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125-762: NEI was established in 1968 as the nation's leading supporter of eye health and vision research projects. These projects include basic science research into the fundamental biology of the eye and the visual system . NEI also funds translational and clinical research aimed at developing and testing therapies for eye diseases and disorders. This research is focused on developing therapies for leading causes of vision loss including glaucoma , diabetic retinopathy , age-related macular degeneration (AMD), cataract , myopia and amblyopia . NEI also funds research on many other causes of vision loss including retinitis pigmentosa , uveitis , retinal detachment , and rare eye diseases and disorders. Since its founding, NEI has supported

250-455: A fovea area which gives acute vision. In the acute zone, the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. The black spot that can be seen on the compound eyes of such insects, which always seems to look directly at the observer, is called a pseudopupil . This occurs because the ommatidia which one observes "head-on" (along their optical axes ) absorb

375-465: A central band known as the visual streak. Around the fovea extends the central retina for about 6 mm and then the peripheral retina. The farthest edge of the retina is defined by the ora serrata . The distance from one ora to the other (or macula), the most sensitive area along the horizontal meridian , is about 32 mm. In section, the retina is no more than 0.5 mm thick. It has three layers of nerve cells and two of synapses , including

500-460: A central point. The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out. Many small organisms such as rotifers , copepods and flatworms use such organs, but these are too small to produce usable images. Some larger organisms, such as scallops , also use reflector eyes. The scallop Pecten has up to 100 millimetre-scale reflector eyes fringing

625-428: A cluster of numerous ommatidia on each side of the head, organised in a way that resembles a true compound eye. The body of Ophiocoma wendtii , a type of brittle star , is covered with ommatidia, turning its whole skin into a compound eye. The same is true of many chitons . The tube feet of sea urchins contain photoreceptor proteins, which together act as a compound eye; they lack screening pigments, but can detect

750-579: A considered view that the bird retina depends for nutrition and oxygen supply on a specialized organ, called the "pecten" or pecten oculi , located on the blind spot or optic disk. This organ is extremely rich in blood vessels and is thought to supply nutrition and oxygen to the bird retina by diffusion through the vitreous body. The pecten is highly rich in alkaline phosphatase activity and polarized cells in its bridge portion – both befitting its secretory role. Pecten cells are packed with dark melanin granules, which have been theorized to keep this organ warm with

875-474: A discrete academic discipline beyond surgery and neurology . This prompted some leading academic ophthalmologists and vision community supporters to campaign for a separate institute focused solely on vision research. These advocates included Bernard Becker, M.D. ; A. Edward Maumenee, M.D. ; David Glendenning Cogan, M.D. ; Frank Newell, M.D.; Michael J. Hogan, M.D.; Frank C. Winter, M.D.; John M. McLean, M.D.; and Jules Stein, M.D. The lobbying campaign for

1000-434: A focus on individuals and populations at higher risk of eye health disorders, including older people, those with diabetes, Black/African American people, and Hispanic/Latino people. The program also draws on research supported by NIH and NEI to identify other populations at risk (e.g., Asian American people, residents of rural communities) and to produce educational materials for professional and public audiences. It emphasizes

1125-518: A full 360° field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera , have compound eyes of only a few facets, each with a retina capable of creating an image. With each eye producing a different image, a fused, high-resolution image is produced in the brain. The mantis shrimp has the world's most complex colour vision system. It has detailed hyperspectral colour vision. Trilobites , now extinct, had unique compound eyes. Clear calcite crystals formed

1250-612: A high refractive index, decreasing to the edges; this decreases the focal length and thus allows a sharp image to form on the retina. This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration . Such a non-homogeneous lens is necessary for the focal length to drop from about 4 times the lens radius, to 2.5 radii. So-called under-focused lens eyes, found in gastropods and polychaete worms, have eyes that are intermediate between lens-less cup eyes and real camera eyes. Also box jellyfish have eyes with

1375-403: A lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium . The second type is named the superposition eye. The superposition eye is divided into three types: The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to

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1500-447: A limit on the possible resolution that can be obtained (assuming that they do not function as phased arrays ). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require very large compound eyes, around 11 metres (36 ft) in radius. Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form

1625-509: A linear model, this response profile is well described by a difference of Gaussians and is the basis for edge detection algorithms. Beyond this simple difference, ganglion cells are also differentiated by chromatic sensitivity and the type of spatial summation. Cells showing linear spatial summation are termed X cells (also called parvocellular, P, or midget ganglion cells), and those showing non-linear summation are Y cells (also called magnocellular, M, or parasol retinal ganglion cells), although

1750-403: A more complex structure such as the inverted retina can generally come about as a consequence of two alternate processes - an advantageous "good" compromise between competing functional limitations, or as a historical maladaptive relic of the convoluted path of organ evolution and transformation. Vision is an important adaptation in higher vertebrates. A third view of the "inverted" vertebrate eye

