The retina lines the inside of the eye and is a thin tissue composed of layers of light-sensitive cells which send visual information to the brain. The retina is held in place by the vitreous humour which is a transparent gel composed of water and collagen and lies in the centre of the globe of the eye between the retina and lens. A retinal detachment occurs when the retina pulls away from inside wall of the eye causing loss of vision. This is often due to a hole or tear in the retina produced when the vitreous contracts with the aging process. Trauma may also lead to retinal detachment. The vitreous may also become filled with blood, particularly in association with severe diabetic eye disease where traction may detach localised areas of retina.