Investigating The Molecular Mechanisms Responsible For Non Image Forming Visual Responses

Commonly known as Delayed Sleep Phase Disorder (DSPD) and other names, is a disorder in which the persons internal body clock is not in sync with the morning-rise evening-sleep pattern of the majority of people. Individuals with this disorder are not able to sleep and wake at the times that are regulated by normal work and school hours. They usually get enough sleep to keep them at a functional level through the day but not enough to be considered “well rested”. Polysomnography and actigraphy are tests commonly ordered for some sleep disorders to determine the illness. The cause of Delayed Sleep Phase can include a variety of reasons; puberty being one of the main causes, but some people are born with the disorder. The short term and long term effects of this illness is unfortunate for a person’s overall health. Overall cures to this disorder have not been found yet. Doctors have suggested sleeping pills to help or other alternatives. The disorder affects the timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily cycles.

Retinitis pigmentosa is a group of inheritable diseases that is characterized by gradual deterioration of the photoreceptors in the retina. The photoreceptor cells in the retina, rod cells, are light sensitive cells that are able to sense low levels of light. The frequency of retinitis pigmentosa is one in four thousand births (Deng et al., 2015; Fahim et al., 2012; Haddad et al., 2016; Shu et al., 2012) People affected by retinitis pigmentosa will typically exhibit symptoms of night-blindness first, and this will precede a loss in the patient’s visual acuity field that starts from the outer edge and gradually moves inward resulting in a much smaller visual field and loss of peripheral vision, also known as tunnel vision (Haddad et al., 2016).

To understand the diverse causes of RP, a basic understanding of visual perception is required. Phototransduction (conversion of light to electrical signals) occurs first, which is initiated by two types of photoreceptors: rods and cones. These two types vary in their function as rods are primarily responsible for night vision and lack sensitivity to color while cones function in color vision. Light contacts these photoreceptors, and isomerizes a retinaldehydechromophore (retinal) which is bound to varying types of opsin proteins corresponding in their reactivity to different wavelengths of light. Upon absorption of a photon of light, the chromophore 11-cis-retinal is isomerized to the all-trans confirmation, which subsequently causes a series of molecular interactions which ultimately result in the electrical response of the photoreceptors (Vugler 2010). As 11-cis-retinal is required to absorb photons of light, this compound must be regenerated, a function that is performed with the aid of nearby cells of the retinal pigment epithelium

The primate visual system is usually separated in two partially independent pathways; the dorsal pathway subserves mostly motion perception, while the ventral one subserves object feature recognition. The primary visual cortex (V1) receives most of its retinal input through the lateral geniculate nucleus (LGN). Anatomical and functional segregation of visual perception starts at the level of the retina, where parvocellular (P) ganglion cells have small receptive fields and have sustained colour-sensitive synaptic response to light, whereas magnocellular (M) ganglion cells have larger receptive fields and a faster adapting achromatic response to light [Livingston et al., 1992]. Both types of cells project to the layers 3-6 and 1-2 of the LGN, respectively, which in turn send most of their outputs to layers 4Cβ and 4Cα of V1, forming what is known as the P and M pathways [Refs].

Humans have a natural rhythm of 25 hours of sleep and wakefulness, in order to reset this the brain plays an important role with the suprachiasmatic nucleus which is a cluster of neurons in the medial hypothalamus of the brain. The SCN

McMahon , et al, 2014). Another factor that can play into S.A.D. is melatonin, which helps with sleep and wake cycles. Rosenthal, et al, notes how the pineal gland, the gland that produces melatonin, will react to dark surroundings with drowsiness that can lead people to being lethargic (as cited in Melrose, 2015). When melatonin increases and serotonin decreases, the offset of the proteins can cause circadian rhythms to be disrupted, which is the bodies “24 hour” clock. Researcher Melrose writes that “…circadian rhythms respond to the rhythmic light-dark changes that occur daily and throughout each of the seasons.” (2015). People with S.A.D. disorder normally find that their circadian rhythms are off beat and timed differently with day lengths, for example feeling tired in the middle of the day while being wide awake or feeling wide awake when it would normally be time to sleep.

According to O’Brien, Isayama, Richardson, & Berson (2002), the ganglion cells also consist of over a dozen different subtypes of cells and the functionality of these subtypes rely greatly on the individual responses that are stimulated by light entering into the retinal synaptic network. Early studies on ganglion cells in a cat’s retina showed that there were three physiological responses reported in the cat’s ganglion cells and that these cells had both a central and peripheral district within the retina. It was noted that both of these areas produce opposite effects upon activity of the ganglion cells (Enroth-Cugell, Goldstick, & Linsenmeier.

