How the Eye Works - The Basics
The eye can be thought of as similar to a camera, with two main parts, a lens and a film. The film layer is called the retina and lines the back wall of the eye. There is a gel called the vitreous that is located in front of the retina and is very firmly adherent to it. As we start to get older, the vitreous slowly separates from the back wall of the eye and moves towards the front of the eye. This process is called a vitreous detachment. A horse shoe tear occurs when the gel pulls very firmly on the retina and creates a full-thickness tear in the retina, while still remaining attached to one edge (see photo).