A simple, essentially non-mathematical, form of presentation has been adopted describing and explaining all that is necessary for the clinical routine of refraction. Its object is fundamentally practical and, while theoretical matters are dealt with sufficiently to make their application understandable, no attempt has been made to enter into the mathematical foundations or formulae of the subject. This edition includes several new topics regarding the direction which clinical optics is taking allowing for sensible answers about, for example, the prospects of corrective surgery for refractive errors. The contribution on contact lenses is deliberately basic enough to acquaint those outside with problems which might present in general ophthalmic consultation.