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Imaging the Living Eye
Published in Margarida M. Barroso, Xavier Intes, In Vivo, 2020
Brian T. Soetikno, Lisa Beckmann, Hao F. Zhang
As shown in Figure 14.1C, the retina is composed of eight distinct layers grouped into the outer and inner retinae. The outer retina consists of photoreceptors and the retinal pigment epithelium (RPE). Photoreceptors are further divided into rod and cone photoreceptors, which are responsible for low-light vision and color perception, respectively. The RPE layer contains various pigments, including melanin, that aid in absorbing irradiating light energy among other physiological roles. In addition, the RPE also transports nutrients between the photoreceptors and the choriocapillaris, participates in the visual cycle, removes shed photoreceptor membranes by phagocytosis, and secretes a variety of growth factors (Strauss, 2005). The inner retina consists of four classes of neurons: ganglion cells, amacrine cells, horizontal cells, and bipolar cells. The combination and connections of these cells form small neuronal networks that amplify, process, and filter information from the photoreceptors (Wassle, 2004). Eventually, the ganglion cell bodies collect the partially processed information, and their axons, which together form the optic nerve, transmit the information to the visual cortex of the brain for further higher-level information processing.
The New Maximum Permissible Exposure
Published in Barat Ken, Laser Safety Tools and Training, 2017
The function of the eye optics is to image the external world onto the retinal photoreceptors at the focal plane at the back of the eye. Geometric optics then dictate that a collimated laser beam, incident at the cornea, will be focused onto a very small area at the retina: the diameter of that area is limited by the quality of the eye optics and the state of accommodation at the time of the exposure. Immediately posterior to the photoreceptors, and still at the focus of the eye optics, lays the retinal pigment epithelium (RPE), a monolayer of cells containing melanin granules. Melanin is a very strong absorber of optical radiation to the extent that most of the radiation incident on the retina is absorbed in a 5-μm layer of melanin granules. Thus, the collimated laser beam incident at the cornea is concentrated onto a strongly absorbing layer at the retina and injury at that layer results from very small levels of energy incident at the cornea (Figure 11.2).
Terpenoids: The Biological Key Molecules
Published in Dijendra Nath Roy, Terpenoids Against Human Diseases, 2019
Moumita Majumdar, Dijendra Nath Roy
Carotenoids play a key role in damage repair in the eyes. The retina has retinal pigment epithelial (RPE) cells, which are responsible for all functional coordination by maintaining retinal homeostasis. In several diseases, including diabetes, a vitamin A deficiency creates oxidative stress in RPE cells, leading to macular damage accompanied by some vascular dysfunctions of the eye.
Recent advances in imaging technologies for assessment of retinal diseases
Published in Expert Review of Medical Devices, 2020
Taha Soomro, Neil Shah, Magdalena Niestrata-Ortiz, Timothy Yap, Eduardo M. Normando, M. Francesca Cordeiro
The sO2 has been shown to be abnormal in a number of ophthalmic conditions such as glaucoma [70], retinal vascular occlusion [71] and diabetic retinopathy [72]. RPE melanin loss contributes to age-related macular degeneration (AMD) progression [73].