What I would like you to do is to find a topic from chapter 2 that you were interested in and search the internet for material on that topic. You might, for example, find people who are doing research on the topic, you might find web pages that discuss the topic, you might find youtube clips that demonstrate something related to the topic, etc. What you find and use is pretty much up to you at this point. But use at least 3 sources.
Once you have completed your search and explorations, I would like you to say what your topic is, how exactly it fits into the chapter, and why you are interested in it. Next, I would like you to take the information you found related to your topic, integrate/synthesize it, and then write about it. At the end, please include working URLs for the three websites.
By integrating/synthesizing I mean to take what your read/experienced from the internet search (and from chapter 1 if you like) organize the information into the main themes, issues, info, examples, etc. about your topic and then write about the topic in your own words using that information. This is hard for some people to do - many students write what we refer to as "serial abstracts." They are tempted to talk about the websites rather than the topic proper. They will talk all about website #1, start a new paragraph and talk all about web site #2, start a new paragraph and talk all about web site #3, and then write some kind of conclusion. Serial means one after the other...This what you DON'T want to do!
At first it is a real challenge to get out of the habit of writing "serial abstracts," but I assure you once you get the hang of it it is much easier to write using the integration method. And besides this is the way researchers and scientists write their technical reports and findings - many of you will have to be able to do this for other classes and for jobs that you may eventually be hired for so now is a good time to learn this skill. At this point don't worry about a grade, worry about doing your best to have fun with the topic and then integrate it into your own words to share what you found and now know. We will work on citing the sources later....
Let me know if you have any questions.
There was a very small section in Chapter 2 of the textbook which talked about how contact lenses worked. I wear contact lenses all the time, so I am very interested in seeing how this actually works and what types of problems with the eye can arise from this. One problem already stated in the book was that wearing them too long can irritate the cornea. The cornea then produces tears to protect the eye and regenerate the cornea. This actually happened to me just last night. I fell asleep with my contacts in and woke up at 8am with tears streaming from my eyes. Instead of complaining I was interested in this because I knew that I had just learned about this in my book! That is why I am so interested in this topic. It applies to me and my life, and maybe it will actually help me prevent some problems with contacts in the future!
There are a few different problems with the eye that will cause a person to need contact lenses or glasses. Emmetropia is when there is no problems with the refraction of the eye, and the refractions are matched perfectly to the length of the eye. This is when a person has 20/20 vision, and does not need corrective lenses. This is where accommodation comes in as well. This is when the eye changes its focus by changing the lens shape. This happens when the ciliary muscle contracts. As the book states, "the fatter the lens, the more power it has." Myopia, however, is when the light does not reach the retina. This is called nearsightedness. This light comes into focus in front of the retina, so distant objects cannot be seen as well. Hyperopia, however, is when the light comes into focus behind the retina. This is also called farsightedness. Astigmatisms are also a problem with eyesight. This is when the cornea is not spherical, and the vertical lines are focused in front of the retina and horizontal lines are focused behind it.
There are different ways in which these problems can be corrected with lenses. To correct a myopia, a negative (minus) lens would be used. These separate or scatter the light before it enters the eye. To correct a hyperopia, however, many young people can use accommodation. If that doesn't work, a positive (plus) lens is used to gather the light together before it enters the eye. To correct those types of problems, a spherical lens is needed. However, for an astigmatism, an aspherical lens is needed, because the cornea of an eye with astigmatism is not spherical. Lenses with two focal points are used to correct this problem.
There are also problems that arise from wearing contacts. Although contacts are safe to wear for the most part, if they aren't worn properly they can damage the eye. While the book states that wearing contacts for too long can be painful to the cornea, there are reasons for this. They can also cause other damage to the eye. Contacts can actually block a good amount of oxygen to the eye. This is why it is good to rest the eyes and take the contacts out at nights and whenever possible. Corneal ulceration or infection are some major problems that can arise from wearing contact lenses. Corneal ulcers occur when bacteria invades the cornea tissue causing infections that could even cause blindness. Eyes may become more sensitive as well. Pain and tearing are also signs of problems with the cornea which can normally be fixed with antibiotics within 24 hours.
All of these topics interested me and I'm glad I now know more about these issues with contacts. I will definitely be more careful about what I'm doing with my eyes. Sight is a wonderful thing!
Here are the websites I used to find this information.
http://www.healthscout.com/ency/68/346/main.html
http://www.shamirlens.com/patients/vision-conditions.aspx
http://www.emedicinehealth.com/contact_lenses/article_em.htm
I chose topic about Retinitis Pigmentosa disorder. In our book there is no much information about this topic, it just explains the main points of the disease and the author also gives the example of a person who had RP :"The man who could not see stars." I found couple interesting information about my topic that can tell more about treatment. I also found some new research and examples of people who suffer from RP. It is very uncommon condition affecting about 1 in 4000 people in United States.
Firstly, Retinitis Pigmentosa is an eye disorder that first causes progressively worse vision until not being able to see at all due to degeneration or dead cells in retina. Usually patients start having problem with night blindness then with central vision. Start losing rod cells that detect dim light and cones that detect light and color.
Some examples of patients with RP say that it is very difficult to recognize the symptoms of it, but what we all can prevent, especially knowing that someone else in our suffer from this disorder (since it is a genetic condition) they can wearing sunglasses to protect the retina from ultraviolet.
The treatment requires one medication or surgery; cataract extraction or transplantation of retinal patches. Dr. Marc J- Gannon talks about using telescope devises or microchip implants that go inside the retina is one of the treatment as well.
Some researches that have been done about Retinitis Pigmentosa at University of Pennsylvania took an important step with helping patients with RP. They make use of a viral vector in targeting rods in the retina safely and successfully.
In Australia, scientists have developed a bionic eye to improve the lives of patients with RP.
Prof. Yael Hanein of the School of Electrical Engineering
The prosthetic device they have made aims to replace the activity of the damaged photoreceptor cells. Columbia University Medical Center successfully utilized embryonic stem cells of mice to replace dead photoreceptor cells in a mouse with RP.
Sources:
http://www.youtube.com/watch?v=bCbV_kW1-Iw
https://health.google.com/health
/ref/Retinitis+pigmentosa
http://www.news-medical.net/?tag=
/Retinitis+Pigmentosa
http://www.brighthub.com/science/genetics/articles/73756.aspx
The topic I found interesting was that of dark and light adaptation which is talked about briefly in chapter 2. It is crazy to even think how fast our eyes react to dark and light situations. According to our book in bright illumination our pupils are 2mm whereas in the dark they quickly dilate to 8mm. There are four mechanisms underlying light and dark adaption which include pupil size, switchover from rods to cones, bleaching/regeneration of the photopigments, and feedback from the horizontal cells to control the responsiveness of the photoreceptors. Part of the mechanism is the switch-over from rods to cones. But even within the pure rod (or pure cone) regime there is still significant adaptation. Only a small part of the adaptation is due to changes in pupil size; the pupil diameter only ranges from 1 or 2 mm to about 8 mm, for an increase in area (or total light entering the eye) of a factor of 16-64. A lot of the adaptation occurs in the photoreceptors themselves. Part of the adaptation within the photoreceptors is due to photopigment bleaching - less photopigment available at high light levels results in weaker responses to light increments at those high light levels. Adaptation within the photoreceptors is also helped along by feedback from horizontal cells onto the photoreceptors to control the responsiveness of the photoreceptors. If the horizontal cells respond strongly then they tell the photoreceptors to turn it down a bit. When in a dark room it takes awhile for our eyes to adapt to the darkness but after about thirty minutes in the dark one is able to detect just a few photons. In addition, when one returns back to sunlight one can see almost instantly. Cones are less sensitive than rods (they function poorly in dim lighting) but there operating range is much larger. We use rods to see when the light is low and the cones take over when there is too much light for the rods to function well. After adapting to bright light, cones recover sensitivity quickly and then saturate. They are not very sensitive to very dim light. Rods recover more slowly but after thirty minutes or so they are very sensitive to dim light.
Furthermore, dark adaptation refers to how the eye recovers its sensitivity in the dark following exposure to bright lights. Dark adaptation forms the basis of the Duplicity Theory which states that above a certain luminance level (about 0.03 cd/m2), the cone mechanism is involved in mediating vision; photopic vision. Below this level, the rod mechanism comes into play providing scotopic (night) vision. There are four factors affecting dark adaptation, the first of these is intensity and duration of the pre-adapting light. This involves different intensities and duration of the pre-adapting light will affect dark adaptation curve in a number of areas. With increasing levels of pre-adapting luminances, the cone branch becomes longer while the rod branch becomes more delayed. Also, the shorter the duration of the pre-adapting light, the more rapid the decrease in dark adaptation. Second, size and position of the retinal are used in measuring dark adaptation. The retinal location used to register the test spot during dark adaptation will affect the dark adaptation curve due to the distribution of the rod and cones in the retinal which can be seen on a graph. Third, wavelength distribution of the light used, shows that when light of short wavelength is used, the rod-cone break is most prominent as the rods are much more sensitive than the cones to short wavelengths once the rods have dark adapted. Lastly, there is rhodopsin regeneration. Dark adaptation also depends upon photopigment bleaching. Retinal (or reflection) densitometry, which is a procedure based on measuring the light reflected from the fundus of the eye, can be used to determine the amount of photopigment bleached.
