Chartered Portfolio Manager and Investment Management- week 3 Essay

Chartered Portfolio Manager and Investment Management- week 3 responses - Essay ExampleI agree that it is non suitable to add a hem in fund to such a clients portfolio who has low capital base, risk averse nature, and willingness for long-term returns. scorn the accessibility of general public to the hedge funds as a result of their inclusion in mutual funds, they are not a viable option because of their cost and subjectivity of information. Participation in returns is not likely to increase considering the current limitations of the hedge funds.You have provided a concise definition of hedge funds. This was a particularly informative post as it introduced some new concepts such as derivatives and the investment technique of leverage. I dont forecast it is suitable to add hedge funds that use leverage to a clients portfolio given the enormity of risk of loss. I agree that institutions willingness for variegation drives them toward hedge funds. However, a fair understanding of ri sk and its comparison to the capital base is fundamental to making informed

What factors influence policies and practices of multinational firms Essay

What factors influence policies and practices of multinational firms Discuss - Essay ExampleTo initiate and embody the entry, MNCs have to set targets and formulate various strategies according to the situation prevailing in those foreign markets. While formulating the strategies, the organizations leader and the management team will for the first time look at the factors that may aid them to make a successful entry. After analyzing the positive factors, the firms will or should have to analyze the negative factors or challenges that may impede its entry. As every foreign market or country will have different political, social, economic conditions as well as different customers, competitors, prospective employees, etc, etc, there will be umpteen challenges, which will block the firms success. Thus, both these factors could influence the practices and policies of MNCs particularly in its foreign operations.Among the umpteen economic based movements, globalisation is the one which h ad and is still having major impact on the economic development of many countries and its people worldwide. The word globalisation tag a set of transitions in the global political economy since the 1970s, in which multinational forms of capitalist organization began to be replaced by transnational (Appadurai, cited in Meyer and Geschiere 1999). scotch part of globalisation is the key because with the whole world becoming a kind of global village, barriers between the countries are broken with integration happening chiefly in the economic aspects. In this scenario, foreign organizations particularly MNCs, using the globalisation plank, have entered and will also enter various sectors of the businesses leading to the establishment of many industries.With these MNCs providing good employment and the resultant good development, people of those countries have became financially stable and are going in search of material comforts, causing impacts on social change. For a

Plato's view of immortality Essay Example | Topics and Well Written Essays - 1250 words

Platos view of immortality - Essay Examplelato believes that only a soul of a philosophical lover of knowledge and virtue is righteous of traveling beyond the process of rebirth to ultimate fulfillment. Plato believed in the immortality of the soul and the overall. Plato believed that the body played no real role in who we be as people the only thing that shows who we are is our soul. Plato even suggests that death could be like an eternal sleep, where none of the senses are active. However, Plato says that it would be better to travel to a place where one could converse with all the great thinkers of the past. Plato argues that our soul is immortal because we are born with some form of intelligence within us. He argues that since things are supposedly born from opposites, life can only be birthed from death.Plato, RepublicPlato denies that fever, or any other disease, or the knife put to the throat, or even the acrid up of the whole body into the minutest pieces, can destroy the soul, until she herself is proved to become more unholy or unrighteous in consequence of these things being through with(p) to the body but that the soul, or anything else if not destroyed by an internal evil, can be destroyed by an external one, is not to be confirm by any man.Plato, Republic Soul cannot be destroyed by an evil whether inherent or external, essential exist forever, and if exists forever is immortal.Plato, in Republic asserts that the immortality is show by the previous argument, and there are many other proofs but to see it as what it really is, not as we now behold it, deflower by communion with the body and other miseries, you must contemplate it with the eye of reason, in its original purity and then beauty will be revealed, and arbiter and injustice and all the things which we have described will be manifested more clearly. Thus far, we have spoken the truth concerning as it appears at present, but we must remember also that we have seen it only in a condit ion which may be compared to that of the sea-god,

