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83-414: The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina . It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil. The size of the pupil is controlled by the iris, and varies depending on many factors ,

166-608: A laxative or enemas . Treatment of OIC is successional and dependent on severity. The first mode of treatment is non-pharmacological, and includes lifestyle modifications like increasing dietary fiber , fluid intake (around 1.5 L (51 US fl oz) per day), and physical activity . If non-pharmacological measures are ineffective, laxatives , including stool softeners ( e.g. , polyethylene glycol ), bulk-forming laxatives ( e.g. , fiber supplements ), stimulant laxatives ( e.g. , bisacodyl , senna ), and/or enemas , may be used. A common laxative regimen for OIC

249-408: A contractile structure, consisting mainly of smooth muscle , surrounding the pupil. Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. This is known as the pupillary light reflex . The iris contains two groups of smooth muscles; a circular group called the sphincter pupillae , and a radial group called the dilator pupillae . When

332-446: A dark ring encircling the iris on some individuals, but is a result of the optical properties of the region between the cornea and sclera , not of pigments in the iris. Iris color is a highly complex phenomenon consisting of the combined effects of texture, pigmentation, fibrous tissue, and blood vessels within the iris stroma , which together make up an individual's epigenetic constitution in this context. An organism's "eye color"

415-791: A non-oral route ( e.g. subcutaneous for metoclopramide, rectally for domperidone). Evidence suggests that opioid-inclusive anaesthesia is associated with postoperative nausea and vomiting. Patients with chronic pain using opioids had small improvements in pain and physically functioning and increased risk of vomiting. Tolerance to drowsiness usually develops over 5–7 days, but if troublesome, switching to an alternative opioid often helps. Certain opioids such as fentanyl , morphine and diamorphine (heroin) tend to be particularly sedating, while others such as oxycodone , tilidine and meperidine (pethidine) tend to produce comparatively less sedation, but individual patients responses can vary markedly and some degree of trial and error may be needed to find

498-448: A patient's systemic health. Practitioners match their observations to "iris charts", which divide the iris into zones corresponding to specific parts of the human body. Iridologists see the eyes as "windows" into the body's state of health. Iridology is not supported by quality research studies, and is considered pseudoscience. Opioids Opioids are a class of drugs that derive from, or mimic, natural substances found in

581-451: A result, their irises are unable to dilate and contract, so that the pupil always remains of a fixed size. From anterior (front) to posterior (back), the layers of the iris are: The stroma and the anterior border layer of the iris are derived from the neural crest , and behind the stroma of the iris, the sphincter pupillae and dilator pupillae muscles, as well as the iris epithelium, develop from optic cup neuroectoderm. The iris controls

664-464: A similar link between foraging behaviour and pupil shape amongst the felidae and canidae discussed above. A 2015 study confirmed the hypothesis that elongated pupils have increased dynamic range, and furthered the correlations with diel activity. However it noted that other hypotheses could not explain the orientation of the pupils. They showed that vertical pupils enable ambush predators to optimise their depth perception, and horizontal pupils to optimise

747-520: A successful long-term care strategy for those with chronic cancer pain . Just over half of all states in the US have enacted laws that restrict the prescribing or dispensing of opioids for acute pain. Guidelines have suggested that the risk of opioids is likely greater than their benefits when used for most non-cancer chronic conditions including headaches , back pain , and fibromyalgia . Thus they should be used cautiously in chronic non-cancer pain. If used

830-508: A synergistic pain relieving effect permitting smaller doses of opioids be used. Consequently, several opioid/antihistamine combination products have been marketed, such as Meprozine ( meperidine / promethazine ) and Diconal ( dipipanone / cyclizine ), and these may also reduce opioid induced nausea. Opioid-induced constipation (OIC) develops in 90 to 95% of people taking opioids long-term. Since tolerance to this problem does not generally develop, most people on long-term opioids need to take

913-495: Is a peripherally selective opioid available without a prescription used to suppress diarrhea. The ability to suppress diarrhea also produces constipation when opioids are used beyond several weeks. Naloxegol , a peripherally-selective opioid antagonist is now available to treat opioid induced constipation. Opioids may help with shortness of breath particularly in advanced diseases such as cancer and COPD among others. However, findings from two recent systematic reviews of

