So we have two eyes side by side, giving us binocular stereoscopic vision.\nEach eye has a wide angle of view, and having them side by side gives us a wide angle of view.\nEach eye has a 150\u00b0 field of view, and the two combined have a 180\u00b0 field of view.\nThe side-by-side arrangement of the eyes comes to us from evolution, as most predators have their eyes side-by-side, enabling us to appreciate distances.\nTo appreciate the distance of an object, we need two distinct angles of view.\nPrey, on the other hand, will prefer the widest possible field of vision, even if this means limiting the binocular field of vision, i.e. in 3D, as some birds see 360\u00b0. It should also be noted that the two eyes operate independently. <\/p>
In humans, each eye sees 90\u00b0 outwards and 60\u00b0 inwards.\nThis gives a field of vision of 100\u00b0 in 3D and 40\u00b0 in 2D.\nThe benefits of binocular vision are not limited to 3D vision, but that’s not all!\nBinocular vision also provides double information on the light emanating from a given point, and if this information is doubled, it enables us to perceive dimly-lit objects. <\/p>
How does an eye work?<\/strong><\/p> Well, like a camera’s darkroom.\nWhen light enters the eye, it passes through a first lens, the cornea, then a second lens, the crystalline lens.\nBetween the two, light passes through the pupil, which lets in more or less light, like the diaphragm on a camera. <\/p> How does our pupil work?<\/strong><\/p> In the dark, the pupil dilates to let in more light, a phenomenon we call mydriasis, and conversely the pupil contracts in the presence of light, a phenomenon we call miosis.\nNormally, this is a reflex, but sometimes it doesn’t go as planned.\nA case in point is David Johns, who was punched in the eye during a fight.\nThis had the effect of keeping his pupil permanently open.\nThe effect is called permanent mydriasis, and David Johns is better known as David Bowie. <\/p> Light rays that have passed through the cornea, the center of the pupil and the crystalline lens end up passing through the vitreous body – which makes up most of our transparent eye – and end up on the retina. <\/p> What is the retina and how does it work?<\/strong><\/p> On the surface of the retina we find a host of sensors, cones and rods.\nRods are specialized in acquiring information about light intensity, while cones are specialized in acquiring information about light frequency – cones are specialized in acquiring information about color.\nThey are very bad at low light intensity, which is why we always see in black and white at night.\nRods, on the other hand, are good at light intensity, even at low light levels, and bad at color perception, which is not their role. <\/p> The science of optics<\/strong><\/p> In optics, we call night vision scotopic<\/strong> vision, from the ancient Greek “scotos” meaning darkness and “opsis” meaning sight.\nIn fact, fear of the dark is called scotophobia. <\/p> Daytime or diurnal vision, photopic<\/strong> vision, from “photos”, light, and “opsis”, sight.\nAt dusk or dawn we call the mesopic<\/strong> domain, from “meso” meaning the middle and “opsis”, sight. <\/p> Ocular performance?<\/strong><\/p> Ocular performance<\/strong> is the performance of sight, but only at the level of the eye, without regard to the processing that the brain can make of it: the performance of the eye, considered as an instrument that captures light or images.\nThere are 4 levels of information.\nThere’s sharpness, resolution, contrast and movement. <\/p> The cornea<\/strong><\/p> For sharpness, what counts is the eye’s ability to focus light rays.\nIn the human eye, the cornea is the first lens through which light rays pass.\nIt’s a converging lens, so it’s thicker at the periphery and thinner at the center.\nIt is only 1mm at the periphery and 0.5mm at the center.\nThe cornea is responsible for 70% of the focusing of light rays.\nThe cornea is normally transparent, but it can lose its transparency.\nTo remain transparent, the cornea needs to bathe, remaining in a hydrated environment with 80% water per milligram of tissue.\nThis is a vestige of our aquatic life, when we lived underwater. <\/p> The cornea is made up of 6 layers (the sixth layer was discovered in 2013).\nFrom the outer to the inner layer: <\/p> Where do the light rays that have passed through the cornea go?<\/strong><\/p> Light rays pass through the anterior chamber of <\/strong>the eye, the area between the cornea and the iris.\nThe iris is the colored part surrounding the pupil.\nThis anterior chamber is made up of aqueous humor<\/strong>, which is 90% water and other components such as chlorine and sodium, i.e. salt.\nThe role of this liquid is to maintain a constant pressure in the eye in general, but also to nourish and repair the cornea.\nThe pressure at this level of the eye increases over the years, and when this pressure becomes too great, glaucoma<\/strong> develops, progressively damaging the visual cells and causing progressive blindness. <\/p> On the other hand, light rays pass through the posterior chamber of<\/strong>the eye, the area between the iris and the lens.\nThis, too, is made up of the aqueous humor secreted by the ciliary muscle, which enables the lens to move. <\/p> Le vitr\u00e9<\/strong><\/p> After the lens, we find the vitreous.