The human eye is the best possible optical camera
Reference sources note that the human eye shares optical principles and functional resemblances with cameras, but whether it is the best possible optical camera is not established by the evidence.
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Human eye. https://en.wikipedia.org/wiki/Human_eye
keeping balance. The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer layers, such as the outermost, The human eye is a sensory organ in the visual system that reacts to visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and keeping balance. The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer layers, such as the outermost, white part of the eye (the sclera) and one of its inner layers (the pigmented The eye includes a lens similar to lenses found in optical instruments such as cameras and the same physics principles can be applied. The pupil of the human eye is its aperture; the iris is the diaphragm that serves as the aperture stop. Refraction in the cornea causes the effective aperture (the entrance pupil) to differ slightly from the physical pupil diameter. The entrance pupil is typically about 4 mm in diameter, although it can range from 2 mm (f/8.3) in a brightly lit place to 8 mm (f/2.1) in the dark. The latter value decreases slowly with age; older people's eyes sometimes dilate to not more than 5–6mm in the dark, and may be as small as 1mm in the light. The human eye is a sensory organ in the visual system that reacts to visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and keeping balance. The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer layers, such as the outermost, white part of the eye (the sclera) and one of its inner layers (the pigmented choroid) keeping the eye essentially light tight except on the eye's optic axis. 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 (accommodation) and is controlled by the ciliary muscle. Between the two lenses (the cornea and the crystalline lens), there are four optical surfaces which each refract light as it travels along the optical path. One basic model describing the geometry of the optical system is the Arizona Eye Model. This model describes the accommodation of the eye geometrically. Photons of light falling on the light-sensitive cells of the retina (photoreceptor cones and rods) are converted into electrical signals that are transmitted to the brain by the optic nerve and interpreted as sight and vision. === Development === The human eye primarily develops from the ectoderm. The lens and the epithelium of the cornea arise from the surface ectoderm directly; other structures come from either the neural ectoderm or the neural crest, which itself arises from the ectoderm. The mesoderm has limited contributions: it is the origin of the vitreous body, the blood vessels of the eye, and the When the muscles exert different tensions, a torque is exerted on the globe that causes it to turn, in almost pure rotation, with only about one millimeter of translation. Thus, the eye can be considered as undergoing rotations about a single point in the centre of the eye. == Vision == === Visual field === The approximate visual field of an individual human eye (measured from the fixation point, i.e., the point at which one's gaze is directed) varies by facial anatomy, but is typically 30° superior (up, limited by the brow), 45° nasal (limited by the nose), 70° inferior (down), and 107° temporal (towards the temple).. The upper end of the range is given in terms of normal visual performance as 108 cd/m2 (100,000,000 or one hundred million candelas per square meter). The eye includes a lens similar to lenses found in optical instruments such as cameras and the same physics principles can be applied. The pupil of the human eye is its aperture; the iris is the diaphragm that serves as the aperture stop. Refraction in the cornea causes the effective aperture (the entrance pupil) to differ slightly from the physical pupil diameter. The entrance pupil is typically about 4 mm in diameter, although it can range from 2 mm (f/8.3) in a brightly lit place to 8 mm (f/2.1) in the dark. This applies for head movements up and down, left and right, and tilt to the right and left, all of which give input to the ocular muscles to maintain visual stability. === Smooth pursuit === Eyes can also follow a moving object around. This tracking is less accurate than the vestibulo-ocular reflex, as it requires the brain to process incoming visual information and supply feedback. Following an object moving at constant speed is relatively easy, though the eyes will often make saccades to keep up. The smooth pursuit movement can move the eye at up to 100°/s in adult humans. As the light waves enter the eye, they excite electrons that can cause harm to the cells in the eye, but they can cause oxidative damage that may lead to macular degeneration or cataracts. Lutein and zeaxanthin bind to the electron free radical and are reduced rendering the electron safe. There are many ways to ensure a diet rich in lutein and zeaxanthin, the best of which is to eat dark green vegetables including kale, spinach, broccoli and turnip greens. Nutrition is an important aspect of the ability to achieve and maintain proper eye health. Pupil size has also been shown to play an influential role in attraction and nonverbal communication, with dilated (larger) pupils perceived to be more attractive. It should also be noted that dilated pupils are a response to sexual arousal and stimuli. In the Renaissance, women used the juice of the berries of the belladonna plant in eyedrops to dilate the pupils and make the eyes appear more seductive. == Images == == See also == == References == == External links == Eye – Hilzbook Retina – Hilzbook Media related to Human eyes at Wikimedia Commons Quotations related to eyes at Wikiquote
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Popular Science Monthly/Volume 1/August 1872/Sight and the Visual Organ. https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_1/August_1872/Sight_and_the_Visual_Organ