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996-561: Is a diminutive form of pupa , "girl". (The double meaning in Latin is preserved in English, where pupil means both "schoolchild" and "dark central portion of the eye within the iris".) This may be because the reflection of one's image in the pupil is a minuscule version of one's self. In the Old Babylonian period (c. 1800-1600 BC) in ancient Mesopotamia, the expression "protective spirit of the eye"

1079-508: Is a process characterized by neuroadaptations that result in reduced drug effects. While receptor upregulation may often play an important role other mechanisms are also known. Tolerance is more pronounced for some effects than for others; tolerance occurs slowly to the effects on mood, itching, urinary retention, and respiratory depression, but occurs more quickly to the analgesia and other physical side effects. However, tolerance does not develop to constipation or miosis (the constriction of

1162-470: Is actually the color of one's iris, the cornea being transparent and the white sclera entirely outside the area of interest. Melanin is yellowish to dark hazel in the stromal pigment cells, and black in the iris pigment epithelium , which lies in a thin but very opaque layer across the back of the iris. Most human irises also show a condensation of the brownish stromal melanin in the thin anterior border layer, which by its position has an overt influence on

1245-539: Is associated with increased adverse effects such as "sedation, nausea, vomiting, constipation, urinary retention, and falls". As a result, older adults taking opioids are at greater risk for injury. Opioids do not cause any specific organ toxicity, unlike many other drugs, such as aspirin and paracetamol. They are not associated with upper gastrointestinal bleeding and kidney toxicity . Prescription of opioids for acute low back pain and management of osteoarthritis seem to have long-term adverse effects According to

1328-547: Is attested, perhaps arising from the same phenomenon. The English phrase apple of my eye arises from an Old English usage, in which the word apple meant not only the fruit but also the pupil or eyeball. Iris (anatomy) The word "iris" is derived from the Greek word for " rainbow ", also its goddess plus messenger of the gods in the Iliad , because of the many colours of this eye part. The iris consists of two layers:

1411-442: Is better treated with medications other than opioids. Paracetamol and nonsteroidal anti-inflammatory drugs including ibuprofen and naproxen are considered safer alternatives. They are frequently used combined with opioids, such as paracetamol combined with oxycodone ( Percocet ) and ibuprofen combined with hydrocodone ( Vicoprofen ), which boosts the pain relief but is also intended to deter recreational use. Codeine

1494-487: Is closely related to the same mechanism as tolerance. While there is anecdotal claims of benefit with ibogaine , data to support its use in substance dependence is poor. Critical patients who received regular doses of opioids experience iatrogenic withdrawal as a frequent syndrome. Drug addiction is a complex set of behaviors typically associated with misuse of certain drugs, developing over time and with higher drug dosages. Addiction includes psychological compulsion, to

1577-428: Is due to gastric stasis (large volume vomiting, brief nausea relieved by vomiting, oesophageal reflux, epigastric fullness, early satiation), besides direct action on the chemoreceptor trigger zone of the area postrema , the vomiting centre of the brain. Vomiting can thus be prevented by prokinetic agents ( e.g. domperidone or metoclopramide ). If vomiting has already started, these drugs need to be administered by

1660-485: Is generally discouraged where that is the case. The weak opioid codeine , in low doses and combined with one or more other drugs, is commonly available in prescription medicines and without a prescription to treat mild pain. Other opioids are usually reserved for the relief of moderate to severe pain. Opioids are effective for the treatment of acute pain (such as pain following surgery). For immediate relief of moderate to severe acute pain, opioids are frequently

1743-523: Is not necessary, so it is chiefly concerned with admitting sufficient light into the eye. When bright light is shone on the eye, light-sensitive cells in the retina, including rod and cone photoreceptors and melanopsin ganglion cells , will send signals to the oculomotor nerve , specifically the parasympathetic part coming from the Edinger-Westphal nucleus , which terminates on the circular iris sphincter muscle. When this muscle contracts, it reduces

