"and a nontransparent layer may split forward from the lens: a separate cornea and iris. (These may happen before or after crystal deposition, or not at all.) Separation of the forward layer again forms a humour, the aqueous humour. This increases refractive power and again eases circulatory problems. Formation of a nontransparent ring allows more blood vessels, more circulation, and larger eye sizes. This flap around the perimeter of the lens also masks optical imperfections, which are more common at lens edges. The need to mask lens imperfections gradually increases with lens curvature and power, overall lens and eye size,"
"Lens (anatomy) The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known as accommodation (see also ). Accommodation is similar to the focusing of a photographic camera via movement of its lenses. The lens is also known"
"when objects projected directly onto the fovea are the sharpest, while those further out in the periphery of the retina become steadily less focused. This is due to the distribution of cones and rods throughout the retina. When we view an image, light passes through the cornea, and through the pupil, which is controlled by the iris. It then passes through the lens and is projected onto the retina at the back of the eye. In the middle of the retina is the fovea, which contains a high concentration of cones. Cones are responsible for colour vision and have high"
"is located behind the lens and in front of the optic nerve. This chamber is filled with a thick, clear gel-like substance called the vitreous humor (also vitreous body). The humor plays a crucial role in supporting the posterior side of the lens. The vitreous fluid, along with supporting the lens, also functions in maintaining the shape of the entire vitreous chamber and posterior cavity. It is imperative that the eye remains the proper shape to ensure that the light passing through the lens and the fluid can focus properly on the retina. The composition of the fluid is 99%"
"is maintained by the Na/K-ATPase] pumps located in the equatorially positioned cells of the lens epithelium. Glucose is the primary energy source for the lens. As mature lens fibers do not have mitochondria, approximately 80% of the glucose is metabolized via anaerobic metabolism. The remaining fraction of glucose is shunted primarily down the pentose phosphate pathway. The lack of aerobic respiration means that the lens consumes very little oxygen as well. Lens (anatomy) The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens,"
"as the ""aquula"" (Latin, ""a little stream"", dim. of ""aqua"", ""water"") or ""crystalline lens"". The lens is part of the anterior segment of the human eye. In front of the lens is the iris, which regulates the amount of light entering into the eye. The lens is suspended in place by the suspensory ligament of the lens, a ring of fibrous tissue that attaches to the lens at its equator and connects it to the ciliary body. Posterior to the lens is the vitreous body, which, along with the aqueous humor on the anterior surface, bathes the lens. The lens"
"to the medial aspect of the eye and its contraction adducts the eye. The medial rectus is innervated by motor neurons in the oculomotor nucleus and nerve. The refractive index of the eye’s lens system allows the eye to produce sharply focused images. For example, geometrical optics show that as a distant object is brought closer to the eye, the focus of the object becomes blurrier in the plane behind the retina; however, as a result of the increase in the refractive power of the eye, this image becomes clear. The refractive power mainly resides in the cornea, but the"
"in two areas: the anterior chamber between the cornea and the iris, and the posterior chamber between the iris and the lens. The lens is suspended to the ciliary body by the suspensory ligament (Zonule of Zinn), made up of hundreds of fine transparent fibers which transmit muscular forces to change the shape of the lens for accommodation (focusing). The vitreous body is a clear substance composed of water and proteins, which give it a jelly-like and sticky composition. The approximate field of view of an individual human eye (measured from the fixation point, i.e., the point at which one's"
"Focusing screen A focusing screen is a flat translucent material, either a ground glass or Fresnel lens, found in a system camera that allows the user of the camera to preview the framed image in a viewfinder. Often, focusing screens are available in variants with different etched markings for various purposes. For instance, ""overall matte"" focusing screens with no etchings are a popular choice for astrophotography and other low-light situations. The history of the focusing screen is almost as long as the history of the camera. Some primitive cameras consisted of a box with a board holding the lens in"
"this affects the focusing of the eye. Most animals' eyes are adapted to either underwater or air vision, and do not focus properly when in the other environment. The crystalline lenses of fishes' eyes are extremely convex, almost spherical, and their refractive indices are the highest of all the animals. These properties enable proper focusing of the light rays and in turn proper image formation on the retina. This convex lens gives the name to the fisheye lens in photography. By wearing a flat diving mask, humans can see clearly underwater. The scuba mask's flat window separates the eyes from"
"fact, visible only because they do not remain perfectly fixed within the eye. Although the blood vessels of the eye also obstruct light, they are invisible under normal circumstances because they are fixed in location relative to the retina, and the brain ""tunes out"" stabilized images due to neural adaptation. This stabilization is often interrupted by floaters, especially when they tend to remain visible. Floaters are particularly noticeable when looking at a blank surface or an open monochromatic space, such as blue sky. Despite the name ""floaters"", many of these specks have a tendency to sink toward the bottom of"