plate in a camera -obscura, we shall perceive that the eye has indeed an undeniable resemblance with this well-known optical instrument, the camera -obscura First, then, the umbellar expansion of the optic nerve, the retina, enables us to make experiments; this retina being in such close contact with the eye, the optical part of the visual organ, that it is accessible to every sort of mechanical irritation. You have yourselves, consciously or unconsciously, often made such experiments, when you watched the circles and sparks of fire and light, which become visible on rubbing or pressing your eyes through their lids, or striking them with a hard substance. Here the eye, as an optical apparatus, remains passive. As, on the one hand, the retina stands as the terminal apparatus of the optic nerve; on the other hand, it acts as a shade subservient to optical purposes; a screen, on which a perspective picture of the outside world is projected. If you compare it with the dull glass on which the picture in the camera-obscura falls, or the prepared plate in the photographer's camera, you have a correct notion of what I mean. As, in the photographer's camera, the picture falls on the sensitive plate, and is impressed on it by means of chemical changes produced by light, so in the eye it falls on the sensitive plate of the retina, whose irritations are telegraphed to the brain in due form. We henceforth have to consider this image painted on the retina as the real object of the operations of the senses. But how does the picture imprint itself on the retina? This is done by an optical apparatus close behind the retina and in connection with it; and, in short, by means of that mechanism known to us as the eye . If we compare the retina with the sensitive plate in a camera-obscura, we shall perceive that the eye has indeed an undeniable resemblance with this well-known optical instrument, the camera-obscura. Fig. 2. S, Sclerotic; C, Cornea; L, Crystalline Lens; K, Aqueous Humor; K', Vitreous Humor; A, Choroid; N, Optic Nerve and Retina. And, lastly, overlying the interior surface of the sclerotic, is the choroid with its pigment, being the substitute for the black paint in the camera. You find it marked with an A. Now, if this eye with its cornea, like a camera-obscura with its window, is turned on the objects of the outer world, we shall behold what Fig. 3 shows us: The light proceeding from a point A, beyond the eye, throws a pencil of rays on the cornea; this is already refracted here and there on the surface of the lens, but in a manner so as to collect all its rays again in the one point a of the retina. This a , then, is the image-point of the object-point A. Thinking of the dazzling and delusive visions which are a consequence of the gradual consuming away of the pigment in the choroid, or which accompany the entire want of it, as with the albinos, we cannot doubt that one  ​ essential design of this tissue is to intercept the scattered rays. But, apart from its office of conducting nourishment to the eye, and secreting the humors by means of its numerous blood-vessels, the choroid has a second optical design to fulfil, which now brings us to the characteristic signs of the eye. As you will perceive from Fig. It regulates the entrance of the light , being furnished with a muscular apparatus (ciliary muscle), which provides that in strong light the pupil contracts, and in duller light expands. Thus the iris plays the part of a so-called movable diaphragm, a common appliance in optical instruments, used to dull the light for the purpose of seeing better. You cannot but have observed this play of the pupil, and how it accommodates itself to the volume of light; nor can you be ignorant that the iris with its varied coloring from light blue to deepest brown is what we know as the color of the eye. The requirements made on an optical instrument depending on lenticular effect, are different according as it is expected to project images of nearer or more distant objects. The light with very divergent rays, and proceeding from near objects, is collected to a picture  ​ behind the lens, while that of the distant objects falls with almost parallel lines. To return to the camera-obscura, you must draw out the tube with the lens, in other words, remove the latter farther from the intercepting plate if nearer objects are to be impressed, and on the other, push it in, if more distant ones are wanted. The same effects might be produced at equally the same distance by simply substituting lenses of different power. Now, the human eye has to fulfil the requirement of projecting clearly-defined images on the retina, whether they are but a few inches off, or at an immeasurable distance. The eye being strictly subject to lenticular laws, either the space between the lens and the retina must have More patient and minute investigations have, however, proved that the pupil derives its blackness only partially from the above circumstance, and mostly from the refraction of the light. Helmholtz has succeeded in banishing that darkness from the pupil of the human eye. By a simple arrangement, called the speculum oculi , he uses the light which is reflected from the deeper parts of the eye to illuminate the whole of the interior, as also the image itself projected on the retina. For the rest, it is filled up with a structure of its own; and we have reason for assuming that it furnishes the most exact perceptions, not only on account of the greater optical sharpness of the image, but also on account of the higher energy or activity with which it is endowed. It is this spot we make use of when we desire to go into details; for, if we wish to examine closely into the nature of an object, either we approach it to the eye, or bring the eye to bear on the object; but, in both cases, in such a manner as to cause the image to fall exactly on the hollow of the retina, or on the spot of direct vision .
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