Optical measurement of the refraction of the eyes in frogs ( Rana pipiens).

It has been assumed until recently that frogs were hyperopic as observed by retinoscopy, which is the universal method of objective refraction. However this method is believed to be erroneous because light is reflected by a layer other than that of the receptors. Using a refractometer in which light is focused in the eye and viewed ophthalmoscopically, the eyes of the frog are found to be emmetropic. It is assumed that these data are valid because of the underlying principle of this instrument, and because this result is in agreement with recent electrophysiological measurements. [ABSTRACT FROM AUTHOR]