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1826-406: Is not otherwise dangerous. The size of the pupil (often measured as diameter ) can be a symptom of an underlying disease. Dilation of the pupil is known as mydriasis and contraction as miosis . Not all variations in size are indicative of disease however. In addition to dilation and contraction caused by light and darkness, it has been shown that solving simple multiplication problems affects

1909-501: Is now rarely used. A related drug, prochlorperazine is more often used, although it has similar risks. Stronger antiemetics such as ondansetron or tropisetron are sometimes used when nausea is severe or continuous and disturbing, despite their greater cost. A less expensive alternative is dopamine antagonists such as domperidone and metoclopramide. Domperidone does not cross the blood–brain barrier and produce adverse central antidopaminergic effects, but blocks opioid emetic action in

1992-501: Is properly limited to the natural alkaloids found in the resin of the opium poppy although some include semi-synthetic derivatives. Narcotic , derived from words meaning 'numbness' or 'sleep', as an American legal term, refers to cocaine and opioids, and their source materials; it is also loosely applied to any illegal or controlled psychoactive drug. In some jurisdictions all controlled drugs are legally classified as narcotics . The term can have pejorative connotations and its use

2075-415: Is seen; if not, they will remain blue or gray. All the contributing factors towards eye color and its variation are not fully understood. Autosomal recessive/dominant traits in iris color are inherent in other species, but coloration can follow a different pattern. Heterochromia (also known as a heterochromia iridis or heterochromia iridum) is an ocular condition in which one iris is a different color from

2158-402: Is that a partially constricted circular pupil shades the peripheral zones of the lens which would lead to poorly focused images at relevant wavelengths. The vertical slit pupil allows for use of all wavelengths across the full diameter of the lens, even in bright light. It has also been suggested that in ambush predators such as some snakes, vertical slit pupils may aid in camouflage, breaking up

2241-412: Is uncertain. Opioids are contraindicated as a first-line treatment for headache because they impair alertness, bring risk of dependence, and increase the risk that episodic headaches will become chronic. Opioids can also cause heightened sensitivity to headache pain. When other treatments fail or are unavailable, opioids may be appropriate for treating headache if the patient can be monitored to prevent

2324-631: The Siberian tiger (Panthera tigris altaica) has circular pupils and the Eurasian lynx (Lynx lynx) is intermediate between those of the domestic cat and the Siberian tiger. A similar difference between small and large species may be present in canines. The small red fox (Vulpes vulpes) has vertical slit pupils whereas their large relatives, the gray wolf (Canis lupus lupus) and domestic dogs (Canis lupus familiaris) have round pupils. One explanation for

2407-509: The USCDC , methadone was involved in 31% of opioid related deaths in the US between 1999–2010 and 40% as the sole drug involved, far higher than other opioids. Studies of long term opioids have found that many stop them, and that minor side effects were common. Addiction occurred in about 0.3%. In the United States in 2016 opioid overdose resulted in the death of 1.7 in 10,000 people. Tolerance

2490-406: The aqueous humour constantly drains out of the eye, with the result that diseases of the iris often have important effects on intraocular pressure and indirectly on vision. The iris along with the anterior ciliary body provide a secondary pathway for aqueous humour to drain from the eye. The iris is divided into two major regions: The collarette is the thickest region of the iris, separating

2573-425: The central and peripheral nervous system and the gastrointestinal tract . These receptors mediate both the psychoactive and the somatic effects of opioids. Opioid drugs include partial agonists , like the anti-diarrhea drug loperamide and antagonists like naloxegol for opioid-induced constipation, which do not cross the blood–brain barrier , but can displace other opioids from binding to those receptors in

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2656-546: The chemoreceptor trigger zone . This drug is not available in the U.S. Some antihistamines with anticholinergic properties (e.g. orphenadrine , diphenhydramine ) may also be effective. The first-generation antihistamine hydroxyzine is very commonly used, with the added advantages of not causing movement disorders, and also possessing analgesic-sparing properties. Δ - tetrahydrocannabinol relieves nausea and vomiting; it also produces analgesia that may allow lower doses of opioids with reduced nausea and vomiting. Vomiting

