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Conducting Polymers for Ophthalmic Applications
Published in Ram K. Gupta, Conducting Polymers, 2022
The posterior segment has three layers as sclera, choroid, and retina, as well as a vitreous cavity filled with vitreous humor. The sclera is the external white shell of the eye and serves as a protective layer with the eyelids as well as helps in the preservation of the eye's form by giving mechanical support. The hydrophobicity and charge of the molecules are critical parameters for drug molecule penetration through the sclera. The high surface area and relatively permeable nature of the sclera make it suitable for researches in drug delivery to the posterior segment [6]. The choroid is the middle layer of the eyeball, with a dense vascular system and maintains the temperature of the eye medium and feeds the inner layer. The retina is the innermost layer of the eye and is primarily responsible for vision. The incoming light is transformed into an electrical signal by specialized neurons called photoreceptors in the retina (i.e., rods and cones) then delivered to the brain for image formation.
Clinical Photodynamic Therapy: The Continuing Evolution
Published in Barbara W. Henderson, Thomas J. Dougherty, Photodynamic Therapy, 2020
Thus, PDT appears to have good promise for the treatment of ocular melanomas of ≤ 1000 mm3 volume [112]. It has been suggested that an alternate method of ocular melanoma treatment involve treatment of the choroid surrounding the tumor to close off the choroidal blood supply, rather than concentrating on direct light treatment of the tumor itself [111]. Although the collective data suggest that high light doses (in excess of 1000 or 2000 J/cm2), might be optimal for treatment of melanoma, clinical trials for dose-ranging studies are required to test this possibility. The fact that melanoma tends to be a heavily pigmented tissue and, thus, attenuates light rapidly over a short distance is supported by the complete response seen in amelanotic melanoma at a light dose that produced only partial responses, at best, in pigmented melanomas [111]. Development of devices specific for delivery of light to ocular structures may be able to increase the complete response rates seen for ocular melanoma.
Computer and Human Vision Systems
Published in Sheila Anand, L. Priya, A Guide for Machine Vision in Quality Control, 2019
The retina is the light-sensitive membrane that lines the inner surface of the back of the eyeball. Images are formed on the retina and it transmits those visual messages to the brain using electrical signals. Ora serrata is a special structure that demarcates the sensitive part of retina from its non-sensory part. This layer lies close to the choroid and consists of a single layer of cells containing the pigment. The choroid lies between the sclera and the retina. It supplies the blood vessels that nourish the outer two-thirds of the retina. The space between the lens and retina is covered by a transparent colorless fluid known as vitreous humor or simply as vitreous. The vitreous humor is fluid-like near the center, and gel-like near the edges. It is surrounded by a layer of collagen, called vitreous membrane, that separates it from the rest of the eye. With age, the vitreous humor begins to shrink and problems like posterior retinal detachment or retinal tears occur.
Thermal analysis of intraocular electronic display projector visual prosthesis
Published in Numerical Heat Transfer, Part A: Applications, 2020
D. Gongal, S. Thakur, A. Panse, R. Pawar, C. Q. Yu, C. D. Foster
Heat transfer in the eye is mainly through conduction, with convection, evaporation, and radiation also playing roles. There is a convection heat transfer from the anterior part of the eye exposed to the surrounding air and from the posterior sclera region to the body. Heat is lost from the corneal surface through radiation and evaporation of tear film. The flow of aqueous humor inside the eye also transfers heat between the anterior and posterior regions of the eye. However, the effect is negligible [15]. The blood flow in the choroidal region helps to thermoregulate the eye temperature. In this study, we have not taken into account the effect of blood perfusion.