Errors of refraction form a major part of teaching of ophthalmology in undergraduates, postgraduate training and optometry. The present book is meant for students appearing for first part of final MBBS that includes both theory and practical in optics. Refraction forms a major part of practical examination in postgraduate evaluation. Students undergoing training for MS, MD, DO, DOMS, FRCS, DNB and degree in optometry will find the book handy for practical and viva. The paramedical ophthalmic assistances will be much benefited from the book. Divided into two parts, i.e., basics of optics and application of optics in clinical ophthalmology. The book is profusely illustrated with diagrams, charts and photographs. Written in English that is comprehendible and practiced by students in commonwealth countries.