2739-435: The evolution of slit pupils is that they can exclude light more effectively than a circular pupil. This would explain why slit pupils tend to be found in the eyes of animals with a crepuscular or nocturnal lifestyle that need to protect their eyes during daylight. Constriction of a circular pupil (by a ring-shaped muscle) is less complete than closure of a slit pupil, which uses two additional muscles that laterally compress

2822-1093: The myenteric plexus . Because opioids are addictive and may result in fatal overdose, most are controlled substances . In 2013, between 28 and 38 million people used opioids illicitly (0.6% to 0.8% of the global population between the ages of 15 and 65). In 2011, an estimated 4 million people in the United States used opioids recreationally or were dependent on them. As of 2015, increased rates of recreational use and addiction are attributed to over-prescription of opioid medications and inexpensive illicit heroin . Conversely, fears about overprescribing, exaggerated side effects, and addiction from opioids are similarly blamed for under-treatment of pain. Opioids include opiates , an older term that refers to such drugs derived from opium , including morphine itself. Other opioids are semi-synthetic and synthetic drugs such as hydrocodone , oxycodone , and fentanyl ; antagonist drugs such as naloxone ; and endogenous peptides such as endorphins . The terms opiate and narcotic are sometimes encountered as synonyms for opioid. Opiate

2905-857: The opium poppy plant. Opioids work in the brain to produce a variety of effects, including pain relief. As a class of substances, they act on opioid receptors to produce morphine -like effects. The terms 'opioid' and 'opiate' are sometimes used interchangeably, but there are key differences based on the manufacturing processes of these medications. Medically they are primarily used for pain relief , including anesthesia . Other medical uses include suppression of diarrhea , replacement therapy for opioid use disorder , reversing opioid overdose , and suppressing cough . Extremely potent opioids such as carfentanil are approved only for veterinary use. Opioids are also frequently used recreationally for their euphoric effects or to prevent withdrawal . Opioids can cause death and have been used for executions in

2988-529: The First was dubbed dikoros (having two irises) for his patent heterochromia since his right iris had a darker color than the left one. In contrast, heterochromia and variegated iris patterns are common in veterinary practice. Siberian Husky dogs show heterochromia, possibly analogous to the genetically determined Waardenburg syndrome of humans. Some white cat fancies (e.g., white Turkish Angora or white Turkish Van cats) may show striking heterochromia, with

3071-716: The United States . Side effects of opioids may include itchiness , sedation , nausea , respiratory depression , constipation , and euphoria . Long-term use can cause tolerance , meaning that increased doses are required to achieve the same effect, and physical dependence , meaning that abruptly discontinuing the drug leads to unpleasant withdrawal symptoms. The euphoria attracts recreational use, and frequent, escalating recreational use of opioids typically results in addiction. An overdose or concurrent use with other depressant drugs like benzodiazepines commonly results in death from respiratory depression . Opioids act by binding to opioid receptors, which are found principally in

3154-581: The ability to manipulate the size of their pupils (i.e. dilating and constricting them) on command, without any changes in lighting condition or eye accommodation state. However, this ability is likely very rare and its purpose or advantages over those without it are unclear. Not all animals have circular pupils. Some have slits or ovals which may be oriented vertically, as in crocodiles , vipers , cats and foxes , or horizontally as in some rays , flying frogs , mongooses and artiodactyls such as elk , red deer , reindeer and hippopotamus , as well as

3237-403: The average pupil size decreases, though not at a steady rate. At this stage the pupils do not remain completely still, therefore may lead to oscillation, which may intensify and become known as hippus . The constriction of the pupil and near vision are closely tied. In bright light, the pupils constrict to prevent aberrations of light rays and thus attain their expected acuity; in the dark, this

3320-475: The benefits and harms should be reassessed at least every three months. In treating chronic pain, opioids are an option to be tried after other less risky pain relievers have been considered, including paracetamol or NSAIDs like ibuprofen or naproxen . Some types of chronic pain, including the pain caused by fibromyalgia or migraine , are preferentially treated with drugs other than opioids. The efficacy of using opioids to lessen chronic neuropathic pain