1875-451: A parabolic mirror to focus the image; it combines features of superposition and apposition eyes. Another kind of compound eye, found in males of Order Strepsiptera , employs a series of simple eyes—eyes having one opening that provides light for an entire image-forming retina. Several of these eyelets together form the strepsipteran compound eye, which is similar to the 'schizochroal' compound eyes of some trilobites . Because each eyelet

2000-416: A pit to reduce the angle of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. Eyes enable several photo response functions that are independent of vision. In an organism that has more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to

2125-420: A pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eyes". They are small, comprising up to about 100 cells covering about 100 μm. The directionality can be improved by reducing the size of the aperture, by incorporating

2250-498: A reflective layer behind the receptor cells, or by filling the pit with a refractile material. Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates (see infrared sensing in snakes ). However, pit organs are fitted with receptors rather different from photoreceptors, namely a specific transient receptor potential channel (TRP channels) called TRPV1 . The main difference

2375-466: A refractive cornea: these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution. In the eyes of most mammals , birds , reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air. In general, the lens is not spherical. Spherical lenses produce spherical aberration. In refractive corneas,

2500-617: A resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes , so are better suited to dark-dwelling creatures. Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being ciliated (as in the vertebrates) or rhabdomeric . These two groups are not monophyletic; the Cnidaria also possess ciliated cells, and some gastropods and annelids possess both. Some organisms have photosensitive cells that do nothing but detect whether

2625-461: A result, the useful lifetime of photoreceptors in invertebrates is much shorter than in vertebrates. Having easily replaced stalk eyes (some lobsters) or retinae (some spiders, such as Deinopis ) rarely occurs. The cephalopod retina does not originate as an outgrowth of the brain, as the vertebrate one does. This difference suggests that vertebrate and cephalopod eyes are not homologous , but have evolved separately. From an evolutionary perspective,

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2750-539: A separate ophthalmology-focused institute began in earnest in the mid-1960s and culminated in President Lyndon B. Johnson signing legislation creating NEI as part of NIH. NEI was established on August 16, 1968, as the United States' first civilian governmental body focused on eye diseases, eye disorders, and vision research. NEI officially began operating on December 26, 1968, and the first meeting of

2875-405: A sharp image. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain. Focusing the image would also cause the sun's image to be focused on a few receptors, with

3000-499: A single erect image. Compound eyes are common in arthropods, annelids and some bivalved molluscs. Compound eyes in arthropods grow at their margins by the addition of new ommatidia. Apposition eyes are the most common form of eyes and are presumably the ancestral form of compound eyes. They are found in all arthropod groups, although they may have evolved more than once within this phylum. Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus ,

3125-408: A spherical lens, cornea and retina, but the vision is blurry. Heterogeneous eyes have evolved at least nine times: four or more times in gastropods , once in the copepods , once in the annelids , once in the cephalopods , and once in the chitons , which have aragonite lenses. No extant aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens

3250-415: A transparent humour that optimised colour filtering, blocked harmful radiation, improved the eye's refractive index , and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with

3375-638: A type of simple eye ( stemmata ) which usually provides only a rough image, but (as in sawfly larvae) can possess resolving powers of 4 degrees of arc, be polarization-sensitive, and capable of increasing its absolute sensitivity at night by a factor of 1,000 or more. Ocelli , some of the simplest eyes, are found in animals such as some of the snails . They have photosensitive cells but no lens or other means of projecting an image onto those cells. They can distinguish between light and dark but no more, enabling them to avoid direct sunlight . In organisms dwelling near deep-sea vents , compound eyes are adapted to see

3500-400: Is a combination of inputs from the numerous ommatidia (individual "eye units"), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarisation of light. Because the individual lenses are so small, the effects of diffraction impose

3625-412: Is a complex optical system that collects light from the surrounding environment, regulates its intensity through a diaphragm , focuses it through an adjustable assembly of lenses to form an image , converts this image into a set of electrical signals, and transmits these signals to the brain through neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of

3750-528: Is a lack of one or more of the cone subtypes that causes individuals to have deficiencies in colour vision or various kinds of colour blindness . These individuals are not blind to objects of a particular colour, but are unable to distinguish between colours that can be distinguished by people with normal vision. Humans have this trichromatic vision , while most other mammals lack cones with red sensitive pigment and therefore have poorer dichromatic colour vision. However, some animals have four spectral subtypes, e.g.

3875-412: Is a simple eye, it produces an inverted image; those images are combined in the brain to form one unified image. Because the aperture of an eyelet is larger than the facets of a compound eye, this arrangement allows vision under low light levels. Good fliers such as flies or honey bees, or prey-catching insects such as praying mantis or dragonflies , have specialised zones of ommatidia organised into

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4000-404: Is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. This would have led to a somewhat different evolutionary trajectory for the vertebrate eye than for other animal eyes. The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialise into

4125-417: Is also available. Changes in retinal blood circulation are seen with aging and exposure to air pollution, and may indicate cardiovascular diseases such as hypertension and atherosclerosis. Determining the equivalent width of arterioles and venules near the optic disc is also a widely used technique to identify cardiovascular risks. The retina translates an optical image into neural impulses starting with

