Over the weekend of 21-23 February 1997, a small group gathered in Tallahassee, Florida, at the invitation of Ted Williams, to discuss "photo stasis and related topics." The majority of participants were former students and colleagues of Ted's, but an occasional outsider such as myself was generously included. The papers presented there are collected in this volume. The theory of photo stasis was first outlined in a landmark paper by John Penn and Ted, published in 1986 in Experimental Eye Research. They provided compelling data showing that, in the albino rat eye, levels of rhodopsin, outer-segment length, rhodopsin regeneration rate, and even, perhaps, rhodopsin packing density all depend on the levels of cyclic illumination (12 hours light, 12 hours dark) in which the animal was reared. So, for example, there is fourfold less rhodopsin in a retinal extract derived from an animal reared at 400 lux than in an extract from the retina of an animal reared at 3 lux. Animals reared at intermediate levels of light show intermediate amounts of rhodopsin that are correlated with illumination level. What these data immediately suggested is that the photoreceptor cell can adjust its photon-catching ability in response to the levels of light in which an animal is reared, and they also provided a compelling rationale for outer-segment turnover, a phenomenon discovered 20 years earlier by Richard Young but whose function has remained obscure.

Over the weekend of 21-23 February 1997, a small group gathered in Tallahassee, Florida, at the invitation of Ted Williams, to discuss "photo stasis and related topics." The majority of participants were former students and colleagues of Ted's, but an occasional outsider such as myself was generously included. The papers presented there are collected in this volume. The theory of photo stasis was first outlined in a landmark paper by John Penn and Ted, published in 1986 in Experimental Eye Research. They provided compelling data showing that, in the albino rat eye, levels of rhodopsin, outer-segment length, rhodopsin regeneration rate, and even, perhaps, rhodopsin packing density all depend on the levels of cyclic illumination (12 hours light, 12 hours dark) in which the animal was reared. So, for example, there is fourfold less rhodopsin in a retinal extract derived from an animal reared at 400 lux than in an extract from the retina of an animal reared at 3 lux. Animals reared at intermediate levels of light show intermediate amounts of rhodopsin that are correlated with illumination level. What these data immediately suggested is that the photoreceptor cell can adjust its photon-catching ability in response to the levels of light in which an animal is reared, and they also provided a compelling rationale for outer-segment turnover, a phenomenon discovered 20 years earlier by Richard Young but whose function has remained obscure.

" ... And the evening and the morning were the third day ... And God made two great lights; the greater light to rule the day and the lesser light to rule the night ... And the evening and the morning were the fourth day." The First Book of Moses, called Genesis (1: 13,16,19). There was daytime and nighttime before there was a sun or a moon. An interesting thought: How long were each of those first three days? Without a sun to reckon its length, a day could have been longer or shorter than 24 hours. Animals, says Genesis, appeared on the fifth day and by that time the sun and moon were illuminating the earth, presumably in cyclic fashion and with a period of 24 hours. A good thing, too, as readers of this monograph will as certain. The papers collected into this volume are written versions of 45 minute talks given at a symposium on "The Effects of Constant Light on Visual Processes," held at The Florida State University in Tallahassee on April 25-27, 1979. The conference was supported by the Psychobiology Program and handled, logistically, by the Center for Professional Development and Public Services. It was recognized that limitations on time and funds made prohibitive the invitation of others who may be doing interesting and related work. But, our earnest hope is that what is compiled here is a good blend of "true" light-damage and "relevant related" work."