"It requires not only the muscles of the eye – the muscles of orbit and the ciliary muscles – to be able to focus on a particular object through contraction and relaxation, but other parts of the retina such as the fovea to project a clear image on the retina. The muscles that initiate movement start to strengthen from birth to 2 months, at which point infants have control of their eye. However, images still appear unclear at two months due to other components of the visual system like the fovea and retina and the brain circuitry that are still"
"of degenerative diseases including Parkinson's disease and multiple sclerosis. Fixation (visual) Fixation or visual fixation is the maintaining of the visual gaze on a single location. An animal can exhibit visual fixation if they possess a fovea in the anatomy of their eye. The fovea is typically located at the center of the retina and is the point of clearest vision. The species in which fixational eye movement has been found thus far include humans, primates, cats, rabbits, turtles, salamanders, and owls. Regular eye movement alternates between saccades and visual fixations, the notable exception being in smooth pursuit, controlled by"
"the conjunctiva and cornea that together with lacrimal gland comprise much of the lacrimal functional unit (LFU). Viewed collectively, the LFU is the primary source of lacritin in the body, and the eye the main target. Dry eye is the most common eye disease, affecting 5 - 6% of the population. Prevalence rises to 6 - 9.8% in postmenopausal women, and as high as 34% in the elderly. Tears lubricate the lid and are important for the refraction of light. Tears also promote epithelial health. Only a small fraction of the estimated 1543 proteins in tears are differentially deficient or"
"non-aiming eye should be kept open. The non-aiming eye can be blocked from seeing distractions by mounting a semi-transparent occluder to the diopter. Even for the maximum precision, there should still be a significant area of white visible around the bullseye and between the front and rear sight ring (if a front ring is being used). Since the best key to determining center is the amount of light passing through the apertures, a narrow, dim ring of light can actually be more difficult to work with than a larger, brighter ring. The precise sizes of the employed components are quite"
"of too much aqueous humor, or reabsorption that occurs too slowly, can lead to increases in the pressure within the eye. Pars plicata The pars plicata (Latin: folded portion) is the folded and most anterior portion of the ciliary body of an eye. The ciliary body is a part of the uvea, one of the three layers that comprise the eye. The pars plicata is located anterior to the pars plana portion of the ciliary body, and posterior to the iris. The lens zonules that are used to control accommodation are attached to the pars plicata. The pars plicata is"
"eyes. Three pairs of eyes positioned along the sides of the cephalothorax (called the secondary eyes) have a combined field-of-view of almost 360° and serve primarily as movement detectors. A pair of forward-facing anterior median eyes (called the principal eyes) are adapted for colour vision and high spatial acuity. The main eyes focus accurately on an object at distances from approximately to infinity, and in practice can see up to about . Like all jumping spiders, ""Portia""s can take in only a small visual field at one time, as the most acute part of a main eye can see all"
"onto the front of the Step Up/Shade. Original Lensbaby<br> The Original Lensbaby is a flexible camera lens that creates an image that has an area of sharp focus surrounded by graduated blur. The lens is the initial springboard for the products to follow, the initial principal of shifting in the in-focus area by bending the flexible lens tube in any direction. Specs of the Original Lensbaby 2.0<br> The 2.0 is the second generation of Lensbaby lenses, it improved on the initial design of the Original Lensbaby by adding additional apertures and improvement in the optical glass doublet. 'Specs of the"
"directly at an object but the eyes drift off their target, the fixation reflex keeps the eyes focused on the original object, albeit moving itself Fixation reflex The fixation reflex is that concerned with attracting the eye on a peripheral object. For example, when a light shines in the periphery, the eyes shift gaze on it. It is controlled by the occipital lobe of the cerebral cortex, corroborated by three main tests: Older research declares that a motor pathway from the occipital cortex to the brainstem motor neurons was via the superior colliculi. This is the case in lower animals,"
"other vertebrates. The outer layer of the eye consists of the transparent cornea at the front, and two layers of sclera — a tough white collagen fibre layer which surrounds the rest of the eye and supports and protects the eye as a whole. The eye is divided internally by the lens into two main segments: the anterior segment and the posterior segment. The anterior chamber is filled with a watery fluid called the aqueous humour, and the posterior chamber contains the vitreous humour, a clear jelly-like substance. The lens is a transparent convex or 'lens' shaped body with a"
"main phyla. In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of"
"Fixation (visual) Fixation or visual fixation is the maintaining of the visual gaze on a single location. An animal can exhibit visual fixation if they possess a fovea in the anatomy of their eye. The fovea is typically located at the center of the retina and is the point of clearest vision. The species in which fixational eye movement has been found thus far include humans, primates, cats, rabbits, turtles, salamanders, and owls. Regular eye movement alternates between saccades and visual fixations, the notable exception being in smooth pursuit, controlled by a different neural substrate that appears to have developed"