4250-463: Is an eye condition that can cause vision loss and blindness in people with diabetes. NEI has supported several studies on the treatment of diabetic retinopathy, including: Glaucoma refers to a group of eye diseases that damage the optic nerve and cause vision loss and blindness. Open-angle glaucoma is the most common form of glaucoma in the United States. Most clinical trials focus on managing open-angle glaucoma by reducing intraocular pressure (IOP),

4375-537: Is called mesopic vision . At mesopic light levels, both the rods and cones are actively contributing pattern information. What contribution the rod information makes to pattern vision under these circumstances is unclear. The response of cones to various wavelengths of light is called their spectral sensitivity. In normal human vision, the spectral sensitivity of a cone falls into one of three subtypes, often called blue, green, and red, but more accurately known as short, medium, and long wavelength-sensitive cone subtypes. It

4500-542: Is considered a key factor in this. The majority of the advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true imaging would have touched off an "arms race" among all species that did not flee the photopic environment. Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye types and subtypes developed in parallel (except those of groups, such as

4625-401: Is great enough for this stage to be quickly "outgrown". This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimise the effect of eye motion while the animal moves, most such eyes have stabilising eye muscles. The ocelli of insects bear a simple lens, but their focal point usually lies behind the retina; consequently, those can not form

4750-464: Is hyperpolarised. The amount of neurotransmitter released is reduced in bright light and increases as light levels fall. The actual photopigment is bleached away in bright light and only replaced as a chemical process, so in a transition from bright light to darkness the eye can take up to thirty minutes to reach full sensitivity. When thus excited by light, the photoceptor sends a proportional response synaptically to bipolar cells which in turn signal

4875-427: Is important for entrainment of circadian rhythms and reflexive responses such as the pupillary light reflex . Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses that are sent to various visual centres of the brain through the fibres of the optic nerve . Neural signals from the rods and cones undergo processing by other neurons, whose output takes

5000-450: Is inflammation of the uvea , the middle layer of the eye between the sclera and the retina . NEI has supported several studies to examine the causes of uveitis, including: Leber congenital amaurosis is a rare inherited eye disease that impairs vision starting in infancy. NEI supported work leading to a gene therapy for one type of this disease: In December 2017, Luxturna became the first directly administered gene therapy approved in

5125-410: Is little difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures that have returned to the water—penguins and seals, for example—lose their highly curved cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strongly focusing cornea. A unique feature of most mammal eyes is the presence of eyelids which wipe

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5250-403: Is most enhanced. The choroid supplies about 75% of these nutrients to the retina and the retinal vasculature only 25%. When light strikes 11-cis-retinal (in the disks in the rods and cones), 11-cis-retinal changes to all-trans-retinal which then triggers changes in the opsins. Now, the outer segments do not regenerate the retinal back into the cis- form once it has been changed by light. Instead

5375-438: Is not direct. Since about 150 million receptors and only 1 million optic nerve fibres exist, convergence and thus mixing of signals must occur. Moreover, the horizontal action of the horizontal and amacrine cells can allow one area of the retina to control another (e.g. one stimulus inhibiting another). This inhibition is key to lessening the sum of messages sent to the higher regions of the brain. In some lower vertebrates (e.g.

5500-781: Is part of the NIH Intramural Research Program , which conducts eye and vision research on the NIH campus in Bethesda, Maryland. In support of its extramural and intramural activities, the NEI has established several offices and research initiatives to facilitate oversight and collaboration in specific areas of emphasis. NEI-supported research has contributed important knowledge about the cause, progression, and treatment of many eye diseases. Some notable examples are described below. AMD typically happens when aging damages

5625-423: Is partly transparent, and the accompanying glial cells have been shown to act as fibre-optic channels to transport photons directly to the photoreceptors, light scattering does occur. Some vertebrates, including humans, have an area of the central retina adapted for high-acuity vision. This area, termed the fovea centralis , is avascular (does not have blood vessels), and has minimal neural tissue in front of

5750-528: Is that it combines two benefits - the maintenance of the photoreceptors mentioned above, and the reduction in light intensity necessary to avoid blinding the photoreceptors, which are based on the extremely sensitive eyes of the ancestors of modern hagfish (fish that live in very deep, dark water). A recent study on the evolutionary purpose for the inverted retina structure from the APS (American Physical Society) says that "The directional of glial cells helps increase

5875-472: Is that photoreceptors are G-protein coupled receptors but TRP are ion channels . The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable. The most basic form, seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with

6000-778: Is to educate health care providers, scientists, policymakers, and the public about advances in vision research and their impact on health and quality of life. This effort is led by NEI's National Eye Health Education Program. NEI created the National Eye Health Education Program to educate professionals and the public about the importance of eye health. The program partners with more than 60 national organizations representing health professionals, educators, and patients in accomplishing this mission. It also oversees public and professional education programs on diabetic eye disease, glaucoma, vision rehabilitation, special population outreach, and vision and aging—with

