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Diabetic Retinopathy
Published in Jahangir Moini, Matthew Adams, Anthony LoGalbo, Complications of Diabetes Mellitus, 2022
Jahangir Moini, Matthew Adams, Anthony LoGalbo
Fluorescein angiography shows a breakdown of the blood-retinal barrier, via leakage of the retinal capillaries. Even so, angiography is not the best test to evaluate whether macular edema is present or not. Leakage seen on an angiogram can occur without macular retinal thickening, so it is not diagnostic of macular edema.
Biochemical Markers in Ophthalmology
Published in Ching-Yu Cheng, Tien Yin Wong, Ophthalmic Epidemiology, 2022
Abdus Samad Ansari, Pirro G. Hysi
Non-exudative AMD remains a clinical challenge for clinicians to manage, given the difficulty in monitoring progression and lack of effective treatment. Proteomic studies have detected a moderate subclinical leakage of the blood–retinal barrier in this form of disease, suggesting that potentially harmful plasma components, including complement or iron, could enter the retina in AMD patients before advanced disease [161]. Therefore, therapies that stabilize the blood–retinal barrier might play a pivotal role in the future management of this disease.
Comparative Anatomy and Physiology of the Mammalian Eye
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
The RPE has several responsibilities in the maintenance of the health of the retina.133 It along with the retinal vasculature forms the blood-retinal barrier. It aids in the attachment of the retina by regulating the volume of fluid that enters the ocular ventricle and by a barb action of the elongated melanosomes in the villous processes.129,133The RPE has phagocytic properties, removing the shed outer segments of the photoreceptors. The bleached visual pigment is regenerated in the RPE and also the RPE is responsible for the transport and storage of vitamin A, an important component of rhodopsin, the rod visual pigment.129,133 In addition to vitamin A, the RPE is also responsible for the transport of other metabolites to the retina. The importance of the RPE is evident in the Royal College of Surgeons (RCS) rat in which the phagocytosis of shed outer segments is defective and results in the accumulation of the shed outer segments and subsequent photoreceptor degeneration.132
Retinal findings in glomerulonephritis
Published in Clinical and Experimental Optometry, 2022
Heather G Mack, Deborah J Colville, Phillip Harraka, Judith Anne Savige, Alessandro Invernizzi, Samantha Fraser-Bell
Whether complement dysfunction in retinal disease reflects local ocular complement abnormalities, abnormal complement formed in the liver and deposited in the eye, or a combination, is unclear. Large complement molecules are prevented from entering the retina by the blood-retina barriers. The inner blood-retina barrier consists of tight junctions between the non-fenestrated retinal capillary endothelial cells, surrounded by end-feet of Müller glial cells and astrocytes which secrete factors enhancing or disrupting the integrity of capillary endothelial cells. The outer blood-retina barrier is controlled by the RPE and is composed of tight junctions between the RPE cells. Bruch’s membrane, the semipermeable membrane between the RPE and the choriocapillaris, best thought of as a vessel wall between the RPE and choriocapillary basal laminae, provides a further barrier for the diffusion of molecules from the choroidal circulation into the retina.22
Diabetic eye: associated diseases, drugs in clinic, and role of self-assembled carriers in topical treatment
Published in Expert Opinion on Drug Delivery, 2021
Axel Kattar, Angel Concheiro, Carmen Alvarez-Lorenzo
Systemic administration of ocular drugs is compromised by the blood-retinal barrier. The inner limiting membrane of the retinal pigment epithelium prevents passage of high-molecular-weight molecules from blood to vitreous and vice versa [56]. Müller cells and astrocytes form tight junctions to regulate the passage of molecules between the outer choroid and the inner retina. Although the information on ocular bioavailability after drug systemic administration in humans is limited, some reports evidenced that for small drugs, such as ciprofloxacin, similar drug levels can be obtained in aqueous humor after topical instillation of the free drug or oral administration. The levels in vitreous humor are commonly higher after oral administration, but at expenses of exposing the whole organism to high drug dose [57]. Also, interestingly, the drug can be found in tear fluid after oral administration but not because of distribution through the eye, as reported for cyclosporine A [58]. The blood-retinal barrier efficiently prevents cyclosporine A diffusion from blood to the anterior segment, except during concomitance of inflammatory processes [59].
How to measure retinal microperfusion in patients with arterial hypertension
Published in Blood Pressure, 2021
Urszula Szulc, Edyta Dąbrowska, Janusz Pieczyński, Paweł Białkowski, Krzysztof Narkiewicz, Roland E. Schmieder, Joanna Harazny
The eye is supplied by two vascular systems, which differ in structure and function. Like in brain, retinal capillaries extending from the central retinal artery to the central retinal vein have endothelial tight junctions and form an inner blood–retina barrier, strongly resembling blood–brain barrier. The retinal capillaries are covered by astrocytes, in capillary bifurcations blood flow is regulated by pericytes [16]. In addition, the retinal vessels are not innervated by any efferent nerve fibres and fulfil primarily nutritional function in neural tissue. The retinal microperfusion is regulated by local and myogenic autoregulation. On the other hand, choroid vessels contain gap junctions, are innervated by fibres from the ciliary ganglion, and are separated from the retina by pigment epithelium – the external blood–retina barrier. Additionally, to the metabolic support of the pigment epithelium, photoreceptors, horizontal and bipolar cells, choriocapillaries play mostly thermoregulatory function, since the melanin in pigment epithelium absorbs light, what raises local temperature in the tissue.