Retinoscopic and neurophysiological refractometry in rana temporaria.

If frogs are measured by objective refractometry one finds a hyperopia of 6 D to 9 D. Therefore we investigated the neurophysiological state of refraction of the immobilized rana temporaria using the technique of extracellular recording. In the superficial neuropil the neural activity of 32 recorded neurons showed no dependence on the state of refraction which was changed between−10 D and +20 D. In the deep part of the tectum opticum, below the stratum album centrale, we could observe 11 cells with a strong dependence upon the state of refraction. The neural activity was maximum at +3 D, that is the optical distance of the test screen. This finding means that our investigated frogs were physiologically emmetropic. [ABSTRACT FROM AUTHOR]