Chronotype (CT) is part of the circadian routine and it is defined as an individual’s inclination in rise and sleep timing (Horne & Ostberg, 1977). Chronotypes comprise three different groups; morning, intermediate, and evening group (Adal et al, 2012). Specifically, the early group rise and sleep early, while individuals who belong to the evening group rise and sleep later than the morning group, whereas the intermediate group does not follow a specific pattern (Adal et al, 2012). Interestingly, around 40% of the individuals belong to one of the two poles, morning or evening group (Adal et al,

Huntington’s disease (HD) is a neurodegenerative disease that affects roughly 10 individuals per 100,000 (Nopoulus, 2016). This disorder is normally associated with symptoms including motor impairment, namely slowed movements and random muscle contractions, as well as depression and cognitive dysfunction. However, another prominent symptom that has yet to be mentioned until recently is sleep disturbance and alteration of normal circadian rhythms. It is estimated that 60-90% of HD patients have sleep issues and that nearly 60% see those issues as being factors in their overall problems (Goodman et al., 2010). Despite the minimal volume of studies, the overwhelming proportion of HD patients who are afflicted with circadian dysfunction and

Duong, H., & Gest, T. (2013, June 6). Visual System Anatomy. Retrieved July 8, 2015,

This segment of the cell consists of of cell membrane in the form of disks that are packed closely together in order to ensure that multiple of these disks are inside. These disks contain the visual pigment called rhodopsin, a unique photosensitive molecule found only in rod cells that convert light into signal. Rhodopsin is made up of two proteins called opsin and retinal; when rhodopsin makes contact with light, it is broken down into these two proteins, and the light is then converted into a chemical signal that is sent to through the synaptic terminal towards the optic nerve. Due to rhodopsin breaking down easily and quickly under bright light, the overstimulation of rod cells is prevented and cone cells are used instead. In dim lighting, there is little rhodopsin that is being broken down, leading to a higher concentration of rod cells which allows better vision in the dark, which is the reason why rod cells are functional in

Aside from noticing night and day and clocks our body has its own system to tell us when to sleep and when to wake, our circadian rhythm. The human body naturally runs on a twenty five hour clock, so living on a twenty four hour schedule is often hard on the body because it loses an hour each day. On top of this natural loss most people do not get the right amount of sleep each night which can cause a whole host of problems. This is part of

Several researchers like (Burakova and Mazokhin-Porshnyakov, 1982; Mishra and Meyer-Rochow, 2008a) confirmed that the vesicles originate from inflation of the interretinular strands and are simply extensions of the cone cells. Shaw (1978) considered the presence of vesicles around the rhabdomere to be a typical feature of dark/light adaption. The location of the interretinular spaces suggests two possible functions. The first is to make physical contact with the rhabdomeres because both of them disappear in the nuclear region. The second, physiological function by increase sensitivity at the cost of resolution the presence of a palisade, which bodice the pigment granules away from the rhabdom. Finally, accordingly to (Horridge and Barnard, 1965) this IRSs have a light-guiding function apparently to protect the photoreceptors from damage by the allowing of stray light to entire the eyes.

As the eyes of other mammals, the ganglion cells of the human eye is not sensitive image forming on the retina receive the light signals

Sight a precious gift we cant take or granted, our eyes are the windows to the wonders of the woerld all we know and love experidne and discover, ponder and cherish. Lets peer into the workings of the eye. A uniae and self sustailning system. the reflecte light of the world. Light enters ino the crystal teansperency of the cornea, aqueous humor,lens, and vitreous humor, to projecr onto the photo re cemptors of the retina whos impoulses converge on the optic nerve, and then to the brain wto be transfigured into imagery and imbedded with meaning. continual adjustments to the puopil and lense regulate the entry and focusing of light in todays world the eyes surface is constantly challenged to protect itself and adjust to changing conditions. Ebeey blink helps our eyes antural devence system. The tear film, retains moister and retains visual acuity, tears contain natural disinfectants to kepe bacteria at bay alnd the tear system washes away impurities to maintain eye helth. The biology of our eyes inspires us to develop ways we can protect and maintain comfort for these remarkable structurews. For all the wonders our eyes provide throughout our lives we owe them our attentiona and ongoing care.