Eye Diseases and Conditions Slideshow Pictures Pink Eye Slideshow Pictures Laser Eye Surgery Pictures 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 How's Your Eye Health?Diabetes and Your EyesEye Care for Diabetes Featured Centers How Is Your MS Care Routine? Assess Yourself Health Solutions From Our Sponsors Kept Your Wisdom Teeth? What is TAVR?