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PubMed1962

Direct action of light in naturally pigmented muscle fibers. I. Action spectrum for contraction in eel iris sphincter.

Contraction due to light in excised eel irises appears to follow a simple first order law. The action spectrum for contraction has a maximum which agrees with the eel rhodopsin absorption maximum. Inasmuch as rhodopsin is the rod pigment-opsin complex and the iris sphincter pupillae evolves from the pigment epithelium of the retina in the region of the iris, the muscle pigment might be the same as the visual pigment. In the human eye the contraction of the iris sphincter is activated only by light incident on the retina and the pupil diameter varies inversely with the square root of the light intensity. The inverse first power relation observed in the present experiments suggests a more primitive origin for the light reaction in eel irises. Relaxation is a much slower process and can be approximated as the sum of two first order processes.

Adaptation, Ocular↗
PubMed1963

THE DEPENDENCE OF THE PHOTOPUPIL RESPONSE ON FLASH DURATION AND INTENSITY.

The changes in pupil size were recorded by infrared pupillographic methods in response to light flashes of different durations and intensities for a 13 degree 34 minute centrally fixated circular field. For such stimuli, the threshold intensities for (rod) vision and for the pupil response were found to be about the same. The response amplitudes were related to the logarithm of the flash energy, the reciprocity law remaining valid up to about one-half second. The curve relating flash energy and pupil response was clearly divisible into two parts commensurate with the duplex character of the human retina. A similar dichotomy appears in curves relating response amplitude to response latency. Since the pupil response is determined by total flash energy, intense long flashes produce larger pupil responses than shorter (and perceptually brighter) ones of the same intensity.

Adaptation, Ocular↗
PubMed1964

PROBABILITY OF OCCURRENCE OF DISCRETE POTENTIAL WAVES IN THE EYE OF LIMULUS.

Discrete potential waves can be recorded from cells in the eye of Limulus both in darkness and in dim illumination. With constant illumination the frequency of these waves is linearly related to light intensity and the distribution of intervals between waves follows an exponential function. The latency of waves evoked by short flashes of light is usually long and variable and the number of waves evoked by a flash varies randomly, obeying approximately a Poisson distribution. The results of experiments with flashes of light have been compared with the predictions derived from the hypotheses that one, two, or three quanta of light are required for production of one wave. The agreement of the data with the theory can be considered acceptable for the "one quantum" hypothesis, is less satisfactory for the "two quanta" hypothesis, and is very poor for the "three quanta" hypothesis.

Adaptation, Ocular↗
PubMed1965

VISUAL ADAPTATION.

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Adaptation, Ocular↗