Business Environment Analysis of British Airways Essay - 1

Business Environment Analysis of British Airways - Essay ExampleThe assessment of the external environment is conducted in reference to its dissemble on British Airways. For the purpose, the range of strategic management tools has been employed.British Airways (BA) is a private limited company is renowned airline that has recently celebrated 90 years of existence in the year 2009. It is one the leading premium airlines of the world and the largest airline of UK and covers around 400 destinations across the world (British Airways, 2013). The business mannequin of BA is based on the revenue generation from the passenger as well as cargo delivery aids. With the long rich history and experience, BA has become one of the leading airlines that have extensive scheduled flights and network of airline. Additionally, it is a comprehensive list of joint agreements, franchise partners and other defined codes that enables it to service wide network of stations (airports). Importantly, in the year 2010, BA merged into Iberia which is the largest airline of Spain (British Airways, n.d.).British Airways generate its revenue from the two basic sources including passenger revenue and the cargo revenue. For the year 2013, BA generated revenue of around 10,129 million from the passenger revenue with the growth of 6.6% while the cargo revenue declined by 6.5% and generated 689 million in 2013 as compared to 2012. The year 2013 was driven by considerable investment in the airline with constant focus on expanding customer base along with the bell reduction measure at effect (British Airways, 2013).This section of the report will produce the information related to the British Airways. The information will be peculiar(prenominal) to the business direction and future vision of the business along with impact of the external environment on BA and its response.The mission of British Airways, as describe in the marketing in magazine, is to serve (Eleftheriou-Smith, 2011).

Critique of Research Studies Assignment Example | Topics and Well Written Essays - 2250 words

Critique of Research Studies - Assignment ExampleThe police detective introduces the scope of the research by stating that all health c be workers are required to comply with hand-hygiene guidelines and provides the rational for this practice and thus, the study. However, the researcher does not provide an outline of how the issues relating to compliance are going to be addressed within the report.Creedon (2006) states the of import research problem as the health care workers observance of the hand-hygiene rules during patient care in an ICU in Ireland before and after execution of a multilateral hand-hygiene program, in addition to the attitudes, knowledge, and beliefs of health workers in relation to the hand-hygiene program.The researcher is very precise in stating the research caputs relating to this particular study. The first research question relates to what effects the multifaceted approach would have on the compliance to hand washing guidelines by health care workers. Ad ditionally Creedon (2006) questions the effects that a multifaceted hand-hygiene program might have on the beliefs, knowledge, and attitudes of health care workers.The literature review has been arranged in a logical order. The researcher has gone from the familiar idea of how hand washing relates to infection, to giving data on how many persons are affected and the costs of treatment. However, the review is not balanced as the researcher only focuses on the reasons and consequences of non-compliance, without giving information existing compliance rates. Additionally, most of the reviewed materials are relatively old, with some being published in the 1980s.The research identifies its suppositious framework as lifting the standards of health interventions by encouraging behavioral change among health care professionals (Creedon, 2006). However, although the framework is appropriate for this study, it does not provide an adequate definition of how the behavior change will be implem ented in order

Smile Now, Cry Later Essay Example for Free

Smile Now, Cry Later EssayGangs ar decent a growing problem within American society. In 2002 more than 877,700 young people between the age of 10 to 24 were injured from risky acts, and 79% of homicide victims ages 10 to 24 were killed with firearms (Youth Violence Fact Sheet 3). Young people are turning to gangs as a way to solve problems in their lives, problems such as poverty, home violence, peer pressure, forced them to seek for power, money, respect, protection or simply love on the streets.the majority of gang members have been clear or have suffered violence in their homes. When youths join gangs, social activities with friends, and school. Gang members tend to fall behind their classmates in school and do not testify to stick around. They lost their motivation, interests and see school like a part of the problem and not like a solution. The majority of gang members are unknowledgeable because they drop out of school at a very young age.Most of them have or are rel ated with drugs, which destroy their lives and their chances for a proficient education and better life. Teenagers are joining gangs every day, becoming a problem in ghettos, urban areas and neighborhoods. They can be found in closely every city in the United States. One thing that all the gangs have in common is that According to Luis J. Rodriguezs book, Always Running La Vida Loca or The Crazy Life, the barrio gang experience, originated with the Mexican Pachuco gangs of the 1930s and 1940s and was later recreated with the cholos (5).The cholos, one of the most prominent and violent gangs in southern calcium region, still attract more and more teenagers. Teens usually join gangs in an attempt to correct both the social and emotional problems in their lives. There are many complex reasons kids join gangs the majority grew up in broken families without a father or a mother to look up to when everything went hugger-mugger and family conflicts present. These kids have a very low-se lf esteem due to the poor family function. They join in order to find love and acceptance.They see gangs as a surrogate, or substitute family, and they find in the streets what they dont have at home. They also join gangs to gain power, money and respect eventually by acquire into fights and killing each other. They often join gangs because they want to feel that they fit in somewhere, feeling rejected in more common situations due to their pagan heritage, religious believes, sex, or race. They join gangs as a way to protect themselves from discrimination, racism, prejudice, and to find acceptance among other members of the gang.Gangs are one of the results of urban deterioration thats why we see some communities more affected than others. Gangs are a violent reality that people have to deal with today because gangs are a direct result of human beings personal wants and peer pressure. These issues can be identify by looking at the way humans are influenced in society, because I tr uly believe there is good evidence to point the blame at several institutions including the power that the media has in our society, the government, drugs and our economic system.

