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Iron, Oxygen Stress, and The Preterm Infant
Published in Bo Lönnerdal, Iron Metabolism in Infants, 2020
Singlet oxygen is formed if the spin of one of the unpaired electrons of oxygen is changed in a way that permits oxygen to react with a nonradical (Table 1). Singlet oxygen is, therefore, a very reactive species. Formation of singlet oxygen has been recognized if porphyrins are exposed to visible light12 and in the lens and the retina of the mammalian eye.13
Retinal stem cell research
Published in A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha, Vitreoretinal Surgical Techniques, 2019
Henry Klassen, Michael J Young, Robert Ritch, Julia E Richards, Teresa Borrάs, Leonard A Levin
In one approach, a brain-derived cell could be genetically modified to induce transdifferentiation along a retinal lineage. Alternatively, a less differentiated cell type such as an ES cell could be induced to differentiate toward a retinal fate. We and several other groups have chosen a third strategy, namely, the isolation of progenitor cells from the neural retina of the developing mammalian eye. Upon transplantation to the retina of adult mammals with retinal disease, murine RPCs possess both the integrative plasticity characteristic of CNS stem cells and the ability to differentiate into retina-specific neurons such as photoreceptors (Fig. 68.2). Further studies of RPC grafts are needed to set the stage for the development of clinical strategies aimed at restoring vision to the blinded eye.
The Internal Milieu Brain and Body
Published in Rolland S. Parker, Concussive Brain Trauma, 2016
Entrainment: This is the process by which an endogenous rhythm is regulated by a zeitgeber (an external cue, e.g., the light-dark cycle) to synchronize endogenous rhythms. Rhythms are normally entrained to a light-dark cycle with a period of 24 h and a stable phase relationship to the timing of the solar cycle. It is mediated by the photopigment melanopsin, which is located in retinal ganglion cells that project through the RHT to the SCN and the intrageniculate leaflet (IGL) independently of the familiar retinal circuits to the geniculate colliculus and accessory optic systems. The body’s natural rhythm is now estimated at 24.2 h (Czeisler et al., 2005), which is periodically reset by light stimuli. For the body clock to be useful, it should be adjusted to the actual solar day. Rhythmic cues in the environment are known as zeitgebers (time-givers) whose effect on the body clock depends on its time of presentation (a phase advance, delay, or no phase shift). The primary zeitgebers are the light-dark cycle and rhythmic secretion of the pineal hormone melatonin, during nocturnal sleep in healthy people. Circadian rhythms persist in the absence of a light-dark cycle, with a free-running period that is slightly more than 24 h. The mammalian eye appears to have a circadian pacemaker maintaining the rhythm of visual sensitivity.
Nanotechnology: revolutionizing the delivery of drugs to treat age-related macular degeneration
Published in Expert Opinion on Drug Delivery, 2021
The corneal epithelium is the first barrier of entry for xenobiotics, but the eye’s rich blood supply poses a much bigger challenge in drug transport to the posterior region. The mammalian eye is innervated by a blood supply to provide for oxygen transport and pathogen defense. The anterior region of the eye has a blood ocular barrier composed of endothelial cells of the uvea and is composed of the BRB, posteriorly Both these barriers regulate the passage of pathogens as well as foreign substances which include drugs. Further, the retina is a highly vascular tissue that also contains a dual blood supply source. The inner and central portion of the retina is supplied by retinal blood vessels and outside choroidal circulation. Whether the drug is administered anteriorly or posteriorly for the treatment of retinal eye disease, it must cross tight retinal junctions which are reinforced by a powerful retinal blood barrier, called the RPE. Efflux transporters (P-glycoprotein, multi-drug resistance protein) may further reduce the distribution of the drug in ocular tissues [40–43].
Fine structure of the human retina defined by confocal microscopic immunohistochemistry
Published in British Journal of Biomedical Science, 2021
The advanced understanding of the mammalian retina is crucial in the investigation and treatment of ophthalmological disease, and study of the mammalian eye has provided insight [1–3]. Although these studies are informative, human tissues are becoming widely available, providing the opportunity to study the morphology and function of the retina in our own species, which is commonly characterized using cell markers that label specific neurons or glia [4]. Despite similarities in retinal anatomy between humans and other animal species, cell marker immunoreactivity varies between species. For example, antibodies to parvalbumin have been reported to stain AII amacrine cells in both the rat and rabbit retina [5], but in humans, strong immunoreactivity was observed in horizontal cells [6], and calretinin is a suitable marker for AII amacrine cells in the human retina [7]. These data call for a comprehensive study into their potential value in the study of the human eye.
A Comparison of Applanation and Rebound Tonometers in Young Chicks
Published in Current Eye Research, 2021
Lisa A. Ostrin, Christine F. Wildsoet
That age-related increases in eye length may contribute to the observed over-estimation of IOPs taken with the TonoLab is an alternative possibility that is indirectly supported by a study in humans. Specifically, in a comparison of IOPs recorded using rebound compared to Goldmann applanation tonometry,56 rebound tonometry readings were found to be higher than applanation tonometry readings, with myopic eyes showing the highest overestimation. The eyes of young chicks enlarge rapidly over the first few months of life, from approximately 8.5 mm at hatch to 11 mm in length by 6 weeks of age.57 There are also important structural differences between the avian and mammalian eyes of potential relevance. Of particular note, the chick eye has a ring of scleral ossicles surrounding and stabilizing the periphery of its cornea, which contributes to ocular accommodation by corneal steepening.58 These structural differences and unique biomechanical properties of the chick cornea compared to the mammalian eye, for which the TonoLab is calibrated, may contribute to the observed overestimations of IOPs recorded with rebound tonometry.59