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Chapter 3 Physics of the Senses
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
The following anatomical description of the eye is based on that of Marieb (1991), although errors are our own! The basic structure of the eye is much like that of a football. The wall of the eyeball consists of three layers, called tunics. The only interruption of these tunics is in the posterior portion where the optic nerve enters the eye. The outermost layer is a fibrous tunic composed of dense connective tissue. Its two components are the cornea and the sclera. The cornea, at the front of the eye, has its collagen fibres regularly arranged, and it is transparent. It is curved, and represents the first of the focusing components of the eye. It does not contain blood vessels (and can therefore be transplanted with relatively little risk of rejection), but does contain nerve fibres and is sensitive to irritation. The sclera, or white of the eye, is a tough, opaque sheath to which the muscles of the eye are connected. The next layer is a vascular tunic called the uvea. Its three components are the choroid, the ciliary body, and the iris. The choroid contains a large number of small blood vessels, supplying the other tunics as well as itself. It also contains pigments that help to prevent reflection of light within the eye, which would tend to blur the images registered. The ciliary body contains the muscles that support and focus the lens, and also the capillaries that secrete fluid into the anterior segment of the eyeball. The iris is the characteristically coloured part of the eye. Its musculature is constructed to allow a change in the diameter, from about 1.5 to 8 mm, of the central aperture, the pupil, thus controlling the amount of light that can enter the posterior segment. Circumferentially orientated muscles contract the pupil and radially orientated ones expand it.
Repeatability and reproducibility of anterior lens zonule length measurement using ArcScan insight 100 very high-frequency ultrasound
Published in Expert Review of Medical Devices, 2023
Zehui Zhu, Han Zou, Hongzhe Li, Xueer Wu, Yiyi Wang, Zhangliang Li, Yune Zhao
Most published studies using the Insight 100 have focused on phakic IOL implantation. Accurate measurements of the anterior eye segment’s anatomy play a critical role in selecting the appropriate IOL size before surgery [6,10,11]. Anterior segment optical coherence tomography (AS-OCT) and ultrasound devices are utilized for measuring various anterior segment structural parameters, including anterior chamber depth, anterior chamber angle distance, sulcus-to-sulcus, and other relevant metrics. AS-OCT enables swift image acquisition and high-resolution scans. However, it is limited by its inability to display the ciliary body, ciliary sulcus, and the complete space between the iris and the crystalline lens with clarity. In comparison to AS-OCT, the Insight 100 examination procedure is notably more intricate and requires additional time. However, the primary benefit of utilizing Insight 100 is its ability to produce highly precise images of the entire anterior ocular segment, which includes the ciliary muscle, the equator of the lens, and the posterior lens capsule.
Therapeutic challenges in ocular delivery of lipid based emulsion
Published in Egyptian Journal of Basic and Applied Sciences, 2018
Rahul Tiwari, Vikas Pandey, Saket Asati, Vandana Soni, Dharmendra Jain
The eye is a spherical structure which consisting of three protecting layers i.e.; the outer layer sclera, the middle layer choroid which include, ciliary body and iris and the inner nervous tissue layer called retina. The sclera is dense, white, and continuous with tough fibrous coating that protects the inner layer [18].The choroid layer of blood vessels between the retina and sclera situated inside the sclera contains many blood vessels and is modified the front of the eye as pigmented iris [19]. The iris the colored part of the eye (in shades of blue, green, brown, hazel, or grey) regulate the entry of light and sharpen focus and allows nourishment from the vitreous to nourish the cornea. Fig. A1 shows that mainly blood aqueous barrier, blood retinal barrier, Corneal barrier, are limits the ocular BA of topical formulations.
Anterior Segment Optical Coherence Tomography in Pediatric Ocular Pathology: Imaging Study of 115 eyes
Published in Expert Review of Medical Devices, 2023
The anterior chamber depth and configuration; a detailed assessment of the anterior chamber angle structures, including the iris root, angle recess, Schlemm’s canal, scleral spur, in some cases anterior ciliary body and anterior trabecular meshwork were done. Anterior chamber cells, exudate, and hyphema could be visualized as well as synechiae of the iris with the lens and cornea. Abnormal angle tissue and iris pathology, including flattening, tears, holes, and iridodialyses, were examined as well. Post-operative pseudophakic children or trauma cases were also evaluated in order to monitor intraocular lens (IOL) position and surgical integrity.