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Bardet−Biedl Syndrome
Published in Dongyou Liu, Handbook of Tumor Syndromes, 2020
Among the primary (cardinal) features of BBS, retinal degeneration includes rod-cone dystrophy, choroidal dystrophy, and global severe retinal dystrophy, of which rod-cone dystrophy (also referred to as retinitis pigmentosa due to defects in the transport of phototransduction proteins from the inner to the outer segments of photoreceptors causing rod and cone cell death) is most common, affecting 90%–100% of patients. Rod-cone dystrophy is a progressive retinal degeneration that usually manifests as night blindness by age 7 or 8, loss of color discrimination, and progressive tunnel vision (lose of peripheral vision) by the first decade of life, then loss of central vision and legal blindness by the second or third decade of life (Figure 25.1) [21–23]. Additional ophthalmologic features consist of nystagmus (rapid, involuntary eye movements), strabismus (lazy eye), high myopia, cataract (clouding of the lens), and glaucoma (damage to the optic nerve conducting signals to the brain).
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.
Lasers in Medicine: Healing with Light
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The anatomy of the eye is shown in Figure 3.30a. The white of the eye is called the sclera. Light enters the eye through the cornea and the pupil, the opening of the iris. It then passes through the lens and the vitreous humor, a jellylike substance that fills the eyeball, and falls upon the inner lining of the eyeball, called the retina. Both the cornea and the lens refract entering rays of light in such a way as to project tiny images of the outside world onto the retina, which plays a role analogous to the image sensor in a camera. The retina is a complex structure consisting of many specialized layers, including the pigment epithelium, which contains specialized cells for sensing light, and choroid, which contains blood vessels and dark blue pigments to absorb stray light. Some layers hold the rod and cone cells that actually sense light, some provide circulation and support. In the regions of the retina known as the fovea and the macula, or yellow spot, visual acuity is highest because of a high concentration of light-sensing cells. The optic disc, or blind spot, is where the optic nerve enters the retina. Preserving the functioning of these regions is of especial concern during laser surgery.
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).
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.
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.