"object to another. Understanding of the visual scene becomes more efficient because these attention shifts guide the eyes towards relevant objects as opposed to objects that may not be as important. The lateral intraparietal cortex (LIP) is an area that is believed to be primarily responsible for keeping an image fluid and undistorted during a saccade (visual/spatial constancy). Past work has shown that the LIP stores information of objects before the saccade (presaccadic), which is then followed by a shift in the receptive fields of the brain cells of this area to compensate for the displacement of the retina during"
"of the cone mosaic, and the fovea is the area of the eye with the highest sensitivity to fine details. Cones in the central fovea express pigments that are sensitive to green and red light. These cones are the 'midget' pathways that also underpin high acuity functions of the fovea. The fovea is employed for accurate vision in the direction where it is pointed. It comprises less than 1% of retinal size but takes up over 50% of the visual cortex in the brain. The fovea sees only the central two degrees of the visual field, (approximately twice the width"
"μm) in thickness near its center. The posterior chamber constitutes the remaining five-sixths; its diameter is typically about 24 mm. The cornea and sclera are connected by an area termed the limbus. The iris is the pigmented circular structure concentrically surrounding the center of the eye, the pupil, which appears to be black. The size of the pupil, which controls the amount of light entering the eye, is adjusted by the iris' dilator and sphincter muscles. Light energy enters the eye through the cornea, through the pupil and then through the lens. The lens shape is changed for near focus"
"focal point always lies behind the retina; consequently they can never form 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 the possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity."
"fovea area which gives acute vision. In the acute zone the eye is flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. 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 the refracting superposition type, in the rear behind this"
"Fovea centralis The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina. The fovea is responsible for sharp central vision (also called foveal vision), which is necessary in humans for activities where visual detail is of primary importance, such as reading and driving. The fovea is surrounded by the ""parafovea"" belt, and the ""perifovea"" outer region. The parafovea is the intermediate belt, where the ganglion cell layer is composed of more than five rows of cells, as well as the highest"
"Fixation reflex The fixation reflex is that concerned with attracting the eye on a peripheral object. For example, when a light shines in the periphery, the eyes shift gaze on it. It is controlled by the occipital lobe of the cerebral cortex, corroborated by three main tests: Older research declares that a motor pathway from the occipital cortex to the brainstem motor neurons was via the superior colliculi. This is the case in lower animals, but in humans, the theory that eye-muscle nuclei aside from the superior colliculi of the midbrain is now generally held. When an object is focused"
"these, primarily, PAX6, considered the master regulator gene of this organ. Other effectors of proper lens development include the Wnt signaling components BCL9 and Pygo2. In many aquatic vertebrates, the lens is considerably thicker, almost spherical, to increase the refraction. This difference compensates for the smaller angle of refraction between the eye's cornea and the watery medium, as they have similar refractive indices. Even among terrestrial animals, however, the lens of primates such as humans is unusually flat. In reptiles and birds, the ciliary body touches the lens with a number of pads on its inner surface, in addition to"
"the camera Campus is holding in the center image, although it is zoomed in quite far. Campus initially points the camera outside the window (this is the only moment where the outside is visible in detail: a neighbor's brick window) then continues to pan around the room. Because the camera is zoomed in, the image moves jerkily. In vision, the fovea is the center of the retina. It has the highest concentration of cones and no rods. Significantly, it produces the highest visual acuity and serves as the center of fixation, only registering a small part of the visual field."
"focal length of an early lobopod with lens-containing simple eyes focused the image ""behind"" the retina, so while no part of the image could be brought into focus, the intensity of light allowed the organism to see in deeper (and therefore darker) waters. A subsequent increase of the lens's refractive index probably resulted in an in-focus image being formed. The development of the lens in camera-type eyes probably followed a different trajectory. The transparent cells over a pinhole eye's aperture split into two layers, with liquid in between. The liquid originally served as a circulatory fluid for oxygen, nutrients, wastes,"
"of the size of the pupil, regulation and suppression of the hormone melatonin and entrainment of the body clock. The eye is not shaped like a perfect sphere, rather it is a fused two-piece unit, composed of the anterior segment and the posterior segment. The anterior segment is made up of the cornea, iris and lens. The cornea is transparent and more curved, and is linked to the larger posterior segment, composed of the vitreous, retina, choroid and the outer white shell called the sclera. The cornea is typically about 11.5 mm (0.3 in) in diameter, and 1/2 mm (500"