The macular hole formation takes place in the centre of the retina. A closure of the macular hole is believed to take place if the central retinal area is kept dry in the postoperative period. Therefore the eye is filled with a gas mix and the patients are urged to avoid the supine position in the first postoperative days. The investigators use the "tennis ball technique" where a tennis ball is fastened in the back of the night shirt in order to help patients compliance in avoiding the supine sleeping position. The investigators have developed a positioning measuring device which can measure the extent of supine positioning time. Patients are to sleep two nights with the positioning measuring device, one night with a tennis ball in the back of the night shirt and one night without. Hereby the investigators search new knowledge concerning patients compliance and verification of the "tennis ball technique".