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66-513: A visor (also spelled vizor ) is a surface that protects the eyes , such as shading them from the sun or other bright light or protecting them from objects. Nowadays many visors are transparent, but before strong transparent substances such as polycarbonate were invented, visors were opaque like a mask . Some modern devices called visors are similar, for example: Types of modern transparent visors include: Eye protection Eye protection are typically separated into categories based on

132-400: A combination of Rayleigh scattering and a moderate amount of melanin in the iris' anterior border layer. Hazel eyes often appear to shift in color from a brown to a green. Although hazel mostly consists of brown and green, the dominant color in the eye can either be brown/gold or green. This is why hazel eyes can be mistaken as amber and vice versa. The combination can sometimes produce

198-402: A first lens (the cornea—the clear part of the eye ) that accounts for most of the optical power of the eye and accomplishes most of the focusing of light from the outside world; then an aperture (the pupil ) in a diaphragm (the iris—the coloured part of the eye ) that controls the amount of light entering the interior of the eye; then another lens (the crystalline lens ) that accomplishes

264-565: A multicolored iris, i.e., an eye that is light brown/amber near the pupil and charcoal or dark green on the outer part of the iris (or vice versa) when observed in sunlight. Definitions of the eye color hazel vary: it is sometimes considered to be synonymous with light brown or gold, as in the color of a hazelnut shell. Around 18% of the US population and 5% of the world population have hazel eyes. Hazel eyes are found in Europe , most commonly in

330-524: A particular (or small range of) wavelength(s), customized to the laser being viewed. Laser protection eye wear is particularly important because of the extremely high intensity of laser light. Welding glass protects against glare and flying sparks. It is a more extreme implementation of the same idea as sunglasses , suited to the more intense light generated during welding . Arc welding goggles must be much darker than blowtorch goggles . Shades 12, 13, and 14 welding glass must be used to stare directly at

396-510: A saccade and larger than a microsaccade, subtend up to one tenth of a degree. Researchers vary in their definition of microsaccades by amplitude. Martin Rolfs states that 'the majority of microsaccades observed in a variety of tasks have amplitudes smaller than 30 min-arc'. However, others state that the "current consensus has largely consolidated around a definition of microsaccades that includes magnitudes up to 1°." The vestibulo-ocular reflex

462-536: A solid gold hue. Even though amber is similar to gold, some people have russet or copper colored amber eyes that are mistaken for hazel, though hazel tends to be duller and contains green with red/gold flecks, as mentioned above. Amber eyes may also contain amounts of very light gold-ish gray. People with that eye color are common in northern Europe , and in fewer numbers in southern Europe, the Middle East , North Africa , and South America . Hazel eyes are due to

528-434: A static contrast ratio of around 100:1 (about 6.5 f-stops ). As soon as the eye moves rapidly to acquire a target ( saccades ), it re-adjusts its exposure by adjusting the iris, which adjusts the size of the pupil. Initial dark adaptation takes place in approximately four seconds of profound, uninterrupted darkness; full adaptation through adjustments in retinal rod photoreceptors is 80% complete in thirty minutes. The process

594-480: A surgical area, such as cornea , cataracts , laser , retina , or oculoplastics . Eye care professionals include: Almost all mammals have brown or darkly-pigmented irises. In humans, brown is by far the most common eye color, with approximately 79% of people in the world having it. Brown eyes result from a relatively high concentration of melanin in the stroma of the iris, which causes light of both shorter and longer wavelengths to be absorbed. In many parts of

660-403: A volume of 6 cubic centimetres (0.37 cu in). The eyeball grows rapidly, increasing from about 16–17 mm (0.63–0.67 in) diameter at birth to 22.5–23 mm (0.89–0.91 in) by three years of age. By age 12, the eye attains its full size. The eye is made up of three coats, or layers, enclosing various anatomical structures. The outermost layer, known as the fibrous tunic ,

726-441: Is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement in response to neural input from the vestibular system of the inner ear, thus maintaining the image in the centre of the visual field. For example, when the head moves to the right, the eyes move to the left. This applies for head movements up and down, left and right, and tilt to

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792-801: Is a device used to protect wearer's entire face (or part of it) from hazards such as impact, splash, heat, or glare. With face shields, as with welding helmets and hand shields, the user is continually lifting and lowering the visor. To protect the eyes when the visor is lifted, spectacles should be worn underneath. A respirator is a device designed to protect the wearer from inhaling particulate matter, including airborne microorganisms, fumes, vapours and gases. Insects like flies, bees, and wasps can fly at high speeds and come into contact with your eyes. Their wings or stingers can cause irritation or even scratch your cornea, which can be painful and potentially cause long-term damage. Small projectiles and fragments generated from processes like grinding or machining can have

