China
Africa
Explore chapters and articles related to this topic
Medical and Mathematical Background
Published in Arwa Ahmed Gasm Elseid, Alnazier Osman Mohammed Hamza, Computer-Aided Glaucoma Diagnosis System, 2020
Arwa Ahmed Gasm Elseid, Alnazier Osman Mohammed Hamza
The retina is a multi-layered sensory tissue that lies at the back of the eye, and contains millions of photoreceptors that capture light rays and convert them into electrical impulses that will in turn convert them into images in the brain. The main photoreceptors in the retina are rods and cones. Rod cells are very sensitive to changes in contrast, even at low light levels, hence they are able to detect movement, but they are imprecise and insensitive to color located in the periphery of the retina and are used for scotopic vision (night vision). Cones are high precision cells capable of detecting the colors that are concentrated in the macula, the area responsible for photopic vision (day vision). The very central portion of the macula is called the fovea, which is where the human eye is able to best distinguish visual details. The loss of peripheral vision may cause damage to the macula and can result in the loss of central vision.
Distribution and Characteristics of Brain Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
The retina of the eye has two types of DA-producing cells: amacrine cells (ACs), which lack axons (anaxonic), and inteplexiform cells (IPC), which have multiple processes [14,15]. The AC are a diverse class of intrinsic interneurons of the inner retina (Figure 3.6). They receive synaptic input from the bipolar cells as well as from other amacrines and in turn provide input to the ganglion cells and feedback information to the bipolar cells. These cells release DA into the extracellular milieu and are especially active during the daylight hours, becoming silent at night. The retinal DA enhances the activity of cone cells (which are responsible for color vision and spatial acuity) while suppressing rod cells (which are responsible for vision at low light levels). Consequently, DA increases retinal sensitivity to color and contrast during bright light conditions but at the cost of reduced sensitivity when the light is dim. The circadian rhythm of retinal DA levels is independent of input from the suprachiasmatic nucleus, the master circadian pacemaker, and depends on the actions of locally produced melatonin and GABA. Patients with Parkinson’s disease have reduced retinal DA levels and suffer from a number of visual dysfunctions. Impaired color and contrast discrimination has been considered as preclinical signs of Parkinson’s disease.
The vitamins
Published in Geoffrey P. Webb, Nutrition, 2019
Rhodopsin is the light-sensitive pigment in the rod cells of the retina. It is comprised of 11-cis retinal (the chromophore) and a protein called opsin. Within the eye, all trans retinol (vitamin A) is converted by enzymes to 11-cis retinal and this binds spontaneously with opsin to form rhodopsin. Light induces isomerisation of the 11-cis retinal in rhodopsin to all trans retinal, and this causes the opsin and retinal to dissociate and the pigment to become bleached. It is this light-induced cis-to-trans isomerisation that generates the nervous impulses that we perceive as vision. Enzymes in the eye then regenerate 11-cis retinal and thus rhodopsin (summarised in Figure 15.2).
Intravitreally Injected Methylene Blue Protects Retina against Acute Ocular Hypertension in Rats
Published in Current Eye Research, 2022
Zhiqiang Ye, Xiaoli Li, Dongliang Zheng, Shuaili Pei, Pei Cheng, Lishu Zhang, Lin Zhu
Flash ERG is a powerful physiological examination for the investigation of retinal function, which shows the retinal cells state. Many electrophysiological parameters were very relevant to the retinal tissue integrity, as well as the resident cells state.36 In the current study, the ERG response amplitudes of b-waves were statistically recovered in MB-treated eyes compared with NS-treated eyes after AOH injury, suggesting that MB could partially reduce retinal functional changes. Moreover, in the AOH + MB group, b-wave amplitudes seem to be better preserved in the scotopic ERG compared with the photopic ERG, with no significant statistical difference at 14 and 28 days after AOH in photopic ERG (AOH + MB vs. AOH + NS). MB seemed to produce a weaker effect on photopic ERG than scotopic ERG, indicating that bipolar cells and its connected rod cells may be the main target for MB in the retina. Considering the greater number of rod cells in the normal retina than cone cells, we need further investigation to prove our proposed theory. In addition, Flash ERG mainly reflects the activity of retinal cells apart from the RGCs; to better determine the neuroprotective effect of MB on RGCs, pattern ERG has been considered in our future studies.
An optometrist’s guide to the top candidate inherited retinal diseases for gene therapy
Published in Clinical and Experimental Optometry, 2021
Fleur O’Hare, Thomas L Edwards, Monica L Hu, Doron G Hickey, Alexis C Zhang, Jiang-Hui Wang, Zhengyang Liu, Lauren N Ayton
Retinitis pigmentosa can be characterised by photoreceptor dysfunction that is either primary (a gene critical for rod or cone cell function is mutated e.g. RHO in rod cells), or secondary (the mutation affects the function of a non-photoreceptor cell e.g. RPE65 for the retinal pigment epithelium),24 which subsequently affects rod and cone function, leading to photoreceptor degeneration.25 Retinitis pigmentosa is further classified as ‘non-syndromic’ if the condition is isolated, or ‘syndromic’ if associated with systemic anomalies such as Usher Syndrome, a leading cause of auditory and visual impairment.26,27 Additionally, other clinical categories may also be applied that relate to the temporal pattern of disease (i.e. rod-cone versus cone-rod versus cone, and stationary versus progressive).
Exome sequencing identified five novel USH2A variants in Korean patients with retinitis pigmentosa
Published in Ophthalmic Genetics, 2023
SeungHee Jung, Young Chan Park, DongHee Lee, SiYeon Kim, Sang-Mo Kim, YoungJin Kim, DongHyun Lee, JaeJoung Hyun, InSong Koh, Jong-Young Lee
Retinitis pigmentosa (RP; OMIM #26800) is the most common inherited retinal degeneration, and is characterized by the progressive degeneration of photoreceptors. The prevalence of non-syndromic RP is around 1 in 4,000 (1). Most patients with RP experience night blindness in the early stages of the disease; the gradual loss of rod cells leads to loss of peripheral vision, and in critical cases, severe visual impairment can occur owing to loss of cone cells (2). The manifestations of RP are usually confined to the eyes. However, some patients with RP have syndromes affecting non-ocular organs. One of the representative syndromes of RP is the Usher syndrome, which is characterized by progressive visual loss accompanied by deafness.