ABSTRACT
Retinal ganglion cells (RGCs) are final output neurons from the retina to the brain, which can transmit light signals and participate in image-forming vision (IFV) (image formation) and non-image-forming vision (NIFV) (non-image formation). Visual processing system not only transmits visual information of images, but also influences human physiological activities and behaviors by incoming optical signals, which is called NIFV.NIFV relies less on signals generated by conventional photoreceptor cells, but a special class of intrinsically photosensitive retinal ganglion cells (ipRGCs). ipRGCs are a subset of retinal ganglion cells that express melanopsin.The axons of the ipRGCs project to unique targets and modulate a broad range of NIFV behaviors, from basic physiological regulation (such as heart rate and pupil size) to more complex behavioral regulation (such as circadian rhythm) and even higher-level cognitive processes (such as anxiety and other emotions). NIFV circuit is an important response to light, and ipRGCs plays a vital role in NIFV circuit.This article reviewed the regulation of NIFV circuit in physiological activities and behaviors, summarized the relationship between the projections of ipRGCs to the NIFV function, and provided ophthalmologists with more knowledge of visual system.
ABSTRACT
Non-image forming functions of eyes include the regulation of biological circadian rhythm and biological magnetoreception.Biological magnetoreception means that various organisms including human obtain the direction and position information through the geomagnetic field.Creatures with retina realize magnetoreception regarding retinal cryptochrome as magnetoreceptor.Hypotheses of magnetoreception contain the radical-pair theory and the biological compass theory.The two theories both reckon retinal elements as possible receptor protein of magnetoreception, and eyes as receptor organ.The radical-pair theory suggests that change of radical spin influences the structure of retinal cryptochrome, leading to different downstream chemical reaction products, which makes the variable magnetic field information perceivable.And the biological compass theory proposes a rod-like complex composed of polymerized cryptochromes and magnetoreceptor proteins, which can point to different directions due to light and magnetic signals.These changes in retina transmit geomagnetic field signal to the brain, and then sense of direction is formed.Researching biological magnetoreception promotes a novel perspective in the diagnosis and treatment of eye and brain diseases, and brings innovation in magnetic material field.In this article, non-image forming functions of eyes, hypotheses of magnetoreception and possible mechanism of non-image forming functions of eyes in magnetoreception were reviewed.
ABSTRACT
Mammalian eyes mediate both image-forming and non-image-forming visual functions. Non-image-forming vision provides a measure of the ambient light for the purposes of synchronization of circadian clocks to light/dark cycles and regulation of pupil size,pineal melatonin production and other functions. Traditionally,people used to believe that the classical photoreceptors (rods and cones) regulate both image-forming and non-image-forming visual pathways. However,a small subset of retinal ganglion cells called intrinsically photosensitive RGCs ( ipRGCs) has been identified to be a third type of mammalian photoreceptor and determined to be photosensitive, recently. The discovery of ipRGCs has allowed for rapid progress in the past decade toward understanding the non-image-forming visual system,especially about how the circadian clock complete the synchronization with the light/dark cycle. The anatomical and developmental characteristics of ipRGCs, as well as its biological functions and regulation were reviewed in this paper.