858-417: Is an area of 4.17 steradians or 13700 square degrees for binocular vision. When viewed at large angles from the side, the iris and pupil may still be visible by the viewer, indicating the person has peripheral vision possible at that angle. About 15° temporal and 1.5° below the horizontal is the blind spot created by the optic nerve nasally, which is roughly 7.5° high and 5.5° wide. The retina has

924-482: Is caused by the combination of: 1) an amber or light brown pigmentation in the stroma of the iris (which has a low or moderate concentration of melanin) with: 2) a blue shade created by the Rayleigh scattering of reflected light. Green eyes contain the yellowish pigment lipochrome . The inheritance pattern followed by blue eyes was previously assumed to be a mendelian recessive trait, however, eye color inheritance

990-493: 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

1056-411: Is composed of the cornea and sclera , which provide shape to the eye and support the deeper structures. The middle layer, known as the vascular tunic or uvea , consists of the choroid , ciliary body , pigmented epithelium and iris . The innermost is the retina , which gets its oxygenation from the blood vessels of the choroid (posteriorly) as well as the retinal vessels (anteriorly). The spaces of

1122-440: 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. The approximate field of view 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

1188-415: 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 (0.45 in) in diameter, and 0.5 mm (500 μm) in thickness near its centre. The posterior chamber constitutes the remaining five-sixths; its diameter is typically about 24 mm (0.94 in). An area termed the limbus connects

1254-459: Is nonlinear and multifaceted, so an interruption by light exposure requires restarting the dark adaptation process over again. The human eye can detect a luminance from 10 cd/m , or one millionth (0.000001) of a candela per square meter to 10 cd/m or one hundred million (100,000,000) candelas per square meter. (that is it has a range of 10 , or one hundred trillion 100,000,000,000,000, about 46.5 f-stops). This range does not include looking at

1320-467: Is now recognized as a polygenic trait , meaning that it is controlled by the interactions of several genes. Blue eyes are predominant in northern and eastern Europe, particularly around the Baltic Sea . Blue eyes are also found in southern Europe, Central Asia , South Asia , North Africa and West Asia . Approximately 8% to 10% of the global population have blue eyes. A 2002 study found that

1386-476: Is sensitive to intense light because it damages the retina and can even blind the individual. There are many different types of eye protection against light suited for different applications. The most common forms of eye protection against light are sunglasses . These primarily protect against UV light from the sun and help increase visibility in bright conditions. They often tend to be fashionable as well as practical. Laser protection eyewear will filter out

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1452-789: The Netherlands and the United Kingdom , and have also been observed to be very common among the Low Saxon speaking populations of northern Germany. Green eyes are most common in Northern , Western and Central Europe . Around 8–10% of men and 18–21% of women in Iceland and 6% of men and 17% of women in the Netherlands have green eyes. Among European Americans , green eyes are most common among those of recent Celtic and Germanic ancestry, with about 16%. The green color

1518-425: The ciliary muscles surrounding the lens; this process is known as "accommodation". Accommodation narrows the inner diameter of the ciliary body, which actually relaxes the fibers of the suspensory ligament attached to the periphery of the lens, and also allows the lens to relax into a more convex, or globular, shape. A more convex lens refracts light more strongly and focuses divergent light rays from near objects onto

1584-423: 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 . In order, along the optic axis, the optical components consist of

1650-404: The eye movements , the seventh controls the movement of the upper eyelid . The six muscles are four recti muscles – the lateral rectus , the medial rectus , the inferior rectus , and the superior rectus , and two oblique muscles the inferior oblique , and the superior oblique . The seventh muscle is the levator palpebrae superioris muscle . When the muscles exert different tensions, a torque

1716-399: The nervous system : rods respond to low intensity light and contribute to perception of low-resolution, black-and-white images; cones respond to high intensity light and contribute to perception of high-resolution, coloured images; and the recently discovered photosensitive ganglion cells respond to a full range of light intensities and contribute to adjusting the amount of light reaching

1782-404: The pupil . A thin layer called the conjunctiva sits on top of this. The front part is also called the anterior segment of the eye. The eye is not shaped like a perfect sphere; rather it is a fused two-piece unit, composed of an anterior (front) segment and the posterior (back) segment. The anterior segment is made up of the cornea, iris and lens. The cornea is transparent and more curved and

