This is the clear gel that fills the back of the eye. When you are born it completely fills this space and is attached to the photographic lining of the eye known as the retina. As you age the gel dissolves and shrinks.
Problems with the gel are related to the accumulation of debris within the gel (floaters), and the natural separation of the gel from the retina (vitreous detachment). This may cause a sudden increase in floaters or may stretch (macular traction) or tear (macular hole) or scar (epiretinal membrane) structures within the eye. A stretched retina may cause blurring or distortion of vision.
Floaters & Flashes
Vitreous traction creating retinal holes and wrinkles