Vitreous: A clear, jelly-like substance that fills the middle of the eye. Also called the vitreous humor, "humor" in medicine referring to a fluid (or semifluid) substance. From Eye Health Resources IRD: The Importance of Early Diagnosis12 Devices That Can Help Your Low VisionTreatments for Wet AMD Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors