Anna Leng 2b-3 (annaissbananas@gmail.com)
Sunday, March 27, 2011
Eye see you
In chapter nine, Shubin talks about how our eyes allow us to see things. Explain what happens to the eyes on the molecular level when someone becomes near-sighted or far-sighted. Do animals' eyes also experience near or far-sightedness? If so, how do they adapt to this evolutionary disadvantage?
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When someone is near-sighted or has myopia, this means that they are able to see things close to them very clearly. This happens because the eye ball is longer than usual. The path of an image starts at the pupil, a small black opening in the center of the eye. Light travels through the pupil and the amount of light depends on the iris, the colorful area surrounding the pupil. This muscle opens and closes the pupil according to the environment a person is in. A person in a dark room has dilated pupils because the pupil needs a lot of light that is not readily available. For a person a in a bright room their pupils will constrict because there is so much more light than the pupil needs so it makes sure that only certain amount gets into the eye. After the light passes through the pupil, it reflects the image seen by that eye onto the lens. The lens then reflects the image up-side down on the retina which is the back layer of the eye. The up-side down image is then processed right-side up by the brain and the image is sent through the optic nerve to the Occipital lobe through the thalamus (Bedinghaus). Since the eye ball is longer than what it should be, the image from the lens is not focused on the retina. It is focused in front of it therefore making the person unable to clearly see far away objects.
ReplyDeleteFor a person to far-sighted means that they will not be able to see things that are close to them very clearly. The only difference is that their eyeballs are shorter in length than normal so the lens will focus the image behind the retina rather than on it.
When it comes to animals, they can also have nearsightedness or farsightedness because are as likely to have eye developmental defects as humans do. In a study done of animal eyesight, “animals raised in small cages tend to be nearsighted” (“Do animals have”). Animals in cages are not in their natural environment so they are not exposed to their regular viewing habits, thus, affecting their eye development. “Most wild animals seems to have perfect vision”, because they are exposed to their environment and they develop their viewing habits naturally (“Do animals have”).
Animals do not have a hard time adapting to their poor eyesight because it depends on the environment they live in and the things they expose their eyes to. If animals spend a part of their life in cages and then they spend their life out in the woods, their eyes will slowly adjust to the different things they are seeing. This concept also applies to humans. There is evidence that “intense close-up activities, such as reading for prolonged periods of time at close range or playing video games for many hours, in early adulthood can induce nearsightedness” because the eyes are so used to focusing on close up things, that it seems like they “forget” how to focus far away objects after a while (Bedinghaus). In order for any living thing to have perfect vision, one the important things to do is to make sure to expose eyes to both close and far away things for about he same period of time.
Chandrika D
(shiningstar0393@gmail.com)
Bendinghaus, T. “The Basics of Nearsightedness”. Retrieved on March 28, 2011, from
http://vision.about.com/od/commonvisionproblems/a/nearsighted.htm
“Do animals have eye problems and need glasses the way humans do?” Retrieved March
28, 2011, from
http://yucky.discovery.com/flash/askwendell/answers/990329glasses.html
As Chandrika mentioned above, near-sightedness is the inability to see things that are far away and only being able to see things that are near by. This happens because light entering the eye is not focused correctly, therefore distant objects appear to be blurred. People have the ability to see things because the front part of the eye refracts light and points and points it back to the retina (which is the surface of the eye). Nearsightedness occurs because the optical length and physical length of the eye is not the same - the physical length is greater than the optical. When this happens, it is more difficult to focus the light directly on the retina and therefore the images are blurry.
ReplyDeleteFarsightedness is when one cannot see things that are nearby, but can see things that are farther away very well. This happens because the image is focused behind the retina instead of directly on it. This may happen because the eye is too short or the cornea is too flat.
Nearsightedness and farsightedness is, in fact, possible in dogs and other animals. This is because the eye in an animal such as a dog or a cat function in similar ways as the eyes of human. This means that there can be issues with the refraction of light that humans face which cause things like near and farsightedness. In general, most dogs and other animals have slight myopia, but there are cases of hyperopia and there have been reports of astigmatic dogs as well. This means that some dogs cannot completely focus on one thing, therefore their vision is always a little bit blurred. There are special cases, such as guide dogs, that have a lower prevalence of myopia due to their need for rigorous optical and visual performance. These dogs have had to adapt to their environment, and being necessary for guiding blind people, they need to have more keen and sensitive eyes, therefore overcoming things such as near or farsightedness. In general, any animal that has eyes is susceptible to experiencing some kind of disadvantage in vision, whether it is near or farsightedness or an astigmatism.
Sujin Ko (sujinko93@gmail.com)
Sources: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002018/
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002015/
http://www.iovs.org/content/33/8/2459.full.pdf
http://en.wikipedia.org/wiki/Astigmatism_(eye)
As stated by Sujin and Chandrika, near-sightedness, or myopia, is the inability of the eye to perceive objects or sights that are distanced from the eyeball. A person may become near sighted if the eyeball is too long, or if the cornea has too much curvature. What occurs with myopia, as stated by Sujin, is more based on the physics of light entering the eye. Due to the physical mutation of the eye, light that enters cannot be properly focused on the retina, which makes far images appear blurry. This relates to the biological theme of relationship between structure and function. In the normal eye, the physical length does not exceed the optical length, so the eye is able to properly refract light onto the retina. However, when the eye's structure is altered either by physical stress(such as watching a digital screen for a long period of time close to the eyes, or focusing very intensely on a book close to the face) or by heredity, since the structure is directly related to the function, the eye is no longer able to do its job, and the blurry vision negatively impacts the person, because they are unable to do many daily processes.
ReplyDeleteAccording to www.ncbi.nlm.nih.gov, "Farsightedness is the result of the visual image being focused behind the retina rather than directly on it. It may be caused by the eyeball being too small or the focusing power being too weak. Farsightedness is often present from birth, but children have a very flexible eye lens, which helps make up for the problem. Most children outgrow the condition." This also relates to the theme of structure and function, just as how the altered eye in near sightedness leads to an impact on its ability to function, this condition results in the same problem.
As Sujin stated, dogs and cats can often have near or far sighted vision, just as humans do. This is because of the idea that there can be mutations of genes that correspond to the length and power of the eye in cells, which can lead to a defect of the eye, and thus, the inability for the organ to function. In addition, many apes can also have astigmatism, which can provide difficulty for them in finding food or traveling throughout their daily life. Just as in humans, these conditions can be inherited, or caused from physical stress. Although dogs, cats, and apes cannot wear contact lenses or eyeglasses, they can often make up for it by having enhanced senses. For example, Great White sharks have horrible eyesight, and can barely see things that move in front of their eyeballs. However, similarly to dogs, these sharks have adapted very strong senses of smell, by developing genes that code for higher numbers of olfactory receptors in their nasal passages, resulting in a better sense of smell. Since this sense is much more sensitive, sharks are able to track down prey and also other objects that remain in their paths, to help compensate for their lack of eyesight. Thus, these conditions have caused adaptations in the wild, that help to adjust to inherited disadvantages.
Sources:
http://www.aoa.org/myopia.xml
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002018/
Campbell
Matt Kim
(matthewkim0803@gmail.com)