\nA sort of gel, identical in composition to the cornea, it is composed of 90% water, collagen fibers and protein.\nVitreous humor is the component of the vitreous and makes up 90% of the entire eye.\nIts role is to maintain the shape of the eye and press the retina against the back of the eye.\nRetinal detachment occurs when the aqueous humor slips between the retina and the pigmented epithelium, detaching the retina.\nIf this membrane detaches, vision loss is immediate and may be irreversible.\nSurgical intervention within hours of the detachment’s appearance can save part of the visual field. <\/p> The lens<\/strong><\/p> It is important for sharpness.\nThis lens is capable of accommodation.\nAccommodation is the eye’s ability to see objects both near and far.\nWith a diameter of 1 centimeter and half its thickness, the lens is held in place by the ciliary muscle, which, by contracting and dilating, modifies its shape to make it more or less curved.\nAs a result, light rays passing through it focus on a more or less distant point. <\/p> What happens when light rays reach the eye<\/strong>?<\/p> Light generally travels in a straight line as long as it remains in the same medium.\nSo light in air travels in a straight line, but as soon as it passes through another medium, a refraction process takes place: the ray is deflected.\nAs it passes through the eye, light rays pass through several media and are refracted several times, ending up on the retina, projecting an image of what we’re observing outside.\nThis is the principle of the darkroom. <\/p> When these rays converge on the retina, they activate the cone and rod photoreceptors, which send information about light intensity and frequency to the brain.\nColor and light intensity.\nTo understand the notion of contrast and resolution, to have an image that is well defined and correctly marks light variations.\nWe need to look at how the cones and rods are distributed on the surface of the retina. <\/p> Directly in front of the pupil, at the back of the eye, lies a cone-dense zone called the macula, 5mm in diameter.\nThis is precisely the most cone-dense area of our eye, and within it lies the even more cone-rich fovea.\nBecause this zone is so cone-rich, it is able to transmit a great deal of color information.\nThis zone has a high resolution, but beware, as this zone has a high concentration of cones and not rods, we have a high resolution in the photopic period, during the day.\nIn the dark, this zone doesn’t work very well… In the fovea, there are no rods and its structure is quite astonishing, a honeycomb pattern of cones.\nIt has been mathematically proven that honeycomb paving is the optimum paving for covering the largest surface area with the smallest joint perimeter. <\/p> As we move away from the macula, we find more and more rods and less and less cones.\nThis means that, in terms of ocular performance, right at the center of the pupil, at the center of our vision, we have an area that is really high-resolution and high-contrast.\nAs we move away from the center of our vision, we lose resolution and contrast.\nNote that we won’t lose sharpness.\nOn the contrary, we’ll have better information on light intensity.\nThat’s why we can easily make out the flashing lights of police cars in our field of vision. <\/p> How do we detect movement with our eyes?<\/strong><\/p> When the resolution is fine enough to detect reasonable movement (under the right conditions), the question of movement is purely a question of image refreshment.\nHow fast is the eye able to refresh the image and send it to the brain?\nFor a camera, this is called FPS, but for the eye it’s a little more different: it’s how often the cone or rod is able to acquire new information and transmit it to the brain.\nWe’re capable of watching films of 25 to 30 frames per second on TV or YouTube.\nWhat we observe is that a subject confronted with a stroboscopic light of 50 to 60 flashes per second sees a persistent light. <\/p> What is the blind spot or papilla of our eye?<\/strong><\/p> In the retina, there is an area of the eye where the optic nerve is inserted and where blood vessels arrive and leave.\nMechanically, there can be no photoreceptors in this area. <\/p> Eyes and ultraviolet rays<\/strong><\/p> On the retina we have cone and rod photoreceptors.\nThe rods contain a protein pigment, Rhodopsin <\/strong>, which is sensitive to ultraviolet light.\nIf our crystalline lens combined with the vitreous did not absorb ultraviolet light, we would be fully able to see it.\nThis is a frequency that rods shouldn’t normally see, as they don’t perceive colors… <\/p>","protected":false},"excerpt":{"rendered":" So we have two eyes side by side, giving us binocular stereoscopic vision. Each eye has a wide angle of view, and having them side by side gives us a wide angle of view. Each eye has a 150\u00b0 field of view, and the two combined have a 180\u00b0 field of view. The side-by-side arrangement […]<\/p>\n","protected":false},"author":990105,"featured_media":12821,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-16374","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-masonry-2-columns"],"yoast_head":"\n