6125-440: The copepod Pontella has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilia , has two lenses in each eye, arranged like those in a telescope. Such arrangements are rare and poorly understood, but represent an alternative construction. Multiple lenses are seen in some hunters such as eagles and jumping spiders, which have

6250-467: The cornea caused by herpes infection of the eye. NEI-funded research led to a breakthrough in treatment for this condition: Optic nerve diseases, like optic neuropathy and optic neuritis , can damage the connection between the eye and the visual processing centers of the brain and cause vision loss. NEI has supported studies on the treatment of optic nerve disease, including: Retinopathy of prematurity happens when abnormal blood vessels grow in

6375-420: The incident light , while those to one side reflect it. There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp, Dioptromysis paucispinosa . The shrimp has an eye of

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6500-595: The infra-red light produced by the hot vents, allowing the creatures to avoid being boiled alive. There are ten different eye layouts. Eye types can be categorised into "simple eyes", with one concave photoreceptive surface, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface. "Simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving

6625-584: The macula . It is a leading cause of vision loss for older adults. It can blur the sharp central vision needed to read, see faces, and do close-up work. NEI has supported several studies investigating treatments for AMD, including: Although AREDS2 found no overall additional benefits, it did show that two groups of participants had improved results: participants who took the AREDS formulation with no beta-carotene and participants with very low initial levels of lutein and zeaxanthin in their diets. Diabetic retinopathy

6750-408: The ophthalmic artery bifurcates and supplies the retina via two distinct vascular networks: the choroidal network, which supplies the choroid and the outer retina, and the retinal network, which supplies the retina's inner layer. Although the inverted retina of vertebrates appears counter-intuitive, it is necessary for the proper functioning of the retina. The photoreceptor layer must be embedded in

6875-425: The outer plexiform layer and the inner plexiform layer . In the outer neuropil layer, the rods and cones connect to the vertically running bipolar cells , and the horizontally oriented horizontal cells connect to ganglion cells. The central retina predominantly contains cones, while the peripheral retina predominantly contains rods. In total, the retina has about seven million cones and a hundred million rods. At

7000-412: The photosensitive ganglion cells ; and transmission along the optic nerve. At each synaptic stage, horizontal and amacrine cells also are laterally connected. The optic nerve is a central tract of many axons of ganglion cells connecting primarily to the lateral geniculate body , a visual relay station in the diencephalon (the rear of the forebrain). It also projects to the superior colliculus ,

7125-787: The pigeon ), control of messages is "centrifugal" – that is, one layer can control another, or higher regions of the brain can drive the retinal nerve cells, but in primates, this does not occur. Using optical coherence tomography (OCT), 18 layers can be identified in the retina. The layers and anatomical correlation are: From innermost to outermost, the layers identifiable by OCT are as follows: on OCT anatomical boundaries? references (unclear if it can be observed on OCT) b) Müller cell nuclei (obliquely orientated fibres; not present in mid-peripheral or peripheral retina) Poorly distinguishable from RPE. Previously: "cone outer segment tips line" (COST) homogenous region of variable reflectivity Retinal development begins with

7250-480: The pretectal area to control the pupillary light reflex . Complex eyes distinguish shapes and colours . The visual fields of many organisms, especially predators, involve large areas of binocular vision for depth perception . In other organisms, particularly prey animals, eyes are located to maximise the field of view, such as in rabbits and horses , which have monocular vision . The first proto-eyes evolved among animals 600  million years ago about

7375-403: The receptive field of the cell. The receptive fields of retinal ganglion cells comprise a central, approximately circular area, where light has one effect on the firing of the cell, and an annular surround, where light has the opposite effect. In ON cells, an increment in light intensity in the centre of the receptive field causes the firing rate to increase. In OFF cells, it makes it decrease. In

7500-425: The retinal ganglion cells . The photoreceptors are also cross-linked by horizontal cells and amacrine cells , which modify the synaptic signal before it reaches the ganglion cells, the neural signals being intermixed and combined. Of the retina's nerve cells, only the retinal ganglion cells and few amacrine cells create action potentials . In the retinal ganglion cells there are two types of response, depending on

7625-422: The rod cells (for low-light contrasts) in the retina detect and convert light into neural signals which are transmitted to the brain via the optic nerve to produce vision. Such eyes are typically spheroid, filled with the transparent gel-like vitreous humour , possess a focusing lens , and often an iris . Muscles around the iris change the size of the pupil , regulating the amount of light that enters

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7750-431: The suprachiasmatic nucleus , and the nucleus of the optic tract . It passes through the other layers, creating the optic disc in primates. Additional structures, not directly associated with vision, are found as outgrowths of the retina in some vertebrate groups. In birds , the pecten is a vascular structure of complex shape that projects from the retina into the vitreous humour ; it supplies oxygen and nutrients to

7875-501: The 1950s and early 1960s, producing results despite small budgets. One notable example was the study that identified the cause of retrolental fibroplasia (now known as retinopathy of prematurity , the leading cause of blindness among children at the time. Despite this progress, some prominent members of the vision research community asserted that too many important proposals for ophthalmic research were not granted funding. They also emphasized that ophthalmology could stand on its own as

