Human Cone Light Sensitivity and Melatonin Rhythms Following 24-hour Continuous Illumination

Abstract

This study investigates the possibility of an endogenous circadian rhythm in retinal cone function in humans. A full-field cone electroretinogram (ERG) was performed every 2 h for 24 h under continuous rod-saturating ambient white light (53 ± 30 lux; pupils dilated) in nine healthy subjects. Distinct circadian variations were superimposed upon a gradual decrease in cone responsiveness to light, demonstrated most reliably in the implicit times of b-wave and oscillatory potentials, and to a lesser extent in amplitude and a-wave implicit times. After mathematical correction of the linear trend, the cone response was found to be greatest around 20:00 h and least around 06:00 h. The phase of the ERG circadian rhythm was not synchronized with the phase of the salivary melatonin rhythm measured the previous evening. Melatonin levels measured under constant light on the day of ERG assessments were suppressed by 53% on average compared to melatonin profiles obtained previously under near-total darkness in seven participants. The progressive decline in cone responsiveness to light over the 24 h may reflect an adaptation of the cone-driven retinal system to constant light, although the mechanism is unclear. The endogenous rhythm of cone responsiveness to light may be used as an additional index of central or retinal circadian clock time.

Circadian and Wake-Dependent Effects on the Pupil Light Reflex in Response to Narrow-Bandwidth Light Pulses

“…32 These and other studies lend support to the notion that there is a circadian modulation of the sensitivity of the nonvisual light photoreception system to light as already has been shown for the visual photoreceptive system. [33][34][35] Given that melanopsin is the primary circadian photoreceptor, we hypothesize that the intrinsic melanopsin-mediated pupil response may show a 24-hour variation that is influenced by the circadian clock and, therefore, will persist under constant dim lighting conditions. In our study, we addressed the question of whether the PLR varies with time of day.…”

Diurnal modulation of visual motion prediction

“…Moreover, those gene expressions fluctuate throughout the day. In physiological experiments, Danilenko et al (2011) recorded light adapted electroretinogram (ERG), and found that the b-component of ERG shows a marked circadian rhythm which peaks at 20:00 hours in human subjects. The b-component of ERG reflects intake into retinal Mü ller cells of potassium ions, which are pumped out from ON-type retinal bipolar cells.…”

The retinal clock in mammals: role in health and disease

“…Many of them have been shown to remain rhythmic in constant conditions and, hence, to be regulated by a circadian clock: this is the case for melatonin and DA synthesis, 75 phagocytosis of photoreceptor outer segments, 1 amplitude of the photopic ERG, 35,76 contrast sensitivity, 77 and rod-cone coupling. 78 Since the demonstration of the existence of an autonomous clock in the mammalian retina, 4 it has been essentially assumed that the rhythmic retinal functions are under the control of the retina clock seen as a whole.…”