The vitreous is the clear jelly like mass in the posterior chamber of the eye which fills the space between the lens and the retina. The vitreous goes through three phases in its development with formation of the primary, secondary and tertiary vitreous respectively.
The primary vitreous forms as a large blood vessel which starts from the back of the eye and grows forward towards the lens. At the back of the lens this vessel, the hyaloid artery divides many times to form a network of blood vessels around the lens, known as the tunica vasculosa lentis. These blood vessels subsequently disappear before birth. Sometimes these blood vessels fail to degenerate, remaining in the eye after birth to form a large vascular plaque over the back surface of the lens. This condition is known as a persistent hyperplastic primary vitreous.
This disease is suspected to be heritable at least in the English Staffordshire and the Doberman in which the condition was first described. It can cause vision problems but most cases are operable to restore vision. Since this is a vascular structure there is some risk however of haemorrhage within the eye during surgery.