8000-536: The Audacious Goals Initiative for Regenerative Medicine. The initiative is a strategic research effort to replace cells of the retina that have been damaged by disease or injury and to restore their connections to the visual centers of the brain. Success will mean new approaches to prevent and even reverse vision loss caused by diseases such as AMD and glaucoma . Directors dating to 1970 In November 2020, Michael F. Chiang , began serving as

8125-523: The N-T axis is coordinated by expression of the forkhead transcription factors FOXD1 and FOXG1 . Additional gradients are formed within the retina. This spatial distribution may aid in proper targeting of RGC axons that function to establish the retinotopic map. The retina is stratified into distinct layers, each containing specific cell types or cellular compartments that have metabolisms with different nutritional requirements. To satisfy these requirements,

8250-607: The NEI Strategic Plan Vision for the Future 2021-2025 outlines seven cross-cutting areas of emphasis: genetics, neuroscience, immunology, regenerative medicine, data science, quality of life, and public health and health disparities. These areas emphasize the methodological expertise required to address challenges across the entire visual system and facilitate translation of promising findings into clinical care and population health. NEI's Intramural Research Program

8375-635: The National Advisory Eye Council occurred on April 3, 1969. The first director of NEI, Carl Kupfer, was appointed on January 11, 1970.   From 1970 to Kupfer's retirement in 2000, NEI's budget grew from $ 24 million to over $ 500 million.[3] Kupfer expanded NEI's vision research program to focus not only on the eyes but on the entire visual system , including visual processing in the brain.   In June 2001, Paul A. Sieving , joined NEI as its second director and served until July 2019. Under Sieving's directorship, NEI established

8500-560: The Omnibus Medical Research Act. This bill marked the beginning of vision research at the federal level. Organizing, structuring, and separating vision and neurological research was a challenge at National Institute of Neurological Disease and Blindness. In its early years, securing funding was difficult. The institute established an Ophthalmology Branch, which served primarily as an ophthalmic consultation service for NIH. Ophthalmic research grew slowly throughout

8625-400: The United States and worldwide. The NEI extramural research program is organized by anatomy and disease around core areas: retina; cornea; lens and cataract; glaucoma and optic neuropathy; strabismus, amblyopia, and visual processing; and vision rehabilitation. These core areas reflect clinical divisions of most ophthalmology and optometry departments. In addition to these core program areas,

8750-435: The United States that targets a disease caused by mutations in a specific gene. It was approved for the treatment of patients with confirmed biallelic RPE65 mutation-associated retinal dystrophy that leads to vision loss and may cause complete blindness in certain patients. NEI has invested in the development of technologies to support diagnosis and management. A few examples of this investment include: Part of NEI's mission

8875-488: The absorption of stray light falling on the pecten. This is considered to enhance metabolic rate of the pecten, thereby exporting more nutritive molecules to meet the stringent energy requirements of the retina during long periods of exposure to light. The bifurcations and other physical characteristics of the inner retinal vascular network are known to vary among individuals, and these individual variances have been used for biometric identification and for early detection of

9000-454: The brain, the retina is isolated from the vascular system by the blood–brain barrier . The retina is the part of the body with the greatest continuous energy demand. The vertebrate retina is inverted in the sense that the light-sensing cells are in the back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the photosensitive sections of the rods and cones. The ganglion cells, whose axons form

9125-471: The brain. Eyes with resolving power have come in ten fundamentally different forms, classified into compound eyes and non-compound eyes. Compound eyes are made up of multiple small visual units, and are common on insects and crustaceans . Non-compound eyes have a single lens and focus light onto the retina to form a single image. This type of eye is common in mammals, including humans. The simplest eyes are pit eyes. They are eye-spots which may be set into

9250-399: The cells of the dilator muscle. The vitreous is the transparent, colourless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye. It is produced by certain retinal cells. It is of rather similar composition to the cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as

9375-411: The centre of the macula is the foveal pit where the cones are narrow and long, and arranged in a hexagonal mosaic , the most dense, in contradistinction to the much fatter cones located more peripherally in the retina. At the foveal pit, the other retinal layers are displaced, before building up along the foveal slope until the rim of the fovea, or parafovea , is reached, which is the thickest portion of

9500-483: The clarity of human vision. But we also noticed something rather curious: the colours that best passed through the glial cells were green to red, which the eye needs most for daytime vision. The eye usually receives too much blue—and thus has fewer blue-sensitive cones. Further computer simulations showed that green and red are concentrated five to ten times more by the glial cells, and into their respective cones, than blue light. Instead, excess blue light gets scattered to

9625-422: The correspondence between X and Y cells (in the cat retina) and P and M cells (in the primate retina) is not as simple as it once seemed. In the transfer of visual signals to the brain, the visual pathway , the retina is vertically divided in two, a temporal (nearer to the temple) half and a nasal (nearer to the nose) half. The axons from the nasal half cross the brain at the optic chiasma to join with axons from