3403-619: The blood vessels, collagen in the vessel and stroma) is the most important element. Rayleigh scattering and Tyndall scattering , (which also happen in the sky) and diffraction also occur. Raman scattering , and constructive interference , as in the feathers of birds, do not contribute to the color of the eye, but interference phenomena are important in the brilliantly colored iris pigment cells ( iridophores ) in many animals. Interference effects can occur at both molecular and light-microscopic scales, and are often associated (in melanin-bearing cells) with quasicrystalline formations, which enhance

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3486-534: The circular outline of the eye. In a study of Australian snakes , pupil shapes correlated both with diel activity times and with foraging behavior. Most snake species with vertical pupils were nocturnal and also ambush foragers, and most snakes with circular pupils were diurnal and active foragers. Overall, foraging behaviour predicted pupil shape accurately in more cases than did diel time of activity, because many active-foraging snakes with circular pupils were not diurnal. It has been suggested that there may be

3569-418: The color of the iris is due to a lack of pigmentation, as in the pinkish-white of oculocutaneous albinism , or to obscuration of its pigment by blood vessels, as in the red of an abnormally vascularised iris. Despite the wide range of colors, the only pigment that contributes substantially to normal iris color is the dark pigment melanin . The quantity of melanin pigment in the iris is one factor in determining

3652-529: The development of chronic headache. Opioids are being used more frequently in the management of non-malignant chronic pain . This practice has now led to a new and growing problem with addiction and misuse of opioids. Because of various negative effects the use of opioids for long-term management of chronic pain is not indicated unless other less risky pain relievers have been found ineffective. Chronic pain which occurs only periodically, such as that from nerve pain , migraines , and fibromyalgia , frequently

3735-451: The dilator is inhibited. The reverse is true, so control of pupil size is controlled by differences in contraction intensity of each muscle. Another term for the constriction of the pupil is miosis . Substances that cause miosis are described as miotic. Dilation of the pupil is mydriasis . Dilation can be caused by mydriatic substances such as an eye drop solution containing tropicamide . A condition called bene dilitatism occurs when

3818-418: The dilator muscles. The high pigment content blocks light from passing through the iris to the retina, restricting it to the pupil. The outer edge of the iris, known as the root, is attached to the sclera and the anterior ciliary body . The iris and ciliary body together are known as the anterior uvea . Just in front of the root of the iris is the region referred to as the trabecular meshwork , through which

3901-436: The dilator pupillae. The pupil's diameter, and thus the inner border of the iris, changes size when constricting or dilating. The outer border of the iris does not change size. The constricting muscle is located on the inner border. The back surface is covered by a heavily pigmented epithelial layer that is two cells thick (the iris pigment epithelium), but the front surface has no epithelium. This anterior surface projects as

3984-717: The domestic horse . Goats , sheep , toads and octopus pupils tend to be horizontal and rectangular with rounded corners. Some skates and rays have crescent shaped pupils, gecko pupils range from circular, to a slit, to a series of pinholes, and the cuttlefish pupil is a smoothly curving W shape. Although human pupils are normally circular, abnormalities like colobomas can result in unusual pupil shapes, such as teardrop, keyhole or oval pupil shapes. There may be differences in pupil shape even between closely related animals. In felids, there are differences between small- and large eyed species. The domestic cat (Felis sylvestris domesticus) has vertical slit pupils, its large relative

4067-513: The dose is reduced abruptly or, specifically in the case of opioids, when an antagonist ( e.g. , naloxone ) or an agonist-antagonist ( e.g. , pentazocine ) is administered. Physical dependence is a normal and expected aspect of certain medications and does not necessarily imply that the patient is addicted. The withdrawal symptoms for opiates may include severe dysphoria , craving for another opiate dose, irritability, sweating , nausea , rhinorrea , tremor , vomiting and myalgia . Slowly reducing

4150-506: The effect in one eye to carry over to the other. The pupil gets wider in the dark and narrower in light. When narrow, the diameter is 2 to 4 millimeters. In the dark it will be the same at first, but will approach the maximum distance for a wide pupil 3 to 8 mm. However, in any human age group there is considerable variation in maximal pupil size. For example, at the peak age of 15, the dark-adapted pupil can vary from 4 mm to 9 mm with different individuals. After 25 years of age,

