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Ophthalmologic Side Effects
Published in Ayse Serap Karadag, Berna Aksoy, Lawrence Charles Parish, Retinoids in Dermatology, 2019
Some patients may experience decreased dark adaptation and night blindness during retinoid treatment, but this is reversible. Isotretinoin can cause reversible abnormalities in the function of rod cells in rats that can be documented with electroretinography (27). Administration of high dose isotretinoin to rats (40 mg/kg) slows recovery of rod signaling after bleaching by slowing down the regeneration of rhodopsin (a complex protein sensitive to light that contains another vitamin A derivative, 11-cis retinal, as cofactor) in the visual cycle; however, rod functions become normal after dark adaptation, when enough time is allowed for the delayed recovery of rhodopsin and no histological damage occurs at the retinal tissue (28). Decreased color vision may occur during isotretinoin treatment but this is also reversible (4). The incidence of this adverse effect is very low and could not be repeated in some studies (27,29). Both isotretinoin and acitretin treatments are also associated with a reduction in contrast sensitivity (5,30). There is no detailed study on the influence of acitretin, bexarotene, and alitretinoin on dark adaptation; however, package inserts of acitretin and alitretinoin also list night blindness among the adverse events (22,25).
Impact of Retinal Stimulation on Neuromodulation
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
The most familiar of the retina’s ten layers is the one with photoreceptors, split into the outer and inner segments of rods and cones. Photoreceptors need nourishment from another retinal layer, the retinal pigment epithelium (RPE). The constant interaction between the RPE and the rod photoreceptors is termed the visual cycle, triggered by lighting changes. Cones have a chemical interchange with Mueller cells. The external limiting membrane (or outer limiting membrane) separates the cell bodies of the photoreceptors from their outer and inner segments. The line of cell bodies is termed the outer nuclear layer of the retina. Oftentimes, a photoreceptor integrity line is evaluated on retinal imaging, but it is not a retinal layer. It simply represents the junction between the outer and inner segments of the photoreceptors, and its assessment is useful for determining the progress of various diseases.
Vitamin A
Published in Judy A. Driskell, Ira Wolinsky, Sports Nutrition, 2005
Maria Stacewicz-Sapuntzakis, Gayatri Borthakur
Vitamin A constitutes a vital part of our visual system.2 Photoreceptors of the retina in the eye (rods) contain rhodopsin, a photo-sensitive pigment composed of 11-cis-retinal and a protein, opsin. Visual impulse is produced when 11-cis-retinal absorbs a photon, changes to all-trans-retinal, and disengages from opsin. For continuous vision, rhodopsin must be regenerated by isomerization of all-trans-retinol to 11-cis-retinol and the oxidation of the latter to 11-cis-retinal. These reactions proceed in retinal pigment epithelium (RPE), which contains a local pool of retinyl esters and the specific enzymes. The visual cycle continues because 11-cis-retinal is transported back to the rods to combine with opsin. The first symptom of vitamin A deficiency is an impaired dark adaptation, which develops into night blindness.
Cross-sectional assessment of the ellipsoid zone and the retinal pigment epithelium-Bruch membrane complex after systemic isotretinotin use
Published in Cutaneous and Ocular Toxicology, 2022
İrem Genç Işık, Mehmed Uğur Işık
Another analogue of vitamin A, 11-cis-retinoic acid, plays a fundamental role in visual physiology via its turnover between retina pigment epithelium (RPE) and photoreceptors. The visual cycle is initiated by a photon that reacts with rhodopsin which contains 11-cis-retinal structurally. 11-cis-retinal released from opsin with the reaction initiated by light, turns into all-trans-retinal and is reduced to all-trans retinol. All-trans-retinol is translocated from photoreceptors to RPE. In RPE, all-trans-retinol is esterified to form all-trans-retinyl esters and then isomerized to 11-cis-retinol. 11-cis-retinol is reduced to 11-cis-retinal and transported to photoreceptors5. In a study conducted on rats, after administration of isotretinoin, 11-cis retinal levels reduced and retinyl-esters increased in eye tissue extracts6. The same study showed that isotretinoin slowed the rod and cone recovery time6.
Gene therapy for Leber congenital amaurosis
Published in Expert Review of Ophthalmology, 2018
Neruban Kumaran, Alexander J. Smith, Michel Michaelides, Robin Ali, James Bainbridge
RDH12 encodes a broad specificity aldehyde reductase localized in photoreceptor inner segments. The protein is not essential in the visual cycle, but is believed to protect against toxic accumulation of all-trans-retinal under persistent illumination [41]. Disease-causing sequence variants in RDH12 account for approximately 10% of LCA/EOSRD [19,42]. AAV2/8-vector-mediated RDH12 gene replacement therapy in Rdh12 knockout mice indicates the potential for benefit in affected humans [43].
Emerging biological therapies for the treatment of age-related macular degeneration
Published in Expert Opinion on Emerging Drugs, 2021
Masumi G. Asahi, Jaycob Avaylon, Josh Wallsh, Ron P. Gallemore
Fenretinide, a synthetic retinoid derivative, targets the visual cycle indirectly by preventing retinol (vitamin A) delivery to the RPE, showed a dose dependent association with reduced GA lesion growth rate[24]. Other studies have also supported the harmful effects of vitamin A for AMD and serves as another reason for exclusion of vitamin A from various AREDS2 formulations [25,26].