9750-399: The directionality of light by the shadow cast by its opaque body. The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes

9875-588: The edge of its shell. It detects moving objects as they pass successive lenses. There is at least one vertebrate, the spookfish , whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of guanine crystals . A compound eye may consist of thousands of individual photoreceptor units or ommatidia ( ommatidium , singular). The image perceived

10000-532: The establishment of the eye fields mediated by the SHH and SIX3 proteins, with subsequent development of the optic vesicles regulated by the PAX6 and LHX2 proteins. The role of Pax6 in eye development was elegantly demonstrated by Walter Gehring and colleagues, who showed that ectopic expression of Pax6 can lead to eye formation on Drosophila antennae, wings, and legs. The optic vesicle gives rise to three structures:

10125-563: The eye and reducing aberrations when there is enough light. The eyes of most cephalopods , fish , amphibians and snakes have fixed lens shapes, and focusing is achieved by telescoping the lens in a similar manner to that of a camera . The compound eyes of the arthropods are composed of many simple facets which, depending on anatomical detail, may give either a single pixelated image or multiple images per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors arranged hexagonally, which can give

10250-412: The eye and spread tears across the cornea to prevent dehydration. These eyelids are also supplemented by the presence of eyelashes , multiple rows of highly innervated and sensitive hairs which grow from the eyelid margins to protect the eye from fine particles and small irritants such as insects. An alternative to a lens is to line the inside of the eye with "mirrors", and reflect the image to focus at

10375-407: The eye, and may also aid in vision. Reptiles have a similar, but much simpler, structure. In adult humans, the entire retina is about 72% of a sphere about 22 mm in diameter. The entire retina contains about 7 million cones and 75 to 150 million rods. The optic disc, a part of the retina sometimes called "the blind spot" because it lacks photoreceptors, is located at the optic papilla , where

10500-400: The eye. Photoreception is phylogenetically very old, with various theories of phylogenesis. The common origin ( monophyly ) of all animal eyes is now widely accepted as fact. This is based upon the shared genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 650-600 million years ago, and the PAX6 gene

10625-403: The field or lab," and "Science in your future." One winner is selected in each category, each receiving a prize of $ 2,000 USD. Eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system . In higher organisms, the eye

10750-499: The form of action potentials in retinal ganglion cells whose axons form the optic nerve. In vertebrate embryonic development , the retina and the optic nerve originate as outgrowths of the developing brain, specifically the embryonic diencephalon ; thus, the retina is considered part of the central nervous system (CNS) and is actually brain tissue. It is the only part of the CNS that can be visualized noninvasively . Like most of

10875-481: The geometry of cephalopod and most vertebrate eyes creates the impression that the vertebrate eye evolved from an imaging cephalopod eye , but this is not the case, as the reversed roles of their respective ciliary and rhabdomeric opsin classes and different lens crystallins show. The very earliest "eyes", called eye-spots, were simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots evolved, physically similar to

11000-449: The horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point. (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.) Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has

11125-425: The hyalocytes of Balazs of the surface of the vitreous, which reprocess the hyaluronic acid ), no blood vessels, and 98–99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibres with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds

11250-668: The importance of early detection and timely treatment of eye disease and the benefits of vision rehabilitation. The program also aims to increase awareness among health professionals and the public of science-based health information that can be applied to preserving sight and preventing blindness. In 2022, the NEI created the Eye on the Future Teen Video Contest to foster the next generation of American scientists. The NEI awards American youth who create educational videos in three categories: "Science in your world," "Science in

11375-424: The lens tissue is corrected with inhomogeneous lens material (see Luneburg lens ), or with an aspheric shape. Flattening the lens has a disadvantage; the quality of vision is diminished away from the main line of focus. Thus, animals that have evolved with a wide field-of-view often have eyes that make use of an inhomogeneous lens. As mentioned above, a refractive cornea is only useful out of water. In water, there

11500-480: The lenses of their eyes. They differ in this from most other arthropods, which have soft eyes. The number of lenses in such an eye varied widely; some trilobites had only one while others had thousands of lenses per eye. In contrast to compound eyes, simple eyes have a single lens. Jumping spiders have one pair of large simple eyes with a narrow field of view , augmented by an array of smaller eyes for peripheral vision . Some insect larvae , like caterpillars , have

11625-511: The neural retina, the retinal pigmented epithelium, and the optic stalk. The neural retina contains the retinal progenitor cells (RPCs) that give rise to the seven cell types of the retina. Differentiation begins with the retinal ganglion cells and concludes with production of the Muller glia. Although each cell type differentiates from the RPCs in a sequential order, there is considerable overlap in

11750-399: The only known modifiable risk factor for glaucoma. NEI has supported several studies, including: Amblyopia is a type of visual impairment that occurs when the brain does not recognize visual signals from one eye and favors the other eye. NEI has supported research into effective treatment for amblyopia, including: Corneal stromal keratitis or herpetic simplex keratitis is inflammation of

