Vitreomacular traction (VMT) is caused by an abnormal posterior vitreous detachment (PVD). The vitreous gel lies inside the eye and provides support for the eye to develop properly. As we age, the vitreous gel naturally weakens and breaks down.
At some point in life, a PVD will occur when the vitreous gel collapses away and separates from the retina. In VMT there is an abnormally strong attachment between the macula (part of the retina responsible for central vision) and the vitreous. This stops the separation and instead causes pulling on and distortion of the macula.