Physics Project Essay Example for Free

Physics Project Essay nerve atomic number 18 organs that principal(prenominal)tain go down, and switch over it to electro-chemical impulses in neurons. The elementaryst photoreceptors in conscious mental imagery connect escaped to movement. In towering beings the nub is a complex optical system which collects light from the surrounding environment regulates its in xsity through a diaphragm focuses it through an adjustable assembly of lens systemes to frame an image converts this image into a set of electric signals and transmits these signals to the brain, through complex neural pathways that connect the heart, via the optic nerve, to the visual cortex and different argonas of the brain. Eyes with resolving power bring on come in ten fundamentally variant forms, and 96% of animal species take in a complex optical system.1 Image-resolving mid functions atomic number 18 present in molluscs, chordates and arthropods.2 The simplest look, such(prenominal) as tho se in microorganisms, do nonhing scarcely retrieve whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. From to a greater extent than complex look, retinal photosensitive ganglion cells delight signals along the retinohypothalamic tr enactment to the suprachiasmatic nuclei to effect circadian adjustment. Contentshide * 1 Overview * 2 Evolution * 3 Types of center of attention * 3.1 Normal eyes * 3.2 Pit eyes * 3.2.1 orbiculate lensed eye * 3.2.2 Multiple lenses * 3.2.3 Refractive cornea * 3.2.4 Reflector eyes * 3.3 Compound eyes * 3.3.1 Apposition eyes * 3.3.2 Superposition eyes * 3.3.3 Parabolic superposition * 3.3.4 Other * 3.3.5 Nutrients of the eye * 4 Relationship to life takements * 5 Visual sharpness * 6 Perception of contorts * 7 Rods and c stars * 8 Pigmentation * 9 See uniformly * 10 References * 10.1 Notes * 10.2 Bibliography * 11 External links edit OverviewEye of the wisent, the European bison Complex e yes understructure distinguish shapes and colors. The visual playing fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception in other organisms, eyes are located so as to maximize the field of view, such as in rabbits and horses, which engender monocular vision. The first proto-eyes evolved among animals 600 jillion years ago, ab turn up the time of the Cambrian explosion.3 The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes defend evolved in 96% of animal species in six of the thirty-plus4 main phyla.1 In more or less(prenominal) vertebrates and some molluscs, the eye works by allowing light to enter and project onto a photosensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for color) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision.The visual signals ar e then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focalisation lens and often an iris the relaxing or tightening of the muscles around the iris change the coat of the pupil, thereby regulating the amount of light that enters the eye,5 and reducing aberrations when there is enough light.6 The eyes of nigh cephalopods, fish, amphibians and snakes hand fixed lens shapes, and focusing vision is achieved by telescoping the lenssimilar to how a camera focuses.7 Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, whitethorn give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). a few(prenominal) eyes project up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360-degree field of visio n.Compound eyes are very sensitive to exploit. Some arthropods, including many Strepsiptera, have intricate eyes of only if a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images. Possessing detailed hyperspectral color vision, the Mantis shrimp has been reported to have the worlds more or less complex color vision system.8 Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The morsel of lenses in such an eye varied, however some trilobites had only one, and some had thousands of lenses in one eye.In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different quality of simple eye (stemmata) which gives a rough image. Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which can non actually see in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight. In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to blur the infra-red light produced by the hot ventsin this way the bearers can spot hot springs and avoid being boiled alive.9 editEvolutionMain article Evolution of the eyeEvolution of the eyePhotoreception is phylogenetically very old, with various theories of phylogenesis.10 The common origin (monophyly) of all animal eyes is now tolerantly acce pted as fact. This is establish upon the shared anatomical and genetic features of all eyes that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 540 million years ago.111213 The majority of the advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true visualize would have touched off an arms race.14 Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye typesetters cases and subtypes developed in parallel. Eyes in various animals show adaption to their requirements. For example, birds of fertilize have often greater visual acuity than humans, and some can see ultraviolet light. The different forms of eye in, for example, vertebrates and mollusks are often cited as examples of parallel evolution, patronage their distant common ancestry. The very earliest eyes, called eyespots, were simple patches of photoreceptor protein in unicellular animals.In multicellular beings, multicellular eyespots evolved, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness they could distinguish light and dark, but not the direction of the lightsource.15 Through gradual change, as the eyespot depressed into a shallow cup shape, the ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify the source. The equal deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes.16 The thin overgrowth of transparent cells over the eyes aperture, before formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialize into a transparent humou r that optimized color filtering, blocked