Melanin is a natural glare-reducing agent present in the human eye that protects it from sunlight damage. 90% of the light that enters the eye is absorbed by Melanin. So, basically the role Melanin plays in "eye protection" is critical. Each person has a different quantity of Melanin, so for example, brown eyes have more than blue eyes.
Mell.a.nin / melanin / n. dark brown to black pigment of occurring in the hair, skin, and iris of the eye. Melanin is naturally occurring pigment found throughout the human body that helps determine such physical characteristics as hair and skin color.
Melanin in the eye, however, plays a much more essential role, both protecting against damage and aiding visual acuity. Melanin located in the iris filters harmful light, melanin found in the eye protects sensitive retinal tissue.