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Designing for Head and Neck Anatomy
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
The eye is an approximate sphere with a 2.5 cm (1 in.) diameter (Forrester, Dick, McMenamin, Roberts, & Pearlman, 2016, p. 13). Refer to Figure 3.7 to study eye structures. When you look at a person’s face you see just a portion of the white sclera of the eyeball surrounding the colored iris and the dark central pupil. The cornea, the clear front window of the eye, lies in front of the iris and the structurally deeper crystalline lens. The sclera, but not the cornea, is covered by the conjunctiva, a thin mucous membrane which is the outermost layer of the exposed eyeball and contiguous with the inner layer of the eyelid. It effectively prevents the migration of small foreign bodies or liquids into the eye socket and the cranium. The eyeball is not one fluid-filled balloon-like structure. It actually has three chambers. The anterior chamber lies between the cornea and the iris and bulges slightly under the upper and lower eyelids. The smaller posterior chamber lies between the iris and the crystalline lens. The fluid in these two chambers is called the aqueous humor. The third chamber, the vitreous chamber, between the crystalline lens and the retina, at the posterior of the eye, holds a more viscous fluid, the vitreous humor.
The Mechanobiology of Aqueous Humor Transport across Schlemm's Canal Endothelium
Published in Jiro Nagatomi, Eno Essien Ebong, Mechanobiology Handbook, 2018
Intraocular pressure (IOP) is controlled by the turnover of aqueous humor, a clear fluid that fills the anterior segment of the eye and serves to nourish the avascular tissues of the cornea, lens, and trabecular meshwork (Figure 21.1). Aqueous humor is secreted into the posterior chamber by the ciliary processes, enters the anterior chamber through the pupil, and drains through one of two outflow pathways. The conventional or trabecular outflow pathway carries the majority of outflow and includes the trabecular meshwork, Schlemm's canal, and downstream collecting vessels that lead to the episcleral veins. The secondary uveoscleral outflow pathway appears to account for only 3%–35% of total outflow in the human eye (as surveyed by Nilsson [1]) and likely contributes little toward IOP regulation, although uveoscleral outflow does become important for glaucoma therapies involving prostaglandins and its analogues.
Central nervous system
Published in A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha, Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha
The aqueous humour is a clear watery fluid that fills the anterior chamber. The lens is a biconvex transparent structure assisting in the focusing of light onto the retina and separates the anterior and posterior chambers. The vitreous humour occupies the posterior chamber and together with the aqueous humour acts as a refractive medium, maintaining the shape of the eyeball, and helps to hold the retina in contact with the choroid. The optic nerve is formed at the optic disc and leaves the orbital cavity via the optic foramen to the middle cranial fossa.
Anterior Segment Optical Coherence Tomography in Pediatric Ocular Pathology: Imaging Study of 115 eyes
Published in Expert Review of Medical Devices, 2023
Optical coherence tomography (OCT) is a noninvasive, rapid investigative imaging modality that provides intricate micron-resolution three-dimensional images for the diagnosis and monitoring of both anterior and posterior segment disorders. It utilizes infrared light reflected by the ocular structures to create high-resolution cross-sectional images [1]. Anterior segment OCT (AS-OCT) is a rapidly emerging technology that provides high-resolution images of the structures constituting the anterior segment, especially the cornea, ocular surface, angle of the anterior chamber, iris, lens, and any pathology pertaining to the anterior segment can be viewed in extreme detail, provided the media is sufficiently clear. It can also be used as a measuring tool for corneal thickness, anterior and posterior chamber depths, anterior chamber diameter, chamber angle configuration, and even iris and lens thicknesses. It can help immensely in the diagnosis and monitoring of anterior segment disorders by providing useful information about pediatric ocular anterior segment disease [1–5].
EVO/EVO+ Visian Implantable Collamer Lenses for the correction of myopia and myopia with astigmatism
Published in Expert Review of Medical Devices, 2023
Elena Martínez-Plaza, Alberto López-de la Rosa, Alberto López-Miguel, Alfredo Holgueras, Miguel J. Maldonado
The Visian Implantable Collamer Lens (ICL; (STAAR Surgical, Monrovia, California, USA) is a posterior chamber phakic intraocular lens implanted between the iris and the crystalline lens. After the first prototypes, advanced ICL models have been designed, from the previous models (V1, V2, V3, and V4) to the current available ones, V4b, V4c, and V5 [14]. The implantation of the V4b, as well as the previous models, requires a peripheral iridotomy to facilitate aqueous humor flow. At present, this model is solely used for the correction of hyperopia and hyperopic astigmatism. On the other hand, the V4c (also known as EVO) and the V5 (EVO+) models have been designed with a central hole (KS-Aquaport) avoiding the need for iridotomy (Figure 1) [15]. Both models are available for compensating myopia and myopic astigmatism. The main difference between EVO and EVO+ is the higher optical diameter zone design in the EVO+ model, allowing to achieve better quality of vision, especially under low lighting conditions [16].