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Story of the Human Brain
Published in Junichi Takeno, Self-Aware Robots, 2022
An image entering through the lenses of the eyes is inverted when reaching the retinas. There are two types of photoreceptor cells in the retina: cones and rods. The cone cells detect intensity and the rod cells color information. The fovea in the retina is where photoreceptors are most densely concentrated. Signals from the photoreceptors, already image-processed on the retina to some extent, leave the eyes and go to the brain via the part called the blind spot and through a bundle of neural pathways. The blind spot consists of a dense bundle of neural pathways and there are no photoreceptors. The blind spot is therefore “invisible,” or cannot respond to light stimulation. It is very interesting to note that the photoreceptors are viewing light that has penetrated the layers of nerve fiber bundles (from the back side of the nerve cables) since the photoreceptors are located at the deepest part or bottom of the retina (Fig. 3.5).
Medical and Mathematical Background
Published in Arwa Ahmed Gasm Elseid, Alnazier Osman Mohammed Hamza, Computer-Aided Glaucoma Diagnosis System, 2020
Arwa Ahmed Gasm Elseid, Alnazier Osman Mohammed Hamza
The retina is a multi-layered sensory tissue that lies at the back of the eye, and contains millions of photoreceptors that capture light rays and convert them into electrical impulses that will in turn convert them into images in the brain. The main photoreceptors in the retina are rods and cones. Rod cells are very sensitive to changes in contrast, even at low light levels, hence they are able to detect movement, but they are imprecise and insensitive to color located in the periphery of the retina and are used for scotopic vision (night vision). Cones are high precision cells capable of detecting the colors that are concentrated in the macula, the area responsible for photopic vision (day vision). The very central portion of the macula is called the fovea, which is where the human eye is able to best distinguish visual details. The loss of peripheral vision may cause damage to the macula and can result in the loss of central vision.
Nanotechnology Could Revolutionize Therapy for Age-Related Macular Degeneration
Published in Bhupinder Singh, Om Prakash Katare, Eliana B. Souto, NanoAgroceuticals & NanoPhytoChemicals, 2018
Afrah Jalil Abd, Shahdeep Kaur, Ripandeep Kaur, Rupinder Kaur Kanwar, Bhupinder Singh, Jagat Rakesh Kanwar
Blindness and visual impairment are the third most-feared complicated medical conditions, after cardiac diseases and cancer (Fritsche et al., 2014). Worldwide, age-related macular degeneration (AMD), which affects the macula (i.e., peripheral retina) responsible for central vision, is the leading cause of irreversible visual loss among elderly people (Toto et al., 2016). This disorder involves many stages according to its severity, though loss of vision results from photoreceptors’ degeneration and damage to the retinal pigment epithelium (RPE), with these clinical manifestations resembling the advanced stage of disease (Holz et al., 2012). AMD is a multifactorial disease as it gets influenced by several risk factors (Klein et al., 2010). Notably, AMD initiates as a few accumulations of drusen, the biological by-products of the retina cycle, between the retinal pigment epithelium and Bruch's membrane, and progresses gradually to either geographic atrophy or choroidal neovascularization in one or both eyes.
An intelligent approach for detection and grading of diabetic retinopathy and diabetic macular edema using retinal images
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2023
Pranoti Nage, Sanjay Shitole, Manesh Kokare
Diabetic retinopathy (DR) is caused due to a disorder named diabetes mellitus which can damage the retina and even lead to loss of vision. The DR has several stages of severity such as mild, moderate and severe. The severe stage of DR is termed proliferative diabetic retinopathy (PDR) in which the formation of new vessels in the retina is observed (Sugeno et al. 2021). However, the early detection of DR and proper diagnosis will reverse or reduce the growth of the effects caused by the disease (Acharya and Kumar 2021). Diabetic macular oedema (DME) is a condition in which the lesions caused by DR are observed in the middle portion of the retina called the macula. The DME is considered a severe condition as the damages caused by it is irreversible (Lxcamey and Palma 2021). The detection of these diseases is carried out by identifying features such as micro-aneurysms, hard exudates and haemorrhages, as illustrated in Figure 1. The micro-aneurysms refer to the red spots in the retina’s blood vessels with sharp margins, retina’s blood vessels with sharp margins formed in the early stages of the disease (Washburn et al. 2020). The exudates are caused due to abnormalities in the blood vessels which are formed as yellowish-white spots in the outer layer of retina (Wang et al. 2020). The haemorrhages also occur like micro-aneurysms but have irregular margins caused due to the leakage of capillaries which is a delicate blood vessels (Kanimozhi et al. 2021). The blockage of arteries also contributes to a condition named cotton wool spot, which occurs as a white region in the retinal nerve (Chaudhary et al. 2021).
Calculation of Mesopic Luminance Using per Pixel S/P Ratios Measured with Digital Imaging
Published in LEUKOS, 2019
Mikko Maksimainen, Matti Kurkela, Pramod Bhusal, Hannu Hyyppä
The human retina consists of cone cells used for accurate day and color vision and rod cells applied for dark vision. Day vision is also called “photopic vision,” and dark vision is called “scotopic vision.” The sensitivity peaks for photopic and scotopic visions are 555 nm and 507 nm, respectively (CIE 1990; Crawford 1949). Thus, scotopic vision is more sensitive to shorter wavelength (bluish) light, and photopic vision is more sensitive to longer wavelength (reddish) light. However, in the luminance range of 0.005–5.0 cd/m2, partly scotopic and partly photopic vision applies (CIE 2010). This region is known as the “mesopic region,” and the vision for this region is mesopic vision. In the CIE 191 system for mesopic photometry, the mesopic sensitivity curve is calculated as follows:
Recent developments in imaging and surgical vision technologies currently available for improving vitreoretinal surgery: a narrative review
Published in Expert Review of Medical Devices, 2023
Elham Sadeghi, Sashwanthi Mohan, Danilo Iannetta, Jay Chhablani
Degenerative retinal diseases and hereditary conditions, such as age-related macular degeneration and retinitis pigmentosa, involve the photoreceptors and may preserve the inner retina, which contains electrically activated ganglion and bipolar cells. Optic nerve prosthesis and thalamic and cortical intracranial stimulation devices were designed to bypass the retina in profound vision loss and provide artificial images. Recently, the retinal prosthesis, which inserts intraocularly, has received lots of attention. This device consists of an imager that converts the light wavelengths to electrical voltage, electronics that process the image and make an electrical pulse, and multiple microelectrodes that transfer the signal to the inner retina [167,168].