The examination and correction of errors of ocular refraction may be called an art. Preparatory scientific study is, of course, necessary; but without the proper mental attitude—an absolute belief in the importance of correcting small refractive errors, the best work is not possible. Long practice, infinite care, and attention to finer details are imperative requisites. It is an established fact that many of the worst sufferers of ametropic eyestrain are the subjects of small optical errors. Astigmatism is the important defect, and on its proper diagnosis and treatment rests most of the ophthalmologist's success.
A slight fault in the correction of refractive errors aggravates rather than relieves the accompanying asthenopic symptoms. By applying sufficient optical aid to allow the ciliary muscle to compensate perfectly for the uncorrected refractive defect, continuous rather than intermittent ametropic eyestrain is established. In such cases the sufferers, apparently visually competent and resting assured that their