Central nervous system
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha in Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
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.
Lasers in Medicine: Healing with Light
Suzanne Amador Kane, Boris A. Gelman in Introduction to Physics in Modern Medicine, 2020
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.
Optic nerve
Fiona Rowe in Visual Fields via the Visual Pathway, 2016
The intraorbital portion of the optic nerve includes the optic disc and the portion of the optic nerve within the posterior scleral foramen. The optic disc is the commencement of the optic nerve. It is approximately 1.5 mm in diameter and is significantly paler in colour than the surrounding retina. The optic disc is located about 3 mm nasal to and about 0.8 mm above the fovea. It is composed of axons of ganglion cells that leave the eye through the lamina cribrosa. The optic disc is oval in shape and the optic cup is a funnel-shaped depression within the disc where the central retina vessels enter and leave the eye. There are no ganglion cell axons in the optic cup (see Figure 5.1). The layers of the retina and choroid terminate at the edge of the optic disc and the absence of photoreceptors in this area explains the blind spot of the visual field. Posterior to the optic disc, the nerve fibres become myelinated.
Melanocortin 5 Receptor Expression and Recovery of Ocular Immune Privilege after Uveitis
Published in Ocular Immunology and Inflammation, 2022
Tat Fong Ng, Ambika Manhapra, David Cluckey, Yoona Choe, Srujan Vajram, Andrew W. Taylor
Enucleated eyes from EAU mice with or without treatment were fixed in Davidson’s fixative for 24 hours and then transferred to 10% buffered formalin for an additional 24 hours. The eyes were subsequently embedded in paraffin, after which 5-µm sections were cut and stained with H&E. The images were taken using a CX33 microscope (Olympus) and QColor 5 camera system and software (Olympus). Presented are the retinal sections at two optic disk diameters from the center of the optic nerve. Thickness of the retina and the outer nuclear layer (ONL) were measured using ImageJ software of full-length retinal sections centered on the optic nerve (representative images in Supplemental Figure 2). Measurements were made at 0.5, 1.0, 1.5, 2 mm to the right and left (−0.5, −1.0, −1.5, −2 mm) of the optic nerve head.
Diagnosing Optic Disc Drusen in the Modern Imaging Era: A Practical Approach
Published in Neuro-Ophthalmology, 2021
F Costello, SP Rothenbuehler, PA Sibony, S Hamann
Normal retinal blood vessels imaged in cross-section can occasionally be mistaken for ODD on OCT, due to the decreased intravascular reflectivity. The vessels appear in the inner superficial layers of the optic disc. The arteriole-venule pair may be recognised by a ‘figure of eight’ configuration.22 Furthermore, a characteristic vessel wall reflection and shadowing of underlying optic nerve head tissue are distinctive imaging features (Figure 3). Vessels imaged in a longitudinal direction demonstrate a tri-layer profile with decreased intravascular reflectivity. In contrast, vessels imaged more obliquely often demonstrate a hyperdense ‘head’ (without a visible ‘figure of eight’ configuration) and show underlying shadowing. As a practical tip, a long tubular blood vessel can be distinguished from an ODD deposit simply by scrolling through adjacent cross-sectional OCT images to delineate the three-dimensional nature of the optic nerve head structures.
Automatic Assessment of Biometric Parameters in Optic Nerve Head Area by “Zhongshan ONH Calculator (ZOC)”
Published in Current Eye Research, 2019
Fei Li, Kai Yu, Lichun Zhang, Kai Gao, Xinjian Chen, Xiulan Zhang
The ZOC software is integrated with a robust algorithm designed for an ONH structure analysis. A multi-scale graph search method is used to segment three layers on ONH-centered OCT images for both 2D and 3D analysis: the internal limiting membrane (ILM), the photoreceptor inner segment/outer segment (IS/OS) junction, and the lower bound of the retinal pigment epithelium (RPE) complex. For the 2D analysis, the BMO point is user-identified, and a 2D graph search method is used to detect the LC layer in the region below the BMO reference line. For the 3D analysis, a projection image is created by averaging the voxel intensities in the z-direction between the IS/OS junction and Bruch’s membrane surfaces. The optic disk and neuro-retinal rim region are detected on the projection image. The 3D LC surface is detected by applying the graph search method to the specified region below the BMO fitted plane.
Related Knowledge Centers
- Axon
- Cone Cell
- Eye
- Optic Nerve
- Retina
- Rod Cell
- Ganglion
- Retinal Ganglion Cell
- Blind Spot
- Afferent Nerve Fiber