The Role of Vitamin A in Retinal Diseases

Abstract

Vitamin A is an essential fat-soluble vitamin that occurs in various chemical forms. It is essential for several physiological processes. Either hyper- or hypovitaminosis can be harmful. One of the most important vitamin A functions is its involvement in visual phototransduction, where it serves as the crucial part of photopigment, the first molecule in the process of transforming photons of light into electrical signals. In this process, large quantities of vitamin A in the form of 11-cis-retinal are being isomerized to all-trans-retinal and then quickly recycled back to 11-cis-retinal. Complex machinery of transporters and enzymes is involved in this process (i.e., the visual cycle). Any fault in the machinery may not only reduce the efficiency of visual detection but also cause the accumulation of toxic chemicals in the retina. This review provides a comprehensive overview of diseases that are directly or indirectly connected with vitamin A pathways in the retina. It includes the pathophysiological background and clinical presentation of each disease and summarizes the already existing therapeutic and prospective interventions.

Posterior placoid-like maculopathy and macular hole associated with vitamin A deficiency

“…Retinal findings in VAD are typically described as multiple round yellow-white lesions in the macula and midperiphery captured on OCT as drusenoid subretinal deposits. 11 , 12 , 13 These yellow deposits are theorized to represent accumulating shed photoreceptors from a disrupted retinoid cycle layering between the RPE and ellipsoid band, causing blocked hypo-autofluorescence and appearing as hyperreflective deposits on OCT. 12 , 14 In reports describing VAD retinopathy, treatment with vitamin A supplementation usually improved retinal function, resolved symptoms, and cleared the yellow deposits. 15 , 16 In our case, the patient experienced profound subjective improvements in vision within weeks of initiating vitamin A replacement therapy, with notable anatomic improvements as well.…”

Vitamin K and the Visual System: A Narrative Review

“…It is well established that the fat-soluble vitamins (FSV) A, D, and E play essential roles, and in some cases can have toxic effects, in the eye and visual system [227][228][229]. Vitamin A in the form of 11-cis-retinal is indeed the singular light sensitive molecule setting in motion the visual cycle resulting in the transduction of photons into nervous impulses [228], and its deficiency has been heralded by night blindness and xerophthalmia for millennia-the direct result of which lead to its discovery as the first FSV [125]. Vitamins D [227] and E [229], likewise have been shown to have pleotropic benefits as well as rare toxicity for the EVS, with toxic levels of A, D, and E, unlike VK, able to accumulate within the body [230].…”

ACE-Vitamin Index and Risk of Glaucoma: The SUN Project

“…Vitamin A can be obtained as preformed vitamin A (such as retinol) and provitamin A (such as beta-carotene). It is a fat-soluble vitamin that can be stored in the liver, and it is therefore unnecessary to take it daily [ 18 ]. The Recommended Dietary Allowance for adults is 900 μg daily for men and 700 μg for women [ 19 ], and our participants showed a median vitamin A consumption of 2530 μg/day.…”

“…Vitamin A is related to white blood cell function, bone remodeling and endothelial cell maintenance, and it has a favorable immune-modulating effect [ 20 , 21 ], but one of its most important functions is its role in visual phototransduction, facilitating the process of the transformation of light photons into electrical signals. It also serves to protect the conjunctiva and to alleviate symptoms of dry eye [ 18 ]. Several studies have previously analyzed the relationship between this vitamin and the incidence of glaucoma, most of which did not find any significant relationship [ 22 ].…”