Distribution and Characteristics of Brain Dopamine
Nira Ben-Jonathan in 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.
Vision
Nicholas Green, Steven Gaydos, Hutchison Ewan, Edward Nicol in Handbook of Aviation and Space Medicine, 2019
Cone cells (three types): Respond to bright, photopic light.Predominate in fovea and parafoveal region; mediate fine detailed vision.Each type has different maximum wavelength sensitivities in line with short (S-blue), medium (M-green) and long (L-red) wavelength part of light spectrum.Perception of colour is complex; depends on overlapping factors such as hue colour brightness, contrast and degree of saturation.
Impact of Retinal Stimulation on Neuromodulation
Yu Chen, Babak Kateb in Neurophotonics and Brain Mapping, 2017
Another recent research has demonstrated that many subtypes of each kind of retinal cell exist. For instance, three types of cones, L, M, and S, respond to long, medium, and short wavelengths of light, respectively. Bipolar cells are separated into midget and diffuse general groupings, with many subtypes of those, but, functionally, they are considered to be activated by central or surrounding targets. There are ON cone bipolar cells (for each type of cone cell grouping) and OFF cone bipolar cells as well as ON and OFF rod bipolar cells. As for the inhibitory horizontal and amacrine cells, three types of horizontal cells have been identified in the human retina as of 1994 (Ahnelt and Kolb 1994), and more than 20 kinds of amacrine cells are separated into wide and narrow field classifications. The most commonly researched of these cells are the starburst amacrine and the AII cells. The AII cells link some rod and cone information before signals exit the eye, and the starburst cells are involved in directional sensitivity involved by optokinetic reflexes (Yoshida et al. 2001).
Electrophysiological Evaluation of Macular Photoreceptor Functions in Patients with Choroidal Neovascular Membranes
Published in Current Eye Research, 2023
Zeki Baysal, Hamidu Hamisi Gobeka
Full-field electroretinography (ERG) is a technique that objectively reflects a generalized cone system function from the whole retina under standard conditions with varying flash light intensities produced by a Ganzfeld (“full field”) stimulator.10 Around 6 million cone cells are found in the human retina. High spatial acuity is achieved due to the high density of cones (with low convergence) in the fovea. Furthermore, the presence of three cone types in the human retina that have different peak spectral sensitivities allows for a diverse range of color perceptions.11 The primary goal of intravitreal anti-VEGFs in nAMD is to treat CNVM in the macula. These agents may, however, have an impact on the function of macular cone cells. While animal and clinical studies have shown that IVR has no effect on retinal function as measured by ERGs,12,13 other studies have shown that repeated intravitreal anti-VEGFs may be toxic to the retina.5,7–9 In addition to systemic complications,14 intravitreal therapy has also been linked to severe ocular adverse effects.15 All these findings point to anti-VEGFs having both local and systemic toxicity, which warrants further investigation. However, the long-term effects of anti-VEGFs, particularly on retinal electrophysiological functions in nAMD, have received little attention.
Differential effect of a carotenoid-rich diet on retina function in non-diabetic and diabetic rats
Published in Nutritional Neuroscience, 2020
Kathleen J. McClinton, Michel Aliani, Sharee Kuny, Yves Sauvé, Miyoung Suh
Diabetic rats, after 9 weeks of STZ injection, showed both outer and inner retina functional deterioration with decreases in the amplitudes of rod-driven a-wave (photoreceptors), b-wave (inner retina, ON-bipolar cells and perhaps Müller cells), and rod-OPs (inner retina, amacrine cells), as well as increases in the implicit times of both a- and b-waves, and OPs. These functional changes in diabetes are in line with previous findings.19,20 Bui et al.21 also reported that ganglion cell dysfunction was most obvious in diabetes among other ERG components. Although our dark-adapted dimmest stimulus strength is higher than Bui’s (−2.4 log cd s/m2), only 25% of the diabetic rats, regardless of diet treatment, responded to this intensity in comparison to 100% of healthy control rats, confirming the abnormal ganglion cell function in diabetes. Less affected cone function may be due to less cone cell populations in rats; cones comprising only approximately 0.85% of total photoreceptors.22
Physical Activity Self-Efficacy in Older Adults with Vision Loss: A Grounded Theory Study
Published in Occupational Therapy In Health Care, 2023
Beth A. Barstow, Nataliya V. Ivankova, Laura K. Vogtle, Laura Dreer, Brian Geiger, Laurie A. Malone
In industrialized countries, the most prevalent cause of low vision is age-related macular degeneration (AMD) (NEI, 2020). The National Eye Institute (2020) defines age-related macular degeneration as a progressive chronic eye condition affecting the macular area of the retina. The macula, located in the central 20 degrees of the visual field, is composed primarily of cone cells responsible for providing information regarding the color, contrast and detail of objects and environments. Individuals with AMD have difficulty with tasks that require fine-detail vision such as reading, recognizing faces, and detecting low contrast drop-offs such as unmarked curbs (NEI, 2020). Additionally, individuals experience fluctuations in vision, macular scotomas, photophobia, and slow dark/light adaptation (NEI, 2020).
Related Knowledge Centers
- Color Vision
- Eye
- Fovea Centralis
- Optic Disc
- Photopic Vision
- Photoreceptor Cell
- Retina
- Rod Cell
- Visible Spectrum
- Scotopic Vision