11875-521: The onset of disease. The mapping of vascular bifurcations is one of the basic steps in biometric identification. Results of such analyses of retinal blood vessel structure can be evaluated against the ground truth data of vascular bifurcations of retinal fundus images that are obtained from the DRIVE dataset. In addition, the classes of vessels of the DRIVE dataset have also been identified, and an automated method for accurate extraction of these bifurcations

12000-445: The optic nerve are devoted to the fovea. The resolution limit of the fovea has been determined to be around 10,000 points. The information capacity is estimated at 500,000 bits per second (for more information on bits, see information theory ) without colour or around 600,000 bits per second including colour. When the retina sends neural impulses representing an image to the brain, it spatially encodes (compresses) those impulses to fit

12125-421: The optic nerve, are at the front of the retina; therefore, the optic nerve must cross through the retina en route to the brain. No photoreceptors are in this region, giving rise to the blind spot . In contrast, in the cephalopod retina, the photoreceptors are in front, with processing neurons and capillaries behind them. Because of this, cephalopods do not have a blind spot. Although the overlying neural tissue

12250-478: The optic-nerve fibres leave the eye. It appears as an oval white area of 3 mm . Temporal (in the direction of the temples) to this disc is the macula , at whose centre is the fovea , a pit that is responsible for sharp central vision, but is actually less sensitive to light because of its lack of rods. Human and non-human primates possess one fovea, as opposed to certain bird species, such as hawks, that are bifoviate, and dogs and cats, that possess no fovea, but

12375-459: The parabolic superposition compound eye type, seen in arthropods such as mayflies , the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp , prawns , crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses. This eye type functions by refracting light, then using

12500-747: The patterned excitation of the colour-sensitive pigments of its rods and cones, the retina's photoreceptor cells . The excitation is processed by the neural system and various parts of the brain working in parallel to form a representation of the external environment in the brain. The cones respond to bright light and mediate high-resolution colour vision during daylight illumination (also called photopic vision ). The rod responses are saturated at daylight levels and do not contribute to pattern vision. However, rods do respond to dim light and mediate lower-resolution, monochromatic vision under very low levels of illumination (called scotopic vision ). The illumination in most office settings falls between these two levels and

12625-499: The photoreceptors, thereby minimizing light scattering. The cephalopods have a non-inverted retina, which is comparable in resolving power to the eyes of many vertebrates. Squid eyes do not have an analog of the vertebrate retinal pigment epithelium (RPE). Although their photoreceptors contain a protein, retinochrome, that recycles retinal and replicates one of the functions of the vertebrate RPE, cephalopod photoreceptors are likely not maintained as well as in vertebrates, and that as

12750-461: The possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity. This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above). Some marine organisms bear more than one lens; for instance

12875-438: The receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the light source. Through gradual change, the eye-spots of species living in well-lit environments depressed into a shallow "cup" shape. The ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify

13000-514: The refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialised retina. The resulting eye is a mixture of a simple eye within a compound eye. Another version is a compound eye often referred to as "pseudofaceted", as seen in Scutigera . This type of eye consists of

13125-464: The resting state the cell is depolarised. The photon causes the retinal bound to the receptor protein to isomerise to trans-retinal . This causes the receptor to activate multiple G-proteins . This in turn causes the Ga-subunit of the protein to activate a phosphodiesterase (PDE6), which degrades cGMP, resulting in the closing of Na+ cyclic nucleotide-gated ion channels (CNGs). Thus the cell

13250-506: The retina and cause vision loss and blindness in babies who are premature or who weigh less than 3 pounds at birth. NEI has supported studies investigating the treatment and progression of retinopathy of prematurity, including: Retinitis pigmentosa refers to a group of genetic eye diseases that cause cells in the retina to degenerate, leading to impaired night vision and loss of peripheral vision . NEI has supported research into therapies that slow disease progression, including: Uveitis

13375-419: 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 . The neural retina consists of several layers of neurons interconnected by synapses and is supported by an outer layer of pigmented epithelial cells. The primary light-sensing cells in

13500-414: The retina are the photoreceptor cells , which are of two types: rods and cones . Rods function mainly in dim light and provide monochromatic vision. Cones function in well-lit conditions and are responsible for the perception of colour through the use of a range of opsins , as well as high-acuity vision used for tasks such as reading. A third type of light-sensing cell, the photosensitive ganglion cell ,

13625-450: The retina. The macula has a yellow pigmentation, from screening pigments, and is known as the macula lutea. The area directly surrounding the fovea has the highest density of rods converging on single bipolar cells. Since its cones have a much lesser convergence of signals, the fovea allows for the sharpest vision the eye can attain. Though the rod and cones are a mosaic of sorts, transmission from receptors, to bipolars, to ganglion cells

13750-514: The retinal is pumped out to the surrounding RPE where it is regenerated and transported back into the outer segments of the photoreceptors. This recycling function of the RPE protects the photoreceptors against photo-oxidative damage and allows the photoreceptor cells to have decades-long useful lives. The bird retina is devoid of blood vessels, perhaps to give unobscured passage of light for forming images, thus giving better resolution. It is, therefore,

