color vision.