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Lasers in Medicine: Healing with Light
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The anatomy of the eye is shown in Figure 3.30a. The white of the eye is called the sclera. Light enters the eye through the cornea and the pupil, the opening of the iris. It then passes through the lens and the vitreous humor, a jellylike substance that fills the eyeball, and falls upon the inner lining of the eyeball, called the retina. Both the cornea and the lens refract entering rays of light in such a way as to project tiny images of the outside world onto the retina, which plays a role analogous to the image sensor in a camera. The retina is a complex structure consisting of many specialized layers, including the pigment epithelium, which contains specialized cells for sensing light, and choroid, which contains blood vessels and dark blue pigments to absorb stray light. Some layers hold the rod and cone cells that actually sense light, some provide circulation and support. In the regions of the retina known as the fovea and the macula, or yellow spot, visual acuity is highest because of a high concentration of light-sensing cells. The optic disc, or blind spot, is where the optic nerve enters the retina. Preserving the functioning of these regions is of especial concern during laser surgery.
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 eye is the special sense organ of sight (Figs 11.52a,b). It is situated in the orbital cavity, surrounded by adipose tissue that affords protection from trauma. It is almost spherical with an anterior bulge, comprising three layers: an outer fibrous layer, a middle vascular layer and an inner nervous layer. It contains three substances: the aqueous humour, the lens and the vitreous humour. The outer fibrous layer forms a complete sphere, the anterior one-sixth is known as the cornea and the posterior five-sixths the sclera. It has no blood supply but derives its nourishment from lymph. The middle vascular layer forms nine-tenths of a sphere incomplete anteriorly. It comprises the choroid, ciliary body and the iris. The innermost layer forms three-quarters of a sphere (posteriorly) and is known as the retina. This has an outer pigmented layer and an inner nervous layer. It contains special cells designed for vision – rods and cones. The optic disc (or blind spot) is that part of the retina where the optic nerve enters the eyeball.
Computer and Human Vision Systems
Published in Sheila Anand, L. Priya, A Guide for Machine Vision in Quality Control, 2019
The optic nerve is a grouping of nerve fibers that connects the eye to the brain and transmits the visual signals to the brain. The optic nerve is mainly composed of retinal ganglion cell (RGC) axons. The optic disc is the specific region of the retina where the optic nerve and blood vessels pass through to connect to the back of the eye. This area is known as the anatomical blind spot of the eye, but it is not perceptible as the brain compensates for this. The optic nerve is a part of the eye as well as a part of the central nervous system.
Abusive head trauma in India: imaging raises the curtain
Published in International Journal of Injury Control and Safety Promotion, 2022
Hima Pendharkar, Shumyla Jabeen, Nupur Pruthi, K. V. L. N Narasinga Rao, Dhaval Shukla, Nitish Kamble, Kavita V. Jangam, John Vijay Sagar Kommu, Thennarasu Kandavel, Senthil Amudhan
Retinal hemorrhages are ophthalmological findings strongly associated in children suspected of abuse with most large studies identifying RH in 70–80% of confirmed AHT cases. The RH’s in AHT are characteristically bilateral, multiple, extend to the retina’s periphery and are found in all retinal layers. On the other hand, RH in non-AHT are usually unilateral, few in number and located at the posterior pole. One must note that while there are features of RH that are undoubtedly strongly indicative of AHT, there is no pattern that is pathognomonic to either condition (A. M. Kemp, 2011). Visual impairment has been described as a permanent and long-term complication of AHT (Harcourt & Hopkins, 1971; Mushin, 1971). One of our patients (case shown in Figure 3) presented with vision loss which on ophthalmologic examination revealed bilateral pale optic disc with attenuation of arteries probably due to consecutive optic atrophy.
Fast optic disc segmentation using FFT-based template-matching and region-growing techniques
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2018
N. D. Salih, Marwan D. Saleh, C. Eswaran, Junaidi Abdullah
Optic disc (OD) represents the portion of the retina where the optic nerve and the retinal and choroidal vessels emerge into the eye (Mahfouz & Fahmy 2010). OD is characterised by its bright nature, yellowish colour, slightly oval/elliptical shape. According to Sinthanayothin et al. (1999), OD occupies about one-seventh of the entire image. However, other authors have indicated that the size of OD varies from one person to another, occupying about one-tenth to one-fifth of the image (Li & Chutatape 2001; Aquino et al. 2010). Among the diseases mentioned above, GC which is considered as the second leading cause of blindness worldwide is the most relevant to the OD segmentation since it causes cupping of the optic nerve head and visual field loss (Tielsch et al. 1991; Lee et al. 2010). Besides the diagnosis of GC, OD detection serves as a landmark for estimating the location of other anatomical structures such as the fovea (centre of macula) due to the fact that an approximately constant distance exists between the OD and the latter (Sinthanayothin et al. 1999; Gagnon et al. 2001; Youssif et al. 2008). OD can also be used as a useful clue in several methods for retinal vasculature tree tracking. Furthermore, OD detection contributes to the automatic detection of other retinal abnormalities, especially those associated with DR, such as exudates, drusen, and haemorrhages (Hsu et al. 2001; Sbeh et al. 2002; Lu & Lim 2011). The OD can incorrectly be classified as one of these spot lesions due to their similarity in terms of brightness, yellowish colour, depth, shape, etc. Removing the OD therefore improves the correct identification of exudate regions and decreases false positives (FPs) (Osareh et al. 2003; Youssif et al. 2008).
Structural feature analysis of the vascular network in retinal images
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2019
O. Bandyopadhyay, T. Dutta, N. Dutta, A. Biswas, B. B. Bhattacharya
The retina consists of approximately one million nerve fibres, which group together to form optic nerves. The region in the retina where nerve fibres come together to form the optic nerve is called the optic disc (OD), which is circular in shape and visibly bright in the fundus images. The appearance of retina in normal fundus images is transparent, and the retinal arterioles and venules spread in the nerve fibre layer of the retina (Marry et al. 2016). Thus, the vascular network structure in fundus image is a rich network of blood vessels (arteries and veins), bifurcation points of the blood vessels and optic disc region.