A blowout fracture is a fracture of the floor (or wall) of the orbit (eye socket). This is caused by trauma to the eye with a blunt object such as a fist, knee or cricket ball. The force of a blow distorts the orbit and raises pressure within it.
The raised pressure causes thin bone of the floor (or medial wall) to blowout and fracture. This may result in structures in the orbit protruding into the surrounding sinuses. If the muscles which move the eye are caught in the fracture the eye would move with the other eye resulting in diplopia (double vision). If large, the eye may sink back and down (enophthalmos). Investigation is with a CT scan X-ray.