1848-429: The ability of debris to get behind the lenses from the side. Safety glasses can often mount insert frames to mount prescription corrective lenses for users with suboptimal vision. Such insert frames are mounted behind the protective lens. In some applications, regular eye wear, if manufactured from high-impact materials, can be worn with removable side shields. Oversized spectacles are also manufactured, designed to sit over

1914-408: The better-focused centre. In the eye, the pupil serves this purpose by constricting while the eye is focused on nearby objects. Small apertures also give an increase in depth of field , allowing a broader range of "in focus" vision. In this way the pupil has a dual purpose for near vision: to reduce spherical aberration and increase depth of field. Changing the curvature of the lens is carried out by

1980-476: The brain to determine the depth and distance of an object, called stereovision, and gives the sense of three-dimensionality to the vision. Both eyes must point accurately enough that the object of regard falls on corresponding points of the two retinas to stimulate stereovision; otherwise, double vision might occur. Some persons with congenitally crossed eyes tend to ignore one eye's vision, thus do not suffer double vision, and do not have stereovision. The movements of

2046-401: The brow), 45° nasal (limited by the nose), 70° inferior (down), and 100° temporal (towards the temple). For both eyes, combined ( binocular vision ) visual field is approximately 100° vertical and a maximum 190° horizontal, approximately 120° of which makes up the binocular field of view (seen by both eyes) flanked by two uniocular fields (seen by only one eye) of approximately 40 degrees. It

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2112-423: 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. Each eye has seven extraocular muscles located in its orbit . Six of these muscles control

2178-401: The cornea and sclera. The iris is the pigmented circular structure concentrically surrounding the centre 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

2244-406: 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 visual system in the human brain is too slow to process information if images are slipping across the retina at more than a few degrees per second. Thus, to be able to see while moving, the brain must compensate for the motion of

2310-462: The eye are controlled by six muscles attached to each eye, and allow the eye to elevate, depress, converge, diverge and roll. These muscles are both controlled voluntarily and involuntarily to track objects and correct for simultaneous head movements. Rapid eye movement, REM, typically refers to the sleep stage during which the most vivid dreams occur. During this stage, the eyes move rapidly. Saccades are quick, simultaneous movements of both eyes in

2376-404: The eye are filled with the aqueous humour anteriorly, between the cornea and lens, and the vitreous body , a jelly-like substance, behind the lens, filling the entire posterior cavity. The aqueous humour is a clear watery fluid that is contained 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

2442-404: The eye at up to 100°/s in adult humans. It is more difficult to visually estimate speed in low light conditions or while moving, unless there is another point of reference for determining speed. The optokinetic reflex (or optokinetic nystagmus) stabilizes the image on the retina through visual feedback. It is induced when the entire visual scene drifts across the retina, eliciting eye rotation in

2508-463: The eyes from salt or chlorine . Cover goggles are designed to be worn over eye wear. Like eyecup goggles, they have adjustable or elasticized headbands and are equipped with direct or indirect ventilation ports to allow air in and prevent fogging. While both models keep out large particles, indirect-vented goggles are better at keeping out liquids and dusts. A welding helmet is a type of headgear used when performing certain types of welding to protect

2574-470: The eyes in the form of splash, mists, vapors, or fumes. When working with or around chemicals, it is important to know the location of emergency eyewash stations and how to access them with restricted vision. When fitted and worn correctly, goggles protect your eyes from hazardous substances. A face shield may be required in areas where workers are exposed to severe chemical hazards. Personal protective equipment devices for chemical hazards: The human eye

2640-587: The eyes, face and neck from flash burn, ultraviolet light, sparks, infrared light, and heat. A welding hand shield is a metal plate containing the same protective lens as a welding helmet with a handle on the bottom, intended to be held up in front of the face while working. Hoods (or non-rigid helmets) come with impact-resistant windows usually made of plastic or similar material. An air-supply system may also be incorporated. Hoods are made of non-rigid material for use in confined spaces and of collapsible construction for convenience in carrying and storing. A face shield

2706-422: The head by turning the eyes. Frontal-eyed animals have a small area of the retina with very high visual acuity, the fovea centralis . It covers about 2 degrees of visual angle in people. To get a clear view of the world, the brain must turn the eyes so that the image of the object of regard falls on the fovea. Any failure to make eye movements correctly can lead to serious visual degradation. Having two eyes allows

