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Introduction to Physiological Regulators and Control Systems
Published in Robert B. Northrop, Endogenous and Exogenous Regulation and Control of Physiological Systems, 2020
Clearly, in the steady state, the AH must exit the eye at the same volume flow rate at which it enters. Outflow of AH is through the canal of Schlemm, into the episcleral veins, then into the main venous circulation, etc. The eyeball is slightly elastic, with most of its compliance coming from the thin, clear cornea. Normal intraocular pressure (IOP) is about 16 mmHg. If there is an increase in the outflow resistance, the normal IOP rises, and if the IOP exceeds its normal high range (about 30 mmHg), the condition known as glaucoma exists. In extreme situations, the IOP can exceed 60 to 80 mmHg. Such acute glaucoma sharply reduces normal arterial blood flow to the retina, causing poor oxygenation and impaired nutrition of retinal neurons and glial cells. If prolonged, glaucoma can lead to the death of retinal neurons, including the loss of retinal ganglion cells which comprise the optic nerve. Such neuron loss is irreversible, and it causes loss of visual acuity and even total blindness.
Introduction
Published in Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe, Visual and Non-Visual Effects of Light, 2020
Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe
Retinal photoreceptors make it possible to gather information passed from the eye to the visual parts of the brain, which analyze and modify this information to form a representation of objects, working in a system of conventional image-forming vision (visual responses to light). Light enters the eye through the cornea, and then through the pupil, whose diameter is controlled by the muscles of the iris. Behind the iris lies the lens, which in conjunction with the cornea focuses the incoming light on the back of the eye, i.e. on the retina, which contains light-sensitive neuron photoreceptors: rods and cones. Photoreceptors are responsible for the process of phototransduction: the conversion of the energy of the sensory stimulus, the photons of light, into an electrical signal – action potential, transmitted and analyzed by the cells of the nervous system. Five general classes of neuron make up the retina. One class, retinal ganglion cells, uses its axons to form the optic nerve, which carries visual information from the eye to the visual brain centers.
Ocular Tonometry
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
Clearly, in the steady state, the AH must exit the eye at the same volume flow rate that it enters. Outflow of AH is through the canal of Schlemm, into the episcleral veins, thence into the main venous circulation, etc. The eyeball is slightly elastic, with most of its compliance coming from the thin, clear cornea. Normal IOP is about 16 mmHg. If there is an increase in the outflow resistance, the normal IOP rises, and if the IOP exceeds its normal high range (about 30 mmHg), the condition known as glaucoma can exist. In extreme situations, the IOP can exceed 60–80 mmHg. Such acute glaucoma sharply reduces normal arterial blood flow to the retina, causing poor oxygenation and impaired nutrition of retinal neurons and glial cells. If prolonged, acute glaucoma can lead to the death of retinal neurons, including the loss of retinal ganglion cells, the axons of which comprise the optic nerve. Such neuron loss is irreversible, and it causes loss of visual field, acuity, and even total blindness. Thus, it is medically important as part of every routine eye examination to measure the IOP, especially in the older patients who are more susceptible to glaucoma.
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
Retinal ganglion cell (RGC) dysfunction and apoptosis is observed in several ocular pathologies including glaucoma [122]. A new molecular imaging technique called DARC (detection of apoptosing retinal cells) has demonstrated neuronal apoptosis in vivo for humans through the use of annexin 5 labeled with fluorescent dye DY-776 (ANX776) in a phase 1 trial with good clinical safety profile and is now being tested in a phase 2 trial (see Figure 7.) [123,124]. Other similar techniques involve the intravitreal injection of TcapQ for in vivo detection of RGC apoptosis. However, this molecule cannot be used in humans unlike the DARC technique [125]. DARC and CapQ can be used for quantitative imaging instrumentation and processing [126]. By quantifying apoptotic RGCs, diagnosis and monitoring of glaucoma as well as other neurodegenerative conditions could be standardized.
Influence of the breathing pattern during resistance training on intraocular pressure
Published in European Journal of Sport Science, 2020
Jesús Vera, Alejandro Perez-Castilla, Beatríz Redondo, Juan Carlos De La Cruz, Raimundo Jiménez, Amador García-Ramos
Glaucoma is characterized by a progressive optic neuropathy that causes the death of retinal ganglion cells and, subsequently, visual loss (Weinreb, Aung, & Medeiros, 2014). Nowadays, glaucoma affects more than 70 million people worldwide and it is estimated to increase to approximately 110 million by 2040 (Tham et al., 2014). Reduction of intraocular pressure (IOP) is the only proven method to treat glaucoma, and pressure-lowering medications are the mainstay treatment for this disease (Heijl et al., 2002). However, IOP values should be reduced using as little medication as possible to minimize side effects (Yee, 2007). In this regard, daily life activities such as food intake (Giaconi et al., 2012; Kang et al., 2016), sleeping position (Prata, De Moraes, Kanadani, Ritch, & Paranhos, 2010), caffeine intake (Li, Wang, Guo, Wang, & Sun, 2011; Vera, Redondo, Molina, Bermúdez, & Jiménez, 2019), smoking (Chan et al., 2016) or the practice of physical exercise (Zhu et al., 2018) have also demonstrated to affect IOP values.
Evaluation of potential health effects associated with occupational and environmental exposure to styrene – an update
Published in Journal of Toxicology and Environmental Health, Part B, 2019
M.I. Banton, J.S. Bus, J.J. Collins, E. Delzell, H.-P. Gelbke, J.E. Kester, M.M. Moore, R. Waites, S.S. Sarang
Vettori et al. (2000) examined the effect of subchronic styrene inhalation exposure on amacrine cells in female Sprague-Dawley rats. Amacrine cells, of which there are several dozen types, are interneurons that serve to integrate inputs from photoreceptors and modulate the visual message presented to retinal ganglion cells (Schwartz 2010; Witkovsky 2004). Vettori et al. (2000) focused on amacrine cells that release dopamine, the most abundant catecholamine in the vertebrate retina. Dopamine has multiple trophic roles related to eye growth, cell viability, circadian rhythmicity, and color perception (Kim, Chen, and Tannock 2014; Schwartz 2010; Tannock, Banaschewski, and Gold 2006; Witkovsky 2004). These neurons begin to die in aging animals, and reduction in retinal dopamine, such as occurs in Parkinson’s disease and attention-deficit/hyperactive disorder (ADHD), results in reduced visual contrast sensitivity (CS) and color vision deficits, particularly in blue-yellow pathways (Djamgoz et al. 1997; Firsov and Astakhova 2016; Popova 2014; Tannock, Banaschewski, and Gold 2006; Witkovsky 2004). Morphometric analysis of retinas from female Sprague-Dawley rats exposed to 300 ppm styrene 6 hours/day, 5 days/week, for 12 weeks (n = 10) showed a significant loss of tyrosine hydroxylase-immunoreactive (dopamine-producing) amacrine cells (Vettori et al. 2000). Dopamine and glutathione content were significantly lower in treated animals, and the activity of tyrosine hydroxylase was significantly higher when expressed as a function of the number of dopaminergic amacrine cells (Vettori et al. 2000). The potential human significance of these findings is unknown.