4233-547: The efficacy and safety of these types of preparations. Further tamper resistant medications are currently under consideration with trials for market approval by the FDA. The amount of evidence available only permits making a weak conclusion, but it suggests that a physician properly managing opioid use in patients with no history of substance use disorder can give long-term pain relief with little risk of developing addiction, or other serious side effects. Problems with opioids include

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4316-417: The extent that the affected person persists in actions leading to dangerous or unhealthy outcomes. Opioid addiction includes insufflation or injection, rather than taking opioids orally as prescribed for medical reasons. In European nations such as Austria, Bulgaria, and Slovakia, slow-release oral morphine formulations are used in opiate substitution therapy (OST) for patients who do not well tolerate

4399-406: The field of view and image quality of horizontal contours. They further explained why elongated pupils are correlated with the animal's height. The pupil plays a role in eye contact and nonverbal communication . The voluntary or involuntary enlargement or dilation of the pupils indicates cognitive arousal , interest in the subject of attention, and/or sexual arousal . On the other hand, when

4482-436: The following: All of the opioids can cause side effects. Common adverse reactions in patients taking opioids for pain relief include nausea and vomiting, drowsiness , itching, dry mouth, dizziness , and constipation . Tolerance to nausea occurs within 7–10 days, during which antiemetics ( e.g. low dose haloperidol once at night) are very effective. Due to severe side effects such as tardive dyskinesia, haloperidol

4565-411: The front pigmented fibrovascular layer known as a stroma and, behind the stroma, pigmented epithelial cells. The stroma is connected to a sphincter muscle ( sphincter pupillae ), which contracts the pupil in a circular motion, and a set of dilator muscles ( dilator pupillae ), which pull the iris radially to enlarge the pupil, pulling it in folds. The sphincter pupillae is the opposing muscle of

4648-536: The intake of opioids over days and weeks can reduce or eliminate the withdrawal symptoms. The speed and severity of withdrawal depends on the half-life of the opioid; heroin and morphine withdrawal occur more quickly than methadone withdrawal. The acute withdrawal phase is often followed by a protracted phase of depression and insomnia that can last for months. The symptoms of opioid withdrawal can be treated with other medications, such as clonidine . Physical dependence does not predict drug misuse or true addiction, and

4731-399: The iris is the aperture stop . The image of the pupil as seen from outside the eye is the entrance pupil , which does not exactly correspond to the location and size of the physical pupil because it is magnified by the cornea . On the inner edge lies a prominent structure, the collarette , marking the junction of the embryonic pupillary membrane covering the embryonic pupil. The iris is

4814-616: The literature found that opioids were not necessarily more effective in treating shortness of breath in patients who have advanced cancer. Though not typically a first line of treatment, opioids, such as oxycodone and methadone , are sometimes used in the treatment of severe and refractory restless legs syndrome . Hyperalgesia Opioid-induced hyperalgesia (OIH) has been evident in patients after chronic opioid exposure. Common and short term Other Each year 69,000 people worldwide die of opioid overdose, and 15 million people have an opioid addiction. In older adults, opioid use

4897-452: The most common pattern being one uniformly blue, the other copper, orange, yellow, or green. Striking variation within the same iris is also common in some animals, and is the norm in some species. Several herding breeds, particularly those with a blue merle coat color (such as Australian Shepherds and Border Collies ) may show well-defined blue areas within a brown iris, as well as separate blue and darker eyes. Some horses (usually within

4980-417: The most significant being the amount of light in the environment. The term "pupil" was coined by Gerard of Cremona . In humans, the pupil is circular, but its shape varies between species; some cats , reptiles , and foxes have vertical slit pupils, goats and sheep have horizontally oriented pupils, and some catfish have annular types. In optical terms, the anatomical pupil is the eye's aperture and

5063-471: The most suitable drug for a particular patient. Otherwise, treatment with CNS stimulants is generally effective. Itching tends not to be a severe problem when opioids are used for pain relief, but antihistamines are useful for counteracting itching when it occurs. Non-sedating antihistamines such as fexofenadine are often preferred as they avoid increasing opioid induced drowsiness. However, some sedating antihistamines such as orphenadrine can produce