13875-490: The retinal pigment epithelium (RPE), which performs at least seven vital functions, one of the most obvious being to supply oxygen and other necessary nutrients needed for the photoreceptors to function. The energy requirements of the retina are even greater than that of the brain. This is due to the additional energy needed to continuously renew the photoreceptor outer segments, of which 10% are shed daily. Energy demands are greatest during dark adaptation when its sensitivity

14000-500: The rods and cones. Light is absorbed by the retinal pigment epithelium or the choroid (both of which are opaque). The white blood cells in the capillaries in front of the photoreceptors can be perceived as tiny bright moving dots when looking into blue light. This is known as the blue field entoptic phenomenon (or Scheerer's phenomenon). Between the ganglion-cell layer and the rods and cones are two layers of neuropils , where synaptic contacts are made. The neuropil layers are

14125-416: The same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This type of compound eye, for which a minimal size exists below which effective superposition cannot occur, is normally found in nocturnal insects, because it can create images up to 1000 times brighter than equivalent apposition eyes, though at the cost of reduced resolution. In

14250-404: The source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes. However, the ancestors of modern hagfish , thought to be the protovertebrate, were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it

14375-418: The surrounding rods. This optimization is such that color vision during the day is enhanced, while night-time vision suffers very little". The vertebrate retina has 10 distinct layers. From closest to farthest from the vitreous body: These layers can be grouped into four main processing stages—photoreception; transmission to bipolar cells ; transmission to ganglion cells , which also contain photoreceptors,

14500-622: The surroundings are light or dark , which is sufficient for the entrainment of circadian rhythms . These are not considered eyes because they lack enough structure to be considered an organ, and do not produce an image. Every technological method of capturing an optical image that humans commonly use occurs in nature, with the exception of zoom and Fresnel lenses . Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates , cephalopods , annelids , crustaceans and Cubozoa . Pit eyes, also known as stemmata , are eye-spots which may be set into

14625-450: The temporal half of the other eye before passing into the lateral geniculate body . Although there are more than 130 million retinal receptors, there are only approximately 1.2 million fibres (axons) in the optic nerve. So, a large amount of pre-processing is performed within the retina. The fovea produces the most accurate information. Despite occupying about 0.01% of the visual field (less than 2° of visual angle ), about 10% of axons in

14750-518: The third director of NEI. Chiang, a pediatric ophthalmologist , conducts research on the interface of biomedical informatics and clinical ophthalmology in areas such as retinopathy of prematurity , telehealth , artificial intelligence , electronic health records , data science , and genotype – phenotype correlation. NEI supports extramural vision research through about 2,100 research grants and training awards to scientists at more than 150 medical centers, universities, and other institutions across

14875-462: The time of the Cambrian explosion . The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35 main phyla . In most vertebrates and some molluscs , the eye allows light to enter and project onto a light-sensitive layer of cells known as the retina . The cone cells (for colour) and

15000-430: The timing of when individual cell types differentiate. The cues that determine a RPC daughter cell fate are coded by multiple transcription factor families including the bHLH and homeodomain factors. In addition to guiding cell fate determination, cues exist in the retina to determine the dorsal-ventral (D-V) and nasal-temporal (N-T) axes. The D-V axis is established by a ventral to dorsal gradient of VAX2 , whereas

15125-407: The transparent crystallin protein. Retina The retina (from Latin rete  'net'; pl.   retinae or retinas ) 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

15250-479: The trout adds an ultraviolet subgroup to short, medium, and long subtypes that are similar to humans. Some fish are sensitive to the polarization of light as well. In the photoreceptors, exposure to light hyperpolarizes the membrane in a series of graded shifts. The outer cell segment contains a photopigment . Inside the cell the normal levels of cyclic guanosine monophosphate (cGMP) keep the Na+ channel open, and thus in

15375-436: The unique ribbon synapse . The optic nerve carries the ganglion-cell axons to the brain, and the blood vessels that supply the retina. The ganglion cells lie innermost in the eye while the photoreceptive cells lie beyond. Because of this counter-intuitive arrangement, light must first pass through and around the ganglion cells and through the thickness of the retina, (including its capillary vessels, not shown) before reaching

15500-469: The vertebrates, that were only forced into the photopic environment at a late stage). Eyes in various animals show adaptation to their requirements. For example, the eye of a bird of prey has much greater visual acuity than a human eye , and in some cases can detect ultraviolet radiation. The different forms of eye in, for example, vertebrates and molluscs are examples of parallel evolution , despite their distant common ancestry. Phenotypic convergence of

15625-568: The work of several Nobel Prize recipients, including Roger Y. Tsien (2008); Peter Agre (2003); David H. Hubel (1981); and Torsten Wiesel (1981). Before 1968, vision research at NIH was funded and overseen by the National Institute of Neurological Disease and Blindness (now known as the National Institute of Neurological Disorders and Stroke ), which was established in 1950, after President Harry S. Truman signed

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