The diurnal susceptibility of rat retinal photoreceptors to light-induced damage

Quantitative Relationship of the Scotopic and Photopic ERG to Photoreceptor Cell Loss in Light Damaged Rats

“…One difference between their study and ours is that we always began exposure after a long period of dark adaptation, while most of their exposures were given at the end of the normal light period. We have found, consistent with others (Duncan and O'Steen, 1985;White and Fisher, 1987;Organisciak et al, 1989), that darkness before bright light exposure greatly enhances susceptibility and, conversely, a short period of even dim light reduces susceptibility (unpublished observation). Thus, it is conceivable that prolonged darkness just before bright light exposure primes the retina for damage during the ®rst 24 hr of exposure, which is not greatly increased during the second 24 hr.…”

Protection of Photoreceptor Cells in Adult Rats from Light-induced Degeneration by Adaptation to Bright Cyclic Light

“…This indicates that the protective effect is dependent on the duration of the constant light challenge. The importance of circadian rhythms in the phenomenon of light damage has been demonstrated by Duncan and O'Steen (1985) and Organisciak et al (1998bOrganisciak et al ( , 2000, who presented evidence that the retina is the most sensitive to light damage in the dark half of the day/night cycle. It is proposed that with the increase in duration of bright constant light exposure for several days, the adaptation system established during the previous cyclic light (12 hr light/12 hr dark) period could be overwhelmed and lose the ability to compensate, and thus could fail to maintain the protective function.…”

Retinal light toxicity

“…The period of greatest potential damage correlate to the period of greatest outer segment phagocytosis. 128 While the previously mentioned studies do suggest that some relationship exists between photochemical damage to the retina and the settings of light exposure, it is also clear that adaptation mechanisms can have a vital function in reducing the susceptibility to light damage. Penn and Williams 129 described one of these adaptive effects, termed photostasis, in which the concentration of rhodopsin is regulated so that the relative absorption of photons remains steady and independent of the intensity of environmental light.…”