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2772-599: The iris. Eye irritation has been defined as "the magnitude of any stinging, scratching, burning, or other irritating sensation from the eye". It is a common problem experienced by people of all ages. Related eye symptoms and signs of irritation are discomfort, dryness, excess tearing, itchiness, grating, foreign body sensation, ocular fatigue, pain, soreness, redness, swollen eyelids, and tiredness, etc. These eye symptoms are reported with intensities from mild to severe. It has been suggested that these eye symptoms are related to different causal mechanisms, and symptoms are related to

2838-444: The light that is reflected from the epithelium undergoes Mie scattering (which is not strongly frequency-dependent) rather than Rayleigh scattering (in which shorter wavelengths of light are scattered more). This would be analogous to the change in the color of the sky, from the blue given by the Rayleigh scattering of sunlight by small gas molecules when the sky is clear, to the gray caused by Mie scattering of large water droplets when

2904-423: 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. The size of the eye differs among adults by only one or 2 millimetres. The eyeball is generally less tall than it is wide. The sagittal vertical (height) of a human adult eye is approximately 23.7 mm (0.93 in),

2970-471: The midday sun (10 cd/m ) or lightning discharge. At the low end of the range is the absolute threshold of vision for a steady light across a wide field of view, about 10 cd/m (0.000001 candela per square meter). The upper end of the range is given in terms of normal visual performance as 10 cd/m (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

3036-417: The particular ocular anatomy involved. Several suspected causal factors in our environment have been studied so far. One hypothesis is that indoor air pollution may cause eye and airway irritation. Eye irritation depends somewhat on destabilization of the outer-eye tear film, i.e. the formation of dry spots on the cornea, resulting in ocular discomfort. Occupational factors are also likely to influence

3102-957: The perception of eye irritation. Some of these are lighting (glare and poor contrast), gaze position, reduced blink rate, limited number of breaks from visual tasking, and a constant combination of accommodation, musculoskeletal burden, and impairment of the visual nervous system. Another factor that may be related is work stress. In addition, psychological factors have been found in multivariate analyses to be associated with an increase in eye irritation among VDU users. Other risk factors, such as chemical toxins/irritants (e.g. amines , formaldehyde , acetaldehyde , acrolein , N-Decane , VOCs , ozone , pesticides and preservatives , allergens , etc.) might cause eye irritation as well. Certain volatile organic compounds that are both chemically reactive and airway irritants may cause eye irritation. Personal factors (e.g. use of contact lenses, eye make-up, and certain medications) may also affect destabilization of

3168-547: The potential to penetrate some types of protective eye-wear. In the United States the ANSI/ISEA Z87.1-2020 standard is used to certify protective eye-wear which is capable of protecting from these hazards. Debris such as dust, dirt, and small rocks can be picked up by the wind and fly into your eyes. This can cause discomfort and potentially lead to a corneal abrasion or infection. Ultraviolet (UV) radiation from

3234-412: The prevalence of blue eye color among the white population in the United States to be 33.8% for those born from 1936 through 1951. Like blue eyes, gray eyes have a dark epithelium at the back of the iris and a relatively clear stroma at the front. One possible explanation for the difference in the appearance of gray and blue eyes is that gray eyes have larger deposits of collagen in the stroma, so that

3300-481: The region. Amber eyes are a solid color with a strong yellowish/golden and russet/coppery tint, which may be due to the yellow pigment called lipochrome (also found in green eyes). Amber eyes should not be confused with hazel eyes. Although hazel eyes may contain specks of amber or gold, they usually tend to have many other colors, including green, brown and orange. Also, hazel eyes may appear to shift in color and consist of flecks and ripples, while amber eyes are of

3366-414: The remaining focusing of light into images ; and finally a light-sensitive part of the eye (the retina ), where the images fall and are processed. The retina makes a connection to the brain via the optic nerve . The remaining components of the eye keep it in its required shape, nourish and maintain it, and protect it. Three types of cells in the retina convert light energy into electrical energy used by

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3432-455: The retina in both eyes. To look at a nearby object, the eyes rotate 'towards each other' ( convergence ), while for an object farther away they rotate 'away from each other' ( divergence ). Lenses cannot refract light rays at their edges as well as closer to the centre. The image produced by any lens is therefore somewhat blurry around the edges ( spherical aberration ). It can be minimized by screening out peripheral light rays and looking only at

