A fundamental step-transition in retinal function at low light intensities.

There appears to be a fundamental step-transition in retinal function at low light intensities, close to the scotopic-mesopic transition. This step-transition is observed for elements of the retinal dark-light switch, which has been described in the chicken retina. Over the same range of light intensities, there is a step-transition in photoreceptor retinomotor movements and in the coupling of horizontal and All amacrine cells, which suggests a switch in retinal circuitry from rod-processing to cone-processing regimes. A similar step-transition in pineal function suggests that the retinal step-transition signals to the central circadian systems. Finally, this step-transition may also inhibit eye growth, and thus be responsible for the reported diurnal rhythm in eye growth. Disturbances to this step-transition may be the initial cause of disordered eye growth in the form-deprivation myopia paradigm.