Normally, the retina is securely anchored to the choroid layer at the back of the eye. Retinal detachment happens when a blunt or penetrating injury, or other condition allows a hole or tear to develop in the retina. Through the opening fluid collects between the retina and the choroid layer of the eye, causing them to separate.
If you are nearsighted, or have protruding eyes, you are more likely to have retinal detachment, because in these conditions, the retina is more tightly stretched over the back of the eye. Also, if you have had recent cataract surgery, you have a higher risk of retinal detachment.