harmful radiation, change the eyes refractive index, and allowed functionality out slope of water.The transparent protective cells eventually split into two stages, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.17 The gap between tissue layers naturally formed a bioconvex shape, an optimally ensample structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens the cornea and iris. Separation of the forward layer again formed a humour, the aqueous humour. This increased refractive power and again eased circulatory problems. Formation of a nontransparent ring allowed more tune vessels, more circulation, and larger eye sizes.17 editTypes of eyeThere are ten different eye layoutsindeed every way of cap turing an image known to man, with the exceptions of whizz and Fresnel lenses. Eye types can be categorized into simple eyes, with one concave photoreceptive surface, and compound eyes, which comprise a number of individual lenses laid out on a convex surface.1 Note that simple does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behavior or environment. The only limitations specific to eye types are that of resolutionthe physics of compound eyes prevents them from achieving a resolution better than 1. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures.1 Eyes as well as hang into two groups on the basis of their photoreceptors cellular construction, with the photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomeric. These two groups are not monophyletic the cnidaria alike possess cilliated cells, 18 and some annelids possess bo th.19 editNormal eyesHuman eyes are examples of normal eyesSimple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates, cephalopods, annelids, crustacea and cubozoa.20 editPit eyesPit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eyespot, to allow the organism to deduce the angle of incoming light.1 Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of simple eye. They are small, comprising up to about nose candy cells covering about 100 m.1 The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.1 editSpherical lensed eyeThe resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur un iversal gas constant encounteredhence increasing the resolution obtainable.1 The most basic form, withal seen in some gastropods and annelids, consists of a lens of one refractive index. A far hastyer image can be obtained using materials with a high refractive index, decreasing to the edges this decreases the focal length and thus allows a sharp image to form on the retina.1 This also allows a larger aperture for a given over sharpness of image, allowing more light to enter the lens and a flatter lens, reducing spherical aberration.1 Such an inhomogeneous lens is necessary in roam for the focal length to drop from about 4 times the lens radius, to 2.5 radii.1Heterogeneous eyes have evolved at least eight times quaternary or more times in gastropods, once in the copepods, once in the annelids and once in the cephalopods.1 No aquatic organisms possess homogeneous lenses presumptively the evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly outgrown.1 This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimize the effect of eye motion term the animal moves, most such eyes have alter eye muscles.1 The ocelli of insects bear a simple lens, but their focal point always lies behind the retina consequently they can never form a sharp image.This capitulates the function of the eye. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field this fast response is further accelerated by the large nerve bundles which rush the information to the brain.21 Focusing the image would also cause the suns image to be focused on a few receptors, with the possibility of damage under the intense light shielding the receptors would block out some light and thus reduce their sensitivity.21 This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above).21 editMultiple lensesSome marine organisms bear more than one lens for instance the copepod Pontella has three. The outer has a parabolic surface, countering the effectuate of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilias eyes have two lenses, arranged like those in a telescope.1 Such arrangements are rare and poorly understood, but represent an interest election construction. An interesting use of multiple lenses is seen in some hunters such as eagles and jumping spiders, which have a refractive cornea (discussed next) these have a forbid lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.1 editRefractive corneaIn the eyes of most mammals, birds, reptiles, and most other terrestrial ve rtebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air, relieving the lens of the function of reducing the focal length. This has freed it up for fine adjustments of focus, allowing a very high resolution to be obtained.1 As with spherical lenses, the problem of spherical aberration caused by the lens can be countered either by using an inhomogeneous lens material, or by flattening the lens.1 Flattening the lens has a disadvantage the quality of vision is diminished away from the main line of focus, meaning that animals requiring all-round vision are detrimented. Such animals often display an inhomogeneous lens instead.1 As mentioned above, a refractive cornea is only usable out of water in water, there is no difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures which have returned to the waterpenguins and seals, for examplelose their refractive cornea and return to lens-base d vision. An alternative solution, borne by some divers, is to have a very strong cornea.1 editReflector eyesAn alternative to a lens is to line the in nerve of the eye with mirrors, and reflect the image to focus at a central point.1 The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out.1 Many small organisms such as rotifers, copeopods and platyhelminths use such organs, but these are too small to produce usable images.1 Some larger organisms, such as scallops, also use reflector eyes. The scallop Pecten has up to 100 