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5146-545: The optic nerves are partially damaged. This condition is typified by chronically widened pupils due to the decreased ability of the optic nerves to respond to light. In normal lighting, people affected by this condition normally have dilated pupils, and bright lighting can cause pain. At the other end of the spectrum, people with this condition have trouble seeing in darkness. It is necessary for these people to be especially careful when driving at night due to their inability to see objects in their full perspective. This condition

5229-446: The optical effects. Interference is recognised by characteristic dependence of color on the angle of view, as seen in eyespots of some butterfly wings , although the chemical components remain the same. White babies are usually born blue-eyed since no pigment is in the stroma, and their eyes appear blue due to scattering and selective absorption from the posterior epithelium. If melanin is deposited substantially, brown or black color

5312-410: The other iris (complete heterochromia), or where the part of one iris is a different color from the remainder (partial heterochromia or sectoral heterochromia). Uncommon in humans, it is often an indicator of ocular disease, such as chronic iritis or diffuse iris melanoma, but may also occur as a normal variant. Sectors or patches of strikingly different colors in the same iris are less common. Anastasius

5395-414: The other stromal components. Sometimes, lipofuscin , a yellow "wear and tear" pigment, also enters into the visible eye color, especially in aged or diseased green eyes. The optical mechanisms by which the nonpigmented stromal components influence eye color are complex, and many erroneous statements exist in the literature. Simple selective absorption and reflection by biological molecules ( hemoglobin in

5478-510: The overall color. The degree of dispersion of the melanin, which is in subcellular bundles called melanosomes , has some influence on the observed color, but melanosomes in the iris of humans and other vertebrates are not mobile, and the degree of pigment dispersion cannot be reversed. Abnormal clumping of melanosomes does occur in disease and may lead to irreversible changes in iris color (see heterochromia , below). Colors other than brown or black are due to selective reflection and absorption from

5561-413: The phenotypic eye color of an organism. Structurally, this huge molecule is only slightly different from its equivalent found in skin and hair . Iris color is due to variable amounts of eumelanin (brown/black melanins) and pheomelanin (red/yellow melanins) produced by melanocytes. More of the former is found in brown-eyed people and of the latter in blue- and green-eyed people. The limbal ring appears as

5644-467: The pupil is voluntarily or involuntarily contracted , it could indicate the opposite - disinterest or disgust. Exceptionally large or dilated pupils are also perceived to be an attractive feature in body language. In a surprising number of unrelated languages, the etymological meaning of the term for pupil is "little person". This is true, for example, of the word pupil itself: this comes into English from Latin pūpilla , which means "doll, girl", and

5727-425: The pupil of the eye to less than or equal to two millimeters). This idea has been challenged, however, with some authors arguing that tolerance does develop to miosis. Tolerance to opioids is attenuated by a number of substances, including: Tolerance is a physiologic process where the body adjusts to a medication that is frequently present, usually requiring higher doses of the same medication over time to achieve

5810-436: The pupil. Certain drugs cause constriction of the pupils, such as opioids . Other drugs, such as atropine , LSD , MDMA , mescaline , psilocybin mushrooms , cocaine and amphetamines may cause pupil dilation. The sphincter muscle has a parasympathetic innervation, and the dilator has a sympathetic innervation. In pupillary constriction induced by pilocarpine, not only is the sphincter nerve supply activated but that of

5893-399: The pupil. For example, the cat's slit pupil can change the light intensity on the retina 135-fold compared to 10-fold in humans. However, this explanation does not account for circular pupils that can be closed to a very small size (e.g., 0.5 mm in the tarsier ) and the rectangular pupils of many ungulates which do not close to a narrow slit in bright light. An alternative explanation

5976-536: The pupillary portion from the ciliary portion. The collarette is a vestige of the coating of the embryonic pupil. It is typically defined as the region where the sphincter muscle and dilator muscle overlap. Radial ridges extend from the periphery to the pupillary zone, to supply the iris with blood vessels. The root of the iris is the thinnest and most peripheral. The muscle cells of the iris are smooth muscle in mammals and amphibians, but are striated muscle in reptiles (including birds). Many fish have neither, and, as