3498-655: The retina, allowing closer objects to be brought into better focus. The human eye contains enough complexity to warrant specialized attention and care beyond the duties of a general practitioner . These specialists, or eye care professionals , serve different functions in different countries. Eye care professionals can have overlap in their patient care privileges. For example, both an ophthalmologist (M.D.) and optometrist (O.D.) are professionals who diagnose eye disease and can prescribe lenses to correct vision. Typically, only ophthalmologists are licensed to perform surgical procedures. Ophthalmologists may also specialize within

3564-405: The retina, to regulating and suppressing the hormone melatonin , and to entraining circadian rhythm . Humans have two eyes, situated on the left and the right of the face . The eyes sit in bony cavities called the orbits , in the skull . There are six extraocular muscles that control eye movements. The front visible part of the eye is made up of the whitish sclera , a coloured iris , and

3630-449: The right and left, all of which give input to the ocular muscles to maintain visual stability. 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

3696-407: The same direction and at a velocity that minimizes the motion of the image on the retina. When the gaze direction deviates too far from the forward heading, a compensatory saccade is induced to reset the gaze to the centre of the visual field. For example, when looking out of the window at a moving train, the eyes can focus on a moving train for a short moment (by stabilizing it on the retina), until

3762-421: The same direction controlled by the frontal lobe of the brain. Even when looking intently at a single spot, the eyes drift around. This ensures that individual photosensitive cells are continually stimulated in different degrees. Without changing input, these cells would otherwise stop generating output. Eye movements include drift, ocular tremor , and microsaccades. Some irregular drifts, movements smaller than

3828-447: 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

3894-614: The sky is cloudy. Alternatively, it has been suggested that gray and blue eyes might differ in the concentration of melanin at the front of the stroma. Gray eyes can also be found among the Algerian Shawia people of the Aurès Mountains in Northwest Africa, in the Middle East / West Asia , Central Asia , and South Asia . Under magnification, gray eyes exhibit small amounts of yellow and brown color in

3960-518: The style of eye wear and the hazard they are designed to reduce. There categories include: Spectacles with side protection; Goggles ; Welding helmet ; Welding Hand Shields; Non-Rigid Helmets (hoods); Face shield ; and Respirator Face pieces. Safety glasses or spectacles, although often used as a catch-all term for all types of eye protection, specifically revers to protective equipment that closely resembles common eye wear. To meet most national standards, spectacles must include side shields to reduce

4026-496: The sun can also harm your eyes. Prolonged exposure to UV rays can cause cataracts, macular degeneration, and other eye conditions that can lead to vision loss. A large percentage of eye injuries are caused by direct contact with chemicals. These injuries often result from an inappropriate choice of personal protective equipment that allows a chemical substance to enter from around or under protective eye equipment. Serious and irreversible damage can occur when chemical substances contact

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4092-406: The sun or a solar eclipse. These higher index shades are suitable for arc welding and therefore are suitable for solar viewing. Sunglasses will not provide sufficient protection. Some helmets and visors also protect the eyes: Human eye The human eye is a sensory organ in the visual system that reacts to visible light allowing eyesight . Other functions include maintaining

4158-400: The train moves out of the field of vision. At this point, the eye is moved back to the point where it first saw the train (through a saccade). The adjustment to close-range vision involves three processes to focus an image on the retina. When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the projection of the image is in the centre of

4224-425: The transverse horizontal diameter (width) is 24.2 mm (0.95 in) and the axial anteroposterior size (depth) averages 22.0–24.8 mm (0.87–0.98 in) with no significant difference between sexes and age groups. Strong correlation has been found between the transverse diameter and the width of the orbit (r = 0.88). The typical adult eye has an anterior to posterior diameter of 24 mm (0.94 in), and

4290-500: The users normal eye wear. Goggles are forms of protective eyewear that enclose the eye area in order to prevent particulates, infectious fluids, or chemicals from striking the eyes. Goggles come in two styles, eyecup goggles, and cover goggles. Eyecup goggles completely cover the eye socket to give all-round protection. They have adjustable or elasticized headbands and often are equipped with ventilation ports to allow air in and prevent fogging. For example, swimming goggles to protect

4356-683: The world, it is nearly the only iris color present. Brown eyes are common in Europe , East Asia , Southeast Asia , Central Asia , South Asia , West Asia , Oceania , Africa and the Americas . Light or medium-pigmented brown eyes can also be commonly found in Europe , among the Americas , and parts of Central Asia , West Asia and South Asia . Light brown eyes bordering amber and hazel coloration are common in Europe, but can also be observed in East Asia and Southeast Asia, though are uncommon in

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