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The retina is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera.
Floaters or eye floaters are sometimes visible deposits within the eye's vitreous humour, which is normally transparent, or between the vitreous and retina. They can become particularly noticeable when looking at a blank surface or an open monochromatic space, such as blue sky. Each floater can be measured by its size, shape, consistency, refractive index, and motility. They are also called muscae volitantes, or mouches volantes. The vitreous usually starts out transparent, but imperfections may gradually develop as one ages. The common type of floater, present in most people's eyes, is due to these degenerative changes of the vitreous. The perception of floaters, which may be annoying or problematic to some people, is known as myodesopsia, or, less commonly, as myodaeopsia, myiodeopsia, or myiodesopsia. It is not often treated, except in severe cases, where vitrectomy (surgery), laser vitreolysis, and medication may be effective.
Night vision is the ability to see in low-light conditions, either naturally with scotopic vision or through a night-vision device. Night vision requires both sufficient spectral range and sufficient intensity range. Humans have poor night vision compared to many animals such as cats, in part because the human eye lacks a tapetum lucidum, tissue behind the retina that reflects light back through the retina thus increasing the light available to the photoreceptors.
Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet (UV) rays from either natural or artificial sources. Photokeratitis is akin to a sunburn of the cornea and conjunctiva.
The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories:
Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cones function best in relatively bright light, called the photopic region, as opposed to rod cells, which work better in dim light, or the scotopic region. Cone cells are densely packed in the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina. Conversely, they are absent from the optic disc, contributing to the blind spot. There are about six to seven million cones in a human eye, with the highest concentration being towards the macula.
A stun grenade, also known as a flash grenade, flashbang, thunderflash or sound bomb, is a less-lethal explosive device used to temporarily disorient an enemy's senses. It is designed to produce a blinding flash of light of around 7 megacandela (Mcd) and an intensely loud "bang" of greater than 170 decibels (dB). It was first used by the British Army's Special Air Service in the late 1970s.
Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a surgical emergency.
Laser radiation safety is the safe design, use and implementation of lasers to minimize the risk of laser accidents, especially those involving eye injuries. Since even relatively small amounts of laser light can lead to permanent eye injuries, the sale and usage of lasers is typically subject to government regulations.
A laser pointer or laser pen is a small handheld device with a power source and a laser diode emitting a very narrow coherent low-powered laser beam of visible light, intended to be used to highlight something of interest by illuminating it with a small bright spot of colored light.
Hemeralopia is the inability to see clearly in bright light and is the exact opposite of nyctalopia, the inability to see clearly in low light. Hemera was the Greek goddess of day, and Nyx was the goddess of night. However, it has been used in an opposite sense by many non-English-speaking doctors. It can be described as insufficient adaptation to bright light. It is also called "heliophobia" and "day blindness".
Retinal hemorrhage is a disorder of the eye in which bleeding occurs in the retina, the light sensitive tissue, located on the back wall of the eye. There are photoreceptor cells in the retina called rods and cones, which transduce light energy into nerve signals that can be processed by the brain to form visual images. Retinal hemorrhage is strongly associated with child abuse in infants and young children and often leaves such abused infants permanently blind. In older children and adults, retinal hemorrhage can be caused by several medical conditions such as hypertension, retinal vein occlusion, anemia, leukemia or diabetes.
A dazzler is a non-lethal weapon which uses intense directed radiation to temporarily disorient its target with flash blindness. They can effectively deter further advances, regardless of language or cultural barriers, but can also be used for hailing and warning. Targets can include electronic sensors as well as human vision.
Photopsia is the presence of perceived flashes of light in the field of vision.
Coats' disease is a rare congenital, nonhereditary eye disorder, causing full or partial blindness, characterized by abnormal development of blood vessels behind the retina. Coats' disease can also fall under glaucoma.
A welding helmet is a type of personal protective equipment used in performing certain types of welding to protect the eyes, face, and neck from flash burn, sparks, infrared and ultraviolet light, and intense heat. The modern welding helmet used today was first introduced in 1937 by Willson Products.
Under certain conditions, laser light or other bright lights directed at aircraft can be a hazard. The most likely scenario is when a bright visible laser light causes distraction or temporary flash blindness to a pilot, during a critical phase of flight such as landing or takeoff. It is far less likely, though still possible, that a visible or invisible beam could cause permanent harm to a pilot's eyes. Although laser weapons are under development by armed forces, these are so specialized, expensive and controlled that it is improbable for non-military lasers to cause structural damage to an aircraft.
On 4 April 1997, a Canadian Armed Forces helicopter was allegedly illuminated by a laser while observing the Russian merchant ship and suspected spy vessel Kapitan Man, which was in the Strait of Juan de Fuca in U.S. territorial waters near Port Angeles, Washington. The Canadian Air Force pilot and the U.S. Navy passenger, who was taking photographs of the ship, reportedly suffered eye pain and injuries consistent with laser exposure. However, subsequent investigations into the incident were unable to verify that any lasing had occurred.
Retinal migraine is a retinal disease often accompanied by migraine headache and typically affects only one eye. It is caused by ischaemia or vascular spasm in or behind the affected eye.
Photic retinopathy is damage to the eye's retina, particularly the macula, from prolonged exposure to solar radiation or other bright light, e.g., lasers or arc welders. The term includes solar, laser, and welder's retinopathy and is synonymous with retinal phototoxicity. It usually occurs due to staring at the Sun, watching a solar eclipse, or viewing an ultraviolet, Illuminant D65, or other bright light.[1]
References
- ↑ "Laser Pointers: Their Potential Affects[sic] on Vision and Aviation Safety (April 2001)FAA" (PDF). Archived from the original (PDF) on June 26, 2013. Retrieved September 10, 2006.
- ↑ Kulur, Malvika. "Causes and Risks of Flash Blindness". buzzle.com. Buzzle. Retrieved 3 March 2018.
- ↑ first strike(DOD) The first offensive move of a war. (Generally associated with nuclear operations.) Archived September 10, 2005, at the Wayback Machine
- ↑ BMJ No 7120 Volume 315 Editorial, 29 November 1997 Blinding laser weapons still available on the battlefield
- ↑ FAA Order JO 7400.2L, Procedures for Handling Airspace Matters, effective 2017-10-12 (with changes), accessed 2017-12-04
- ↑ Byrnes, V. A. (1953). Flash Blindness. Operation SNAPPER. Nevada Proving Grounds, April–June 1952, Project 4.5. School of Aerospace Medicine. Brooks A.F.B. Texas.
- ↑ Flashblindness | Effects of Nuclear Weapons | atomicarchive.com
- ↑ BBC NEWS Tuesday, 17 August, 1999, 16:13 GMT 17:13 UK Safety in sight total eclipse 300