Eye-care physician William Horatio Bates, M.D., (1860-1931) attributed nearly all sight problems to habitual strain of the eyes, and felt that glasses were harmful and never necessary. Bates self-published Perfect Sight Without Glasses and a magazine (and earlier collaborated with Bernarr MacFadden on a correspondence course) detailing his approach to helping people relax such "strain", and thus, he claimed, improve their sight. His techniques centered on visualization and movement. The Bates method is an alternative therapy aimed at improving eyesight. He placed particular emphasis on imagining black letters and marks, and the movement of such. He also felt that exposing the eyes to sunlight would help alleviate the "strain". The efficacy of the method is questionable, and his theory that the eye does not focus by changing the power of the lens, but rather by elongating the eyeball, through use of the extraocular oblique muscles, was contradicted by mainstream ophthalmology and optometry of his day and still is today.