This textbook has been written for ophthalmologists undertaking their membership and fellowship examinations and for orthoptic undergraduate students. Qualified orthoptists, general ophthalmologists and optometrists will also find it useful as a guide. Orthoptic investigations and the diagnosis and management of strabismus and ocular motility disorders are described, accompanied by numerous illustrations, including equipment. Section 1 gives an outline of the anatomy and innervation of the extraocular muscles, principles and techniques of orthoptic investigative tests and theory of binocular single vision. Sections 2 and 3 outline the various types of concomitant and incomitant strabismus and ocular motility disturbances and the application of orthoptic investigation. Section 4, the appendix, includes many of the orthoptic abbreviations, a glossary of definitions and a number of case histories of strabismus and ocular motility disorders used in practice.