millimeter-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive lenses.1 There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of guanine crystals.22 editCompound eyesAn image of a house fly compound eye surface by using Scanning Electron MicroscopeAnatomy of the compound eye of an insectArthropods such as this carpenter bee have compound eyesA compound eye may consist of thousands of individual photoreceptor units or ommatidia (ommatidium, singular). The image perceived is a cabal of inputs from the numerous ommatidia (individual eye units), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarization of light.23 Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained. This can only be countered by increasing lens size and number.To see with a resolution comparable to our simple eyes, humans would require compound eyes which would each reach the size of their head. Compound eyes fall into two groups apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image.24 Compound eyes are common in arthropods, and are also present in annelids and some bivalvedd molluscs.25 Compound eyes, in arthropods at least, grow at their margins by the addition of new ommatidia.26 expression of the ommatidia of apposition compound eyesedit Apposition eyesApposition eyes are the most common form of eye, and are presumably the ancestral form of compound eye. They are found in all arthropod groups, although they may have evolved more than once within this phylum.1 Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound head start point.1 (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.) Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information.The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium. In the other kind of apposition eye, found in the Strepsiptera, lenses are not fused to one another, and each forms an entire image these images are combined in the brain. This is called the schizochroal compound eye or the neural superposition eye. Because images are combined additively, this arrangement allows vision under lower light levels.1 editSuperposition eyesThe second type is named the superposition eye. The superposition eye is divided into three types the refracting, the reflecting and the parabolic superposition eye. The refracting superposition eye has a gap b etween the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This kind is used mostly by nocturnal insects. In the parabolic superposition compound eye type, seen in arthropods such as mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp, prawns, crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses. editParabolic superpositionThis eye type functions by refracting light, then using a parabolic mirror to focus the image it combines features of superposition and apposition eyes.9 editOtherThe compound eyes of a dragonfly close fliers like flies or honey bees, or prey-catching insects like praying mantis or dragonflies, have specialized zones of ommatidia organized into a fovea area which gives piercing vision. In the acute zone the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp Dioptromysis paucispinosa.The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialized retina. The resulting eye is a mixture of a simple eye within a compound eye. Another version is the pseudofaceted eye, a s seen in Scutigera. This type of eye consists of a cluster of numerous ocelli on each side of the head, organized in a way that resembles a true compound eye. The body of Ophiocoma wendtii, a type of brittle star, is covered with ommatidia, turning its whole discase into a compound eye. The same is true of many chitons. editNutrients of the eyeThe cilial body is triangular in prospecttal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly blushered, continuous with the retinal key epithelium, and constitutes the cells of the dilator muscle. The vitreous is the transparent, colorless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye.27 It is produced by certain retinal cells.It is of rather similar composition to the cornea, but cops very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs of the surface of the vitreous, which employ the hyaluronic acid), no blood vessels, and 98-99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibers with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye. editRelationship to life requirementsEyes are generally adapted to the environment and life requirements of the organism which bears them. For instance, the distribution of photoreceptors tends to match the area in which the highest acuity is required, with horizon-scanning organisms, such as those that live on the African plains, having a horizontal line of high-density ganglia, while tree-dwelling creatures which require good all-round vision tend to have a symmetrical distribution of gangl ia, with acuity decreasing outwards from the centre. Of course, for most eye types, it is impossible to variegate from a spherical form, so only the density of optical receptors can be altered. In organisms with compound eyes, it is the number of ommatidia rather than ganglia that reflects the region of highest data acquisition.123-4 opthalmic superposition eyes are constrained to a spherical shape, but other forms of compound eyes may deform to a shape where more ommatidia are aligned to, say, the horizon, without altering the size or density of individual ommatidia.28Eyes of horizon-scanning organisms have stalks so they can be easily aligned to the horizon when this is inclined, for example if the animal is on a slope.29 An extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to assist in the identification of prey.28 In deep water organisms, it may not be the centre of the eye that is enlarged. The hyperiid amphipod s are deep water animals that cater on organisms above them. Their eyes are almost divided into two, with the upper region thought to be involved in detecting the silhouettes of potential preyor predatorsagainst the faint light of the sky above. Accordingly, deeper water hyperiids, where the light against which the