Bardet−Biedl Syndrome
Dongyou Liu in 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).
Medical retina
Mostafa Khalil, Omar Kouli in The Duke Elder Exam of Ophthalmology, 2019
The retinal pigment epithelium (RPE) is composed of a single layer of cuboidal epithelial cells containing melanosomes and has many functions: Absorbs light and prevents the scattering of light within the eye.Replenishes the molecules needed for phototransduction.Contains a blood-retinal barrier, which provides a selectively permeable membrane to supply nutrients to the photoreceptors and maintain homeostasis. The blood-retinal barrier is maintained by the zonulae occludentes.Phagocytosis of photoreceptor outer segment membranes.Transport and storage of metabolites and vitamins.
SBA Answers and Explanations
Vivian A. Elwell, Jonathan M. Fishman, Rajat Chowdhury in SBAs for the MRCS Part A, 2018
The visual pathway may be summarized as follows: Photoreceptors (rods, cones) within the retina convert light energy into electrical impulses (phototransduction)This is transmitted to ganglion cells, directly via bipolar cells, or indirectly via horizontal and amacrine cellsGanglion cells are the output cells of the retina. Axons from ganglion cells converge at the optic disc (blind spot) and travel in the optic nerveIncomplete decussation occurs at the optic chiasm; those from the nasal half of each retina (corresponding to the temporal halves of the visual field) cross over (decussate), while those from the temporal halves of each retina stay on the same sideThe optic tracts synapse in the various layers of the lateral geniculate nucleus of the thalamus before being relayed to the primary visual cortex in the occipital lobe via the optic radiation
Are We Overlooking the Neurodegeneration in the Early Stage of Type 1 Diabetes Mellitus without Visual Impairment or Diabetic Retinopathy: Is It Probably Occurred before Retinal Vasculature Dysfunction?
Published in Current Eye Research, 2023
Yan Jia, Qiurong Lin, Ying Xiao, Xiaohong Zhou, Haidong Zou, Chenhao Yang
The pathogenesis of DR is complicated and multifactorial. Neurodegeneration and retinal vasculature dysfunction are two major pathophysiological features of DR.12,13 While the pathologic impact of diabetic is mainly observed on retinal vasculature, there is considerable evidence that the DR is the disease of the neurovascular unit and diabetes-induced changes in retinal neurons and glia, which precede the onset of clinically evident vascular injury.14–16 Retinal neurodegeneration may therefore represent an early event in the pathophysiology of DR and may also serve as the symbol of the onset of microvascular changes.17–19 Retinal dysfunction15,20–24 caused by reduced cone sensitivity, abnormal activation of the phototransduction cascade,25,26 selective loss of S cones,27 glial abnormalities, and thinning of the nerve fiber, the retinal ganglion cell (RGC) layer, and the inner plexiform layer in DR patients,28–30 has not received necessary attention from researchers. Highlighting the importance of further investigation, hyperglycemia-induced retinal neurodegeneration may precede the microvascular dysfunction and contribute to DR pathogenesis.31–34
Exploring the effects of large-area dorsal skin irradiation on locomotor activity and plasm melatonin level in C3H/He mice
Published in Chronobiology International, 2021
Xuewei Fan, Zeqing Chen, Wenqi Li, Haokuan Qin, Shijie Huang, Zhicheng Lu, Yinghua Li, Muqing Liu
Nonetheless, whether the skin has the ability to transmit this time information into body and even affect the central clock is still unclear. Some researchers have conducted relevant studies in human which are classified as extraocular phototransduction. Campbell and Murphy et al. found that intense light irradiation on popliteal region (behind the knee) could cause phase shift in core body temperature and dim light melatonin onset (DLMO), and even enhance rapid eye movement sleep (REM) (Campbell and Murphy 1998; Murphy and Campbell 2001). However, this finding was questioned by other researchers. Wright et al., in particular, obtained the opposite results in an almost identical experiments (Wright and Czeisler 2002). Recently, Wulff-Abramsson et al. observed that blindfolded people had different EEG signals when exposed to red, green or blue light (Wulff-Abramsson et al. 2019). This result suggested that light signals from skin appeared to be transmitted to the central nervous system and resolved by it.
Cystathionine β-synthase Deficiency Impairs Vision in the Fruit Fly, Drosophila melanogaster
Published in Current Eye Research, 2021
Marycruz Flores-Flores, Leonardo Moreno-García, Felipe Castro-Martínez, Marcos Nahmad
Once established, this Drosophila model of classical homocystinuria may be used to address several important questions about the disease. For instance, it could be used to identify genetic variations that might account for different visual phenotypes of the disease and its penetrance in different genetic backgrounds. The visual response of CBS-deficient flies can be further studied in different genetic backgrounds, for example using the Drosophila Genetic Reference Panel,38 a vast collection of isogenic fly lines that can be used in combination with genome-wide association studies39 to pinpoint genes that could enhance or reduce vision phenotypes in CBS-deficient flies. Another question that is beyond the scope of this work and is left for future investigations is the use of functional electrophysiology to relate how CBS-deficient flies affect the phototransduction cascade. Electroretinograms (ERGs) have been employed to link visual phenotypes to genotypes for more than 50 years40 and are widely used in Drosophila electrophysiology labs. How the eyes of CBS-deficient flies are affected at the functional level using ERGs is an immediate future direction of this study.