Visual impairmentVisual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as corrective eyewear, assistive devices, and medical treatment– visual impairment may cause the individual difficulties with normal daily tasks including reading and walking. Low vision is a functional definition of visual impairment that is chronic, uncorrectable with treatment or conventional corrective lenses, and impacts daily living.
RetinaThe retina (from rete "net"; : retinae or retinas) is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or in a camera.
Retinal detachmentRetinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a surgical emergency. The retina is a thin layer of light-sensitive tissue on the back wall of the eye. The optical system of the eye focuses light on the retina much like light is focused on the film in a camera.
Retinal ganglion cellA retinal ganglion cell (RGC) is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells. Retina amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and making it so that ganglion cells can observe a small dot moving a small distance.
Retinitis pigmentosaRetinitis pigmentosa (RP) is a genetic disorder of the eyes that causes loss of vision. Symptoms include trouble seeing at night and decreasing peripheral vision (side and upper or lower visual field). As peripheral vision worsens, people may experience "tunnel vision". Complete blindness is uncommon. Onset of symptoms is generally gradual and often begins in childhood. Retinitis pigmentosa is generally inherited from one or both parents. It is caused by genetic variants in nearly 100 genes.
Retinal pigment epitheliumThe pigmented layer of retina or retinal pigment epithelium (RPE) is the pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells, and is firmly attached to the underlying choroid and overlying retinal visual cells. The RPE was known in the 18th and 19th centuries as the pigmentum nigrum, referring to the observation that the RPE is dark (black in many animals, brown in humans); and as the tapetum nigrum, referring to the observation that in animals with a tapetum lucidum, in the region of the tapetum lucidum the RPE is not pigmented.
Photoreceptor cellA photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential. There are currently three known types of photoreceptor cells in mammalian eyes: rods, cones, and intrinsically photosensitive retinal ganglion cells.
Visual fieldThe visual field is "that portion of space in which objects are visible at the same moment during steady fixation of the gaze in one direction"; in ophthalmology and neurology the emphasis is on the structure inside the visual field and it is then considered “the field of functional capacity obtained and recorded by means of perimetry”. However, the visual field can also be understood as a predominantly perceptual concept and its definition then becomes that of the "spatial array of visual sensations available to observation in introspectionist psychological experiments" (for example in van Doorn et al.
Rod cellRod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 92 million rod cells (vs ~6 million cones) in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision.
Intrinsically photosensitive retinal ganglion cellIntrinsically photosensitive retinal ganglion cells (ipRGCs), also called photosensitive retinal ganglion cells (pRGC), or melanopsin-containing retinal ganglion cells (mRGCs), are a type of neuron in the retina of the mammalian eye. The presence of (something like) ipRGCs was first suspected in 1927 when rodless, coneless mice still responded to a light stimulus through pupil constriction, This implied that rods and cones are not the only light-sensitive neurons in the retina.