silhouettes must be compared is dimmer, have larger upper-eyes, and may lose the lower portion of their eyes altogether.28Depth perception can be enhanced by having eyes which are enlarged in one direction distorting the eye slightly allows the aloofness to the object to be estimated with a high degree of accuracy.9 Acuity is higher among male organisms that mate in mid-air, as they need to be able to spot and assess potential mates against a very large backdrop.28 On the other hand, the eyes of organisms which operate in low light levels, such as around dawn and dusk or in deep water, tend to be larger to increase the amount of light that can be captured.28 It is not o nly the shape of the eye that may be affected by lifestyle. Eyes can be the most visible parts of organisms, and this can act as a pressure on organisms to have more transparent eyes at the cost of function.28 Eyes may be mounted on stalks to provide better all-round vision, by lifting them above an organisms carapace this also allows them to track predators or prey without moving the head.9 editVisual acuityA hawks eyeVisual acuity, or resolving power, is the ability to distinguish fine detail and is the property of cones.30 It is often footstepd in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white/black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m surmount from the eye, it will subtend an angle of 1 degree, so the number of white/black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a gray block, is then the measurement of visual acuity of the eye.For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD31 (1.2 second per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD.32 A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eyes central fovea region. Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair.33 A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans. editPerception of coloursColour vision is the fa culty of the organism to distinguish lights of different spectral qualities.34 all told organisms are restricted to a small range of electromagnetic spectrum this varies from creature to creature, but is mainly between 400 and 700 nm.35 This is a rather small section of the electromagnetic spectrum, probably reflecting the submarine evolution of the organ water blocks out all but two small windows of the EM spectrum, and there has been no evolutionary pressure among land animals to broaden this range.36 The most sensitive pigment, rhodopsin, has a circular response at 500 nm.37 Small changes to the genes coding for this protein can tweak the peak response by a few nm2 pigments in the lens can also filter incoming light, changing the peak response.2 Many organisms are unable to discriminate between colours, seeing instead in shades of grey color vision necessitates a range of pigment cells which are primarily sensitive to smaller ranges of the spectrum.In primates, geckos, and othe r organisms, these take the form of cone cells, from which the more sensitive rod cells evolved.37 Even if organisms are physically capable of sharp different colours, this does not necessarily mean that they can perceive the different colours only with behavioural tests can this be deduced.2 Most organisms with colour vision are able to detect ultraviolet light. This high energy light can be damaging to receptor cells. With a few exceptions (snakes, placental mammals), most organisms avoid these effects by having absorbent oil droplets around their cone cells. The alternative, developed by organisms that had lost these oil droplets in the course of evolution, is to make the lens impervious to UV light this precludes the possibility of any UV light being detected, as it does not even reach the retina.37 editRods and conesThe retina contains two major types of light-sensitive photoreceptor cells used for vision the rods and the cones. Rods cannot distinguish colours, but are respon sible for low-light (scotopic) monochrome (black-and-white) vision they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are no(prenominal) at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina. retinal cones are responsible for colour vision.They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are mostly concentrated in and near the fovea. Only a few are present at the sides of the reti na. Objects are seen most sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are stimulated by light, the nerves send off impulses through these fibres to the brain.37 editPigmentationThe pigment molecules used in the eye are various, but can be used to define the evolutionary distance between different groups, and can also be an aid in determining which are closely related although problems of convergence do exist.37 Opsins are the pigments involved in photoreception. Other pigments, such as melanin, are used to shield the photoreceptor cells from light leaking in from the sides. The opsin protein group evolved long before the last common ancestor of animals, and has continued to diversify since.2 There are two types of opsin involved in vision c-opsins, which are associated with ciliary-type photoreceptor ce lls, and r-opsins, associated with rhabdomeric photoreceptor cells.38 The eyes of vertebrates usually contain cilliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, and that remnants survive in the eyes.38Likewise, c-opsins have been found to be expressed in the brain of some invertebrates. They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into the brain on metamorphosis to the adult form.38 C-opsins are also found in some derived bilaterian-invertebrate eyes, such as the pallial eyes of the bivalve molluscs however, the lateral eyes (which were presumably the ancestral type for this group, if eyes evolved once there) always use r-opsins.38 Cnidaria, which are an outgroup to the taxa mentioned above, express c-opsins but r-opsins are yet to be found in this group .38 Incidentally, the melanin produced in the cnidaria is produced in the same fashion as that in vertebrates, suggesting the common descent of this pigment.38