This textbook has been written for ophthalmologists undertaking their membership and fellowship examinations and for orthoptic undergraduate students. Qualified orthoptists, general ophthalmologists and optometrists should 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 one 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 two and three outline the various types of concomitant and incomitant strabismus and ocular motility disturbances and the application of orthoptic investigation. Section four, 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.