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RetinoscopyRetinoscopy, also called the shadow test, is deservedly one of the most, popular methods of estimating eye refraction, though in some countries it is less used than other methods.

The chief advantage is that it is entirely objective, and is therefore very useful in the cases of young children, in those that are amblyopic, and in malingerers; besides, the method is very easily learnt and quickly carried out, saving much time in difficult cases of astigmatism.

Retinoscopy also enables us easily to detect small degrees of astigmatism which frequently exist, and, but for this method, would probably escape notice.

If light be reflected into the eye by means of a concave mirror, at a distance of a metre or so, an observer looking through the sight hole of the mirror will notice the ordinary red fundus reflex; on slightly rotating the mirror the illuminated area of the pupil may disappear (or, what may be more easily seen, the edge of the shadow bounding this illuminated area may appear), on the same side as the rotation or in the opposite direction, according to the refraction of the eye under observation; thus if the mirror be rotated to the right, and the edge of the shadow move across, the pupil also to the right, i.e. in the same direction as the rotation of the mirror, the case is one of myopia, whereas if the shadow had moved in the opposite direction to the mirror, the case would be one of hypermetropia.

This method of employing retinoscopy is so simple that a few practical trials will suffice to make it understood, although, af course, as in all other manipulations, some little practice is required in giving to the mirror the nercessary movements, and enabling one to appreciate what is seen.

Visit Eye disorders for more information about problems with the eye and measuring eye refraction.