6059-451: The pupils when accommodation is initiated, to increase the depth of field . Very few humans possess the ability to exert direct voluntary control over their iris muscles, which grants them the ability to dilate and constrict their pupils on command. However, there is no clear purpose or advantage to this. The iris is usually strongly pigmented , with the color typically ranging between brown, hazel, green, gray, and blue. Occasionally,

6142-399: The same effect. It is a common occurrence in individuals taking high doses of opioids for extended periods, but does not predict any relationship to misuse or addiction. Physical dependence is the physiological adaptation of the body to the presence of a substance, in this case opioid medication. It is defined by the development of withdrawal symptoms when the substance is discontinued, when

6225-529: The side effects of buprenorphine or methadone . Buprenorphine can also be used together with naloxone for a longer treatment of addiction. In other European countries including the UK, this is also legally used for OST although on a varying scale of acceptance. Slow-release formulations of medications are intended to curb misuse and lower addiction rates while trying to still provide legitimate pain relief and ease of use to pain patients. Questions remain, however, about

6308-465: The size of the pupil by means of contracting the iris sphincter muscle and/or the iris dilator muscle . The size of the pupils is dependent on many factors (including light, emotional state, cognitive load, arousal, stimulation), and can range from less than 2 mm in diameter, to as large as 9 mm in diameter. However, there is considerable variation in maximal pupil diameter by individual humans, and decreases with age. The irises also contract

6391-442: The size of the pupil. This is the pupillary light reflex , which is an important test of brainstem function. Furthermore, the pupil will dilate if a person sees an object of interest. If the drug pilocarpine is administered, the pupils will constrict and accommodation is increased due to the parasympathetic action on the circular muscle fibers, conversely, atropine will cause paralysis of accommodation (cycloplegia) and dilation of

6474-607: The size of the pupil. The simple act of recollection can dilate the size of the pupil, however when the brain is required to process at a rate above its maximum capacity, the pupils contract. There is also evidence that pupil size is related to the extent of positive or negative emotional arousal experienced by a person. Myopic individuals have larger resting and dark dilated pupils than hyperopic and emmetropic individuals, likely due to requiring less accommodation (which results in pupil constriction). Some humans are able to exert direct control over their iris muscles, giving them

6557-453: The sphincter pupillae contract, the iris decreases or constricts the size of the pupil. The dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, cause the pupil to dilate when they contract. These muscles are sometimes referred to as intrinsic eye muscles. The sensory pathway (rod or cone, bipolar, ganglion) is linked with its counterpart in the other eye by a partial crossover of each eye's fibers. This causes

6640-435: The treatment of acute cough does not recommend its use. (The opioid analogue dextromethorphan , long claimed to be as effective a cough suppressant as codeine, has similarly demonstrated little benefit in several recent studies. ) Low dose morphine may help chronic cough but its use is limited by side effects. In cases of diarrhea-predominate irritable bowel syndrome , opioids may be used to suppress diarrhea. Loperamide

6723-509: The treatment of choice due to their rapid onset, efficacy and reduced risk of dependence. However, a new report showed a clear risk of prolonged opioid use when opioid analgesics are initiated for an acute pain management following surgery or trauma. They have also been found to be important in palliative care to help with the severe, chronic, disabling pain that may occur in some terminal conditions such as cancer, and degenerative conditions such as rheumatoid arthritis . In many cases opioids are

6806-446: The white, spotted, palomino, or cremello groups of breeds) may show amber, brown, white and blue all within the same eye, without any sign of eye disease. One eye with a white or bluish-white iris is also known as a "walleye". Iridology (also known as iridodiagnosis) is an alternative medicine technique whose proponents believe that patterns, colors, and other characteristics of the iris can be examined to determine information about

6889-424: Was once viewed as the "gold standard" in cough suppressants , but this position is now questioned. Some recent placebo -controlled trials have found that it may be no better than a placebo for some causes including acute cough in children. As a consequence, it is not recommended for children. Additionally, there is no evidence that hydrocodone is useful in children. Similarly, a 2012 Dutch guideline regarding

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