Moreover, with light adaptation the eye has to quickly adapt to the background illumination to be able to distinguish objects in this background. Light adaptation can be explored by determining increment thresholds. The bright light momentarily dazzles us and all we see is white light because the sensitivity of the receptors is set to dim light. Rods and cones are both stimulated and large amounts of the photopigment are broken down instantaneously, producing a flood of signals resulting in the glare. There are two ways in which adaptation occurs which are the sensitivity of the retina decreases dramatically and retinal neurons undergo rapid adaptation inhibiting rod function and favoring the cone system. Furthermore, the retina solves the problem by adapting to the ambient level of illumination.
http://webvision.med.utah.edu/light_dark.html
http://www.chm.bris.ac.uk/webprojects2003/white/light_and_dark_adaptation.htm
http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/light-adapt/light-adapt.html
http://www.youtube.com/watch?v=6lky4HqqDYE
I picked the topic of how our eyes adjust to darkness. There are four factors that effect how our eyes adjust to darkness, they are: intensity and duration of the pre-adapting light, size and position of the retinal, wavelength distribution of the light used, and Rhodopsin regeneration. Out of these factors I focused on wavelength and Rhodospin regeneration. The wavelength of the light used has a huge affect on how our eyes adapt to the darkness. When light is used that has a long wavelength, such as extreme red, our rods and cones work together to adapt to the light because rods and cones have similar sensitivities to light that has a long wavelength. This differs from when light with a short wavelength is used because rods are much more sensitive to light with short wavelengths. Another aspect that affects our eye adaptation is Rhodospin regeneration. Rhodospin regeneration refers to that fact that Rhodospin or visual pigment of rods, bleaches in light and regenerates in darkness. The amount of time that it takes the Rhodospin to regenerate has a direct affect on how long it takes our eyes to adjust to darkness.
Color spectrum with extreme red at the far right
http://en.wikipedia.org/wiki/File:Linear_visible_spectrum.svg
Sources
http://webvision.med.utah.edu/light_dark.html#wavelength
http://www.ncbi.nlm.nih.gov/pubmed/4056732
It is awesome that the cells are able to pump out compounds to replace the bleached ones so fast. I mean in a few minutes your vision is almost totally adjusted because the rhodospsin is regenerated. I remember reading a theory about sleep and why we sleep and it held that it is almost solely to rest the eyes. The eyes are so active all the time, firing about once per second and then increasing this rate when they are stimulated. So much exposure to light must tear on so sensitive of tissues they need those eight hours of protection.
When reading chapter 1 I became interested in cats hearing compared to humans. I have a cat and I always find it funny that as soon as I have my key in the door my cat is running down the stairs from my room. I found a couple of websites that discussed the high pitched frequency that cats are able to hear. The source said that cats can hear anywhere between 45 and 64,000Hz and humans can only hear between 64 and 23,000Hz. Everyone knows that cats have really good hearing, I have just never realized how much better it is compared to ours. I decided to go onto youbtube and find a test. I found it interesting because my cat would perk his ears up and look around for the noise and of course I couldn't hear a thing. When the pitch became to high for him he got annoyed and went upstairs.
Sources:
http://cats.about.com/od/healthfaqs/f/hearingsense.htm
http://animal.discovery.com/cat-guide/cat-anatomy/ears-hearing.html
http://www.youtube.com/watch?v=4G60hM1W_mk
For my topic I picked the disease Retinitis Pigmentosa. The book briefly discribes what the disease consists but I wanted to know more about the disease and if there were any current treatments available. I'm interested in this topic because i think that the mechanics behind the eye are really interesting and I dont know about diseases and problems that relate to loss of vision. Retinitis Pigmentosa(RP) is a disease where you lose night vision, have a loss of peripheral vision and have problems seeing in dimmly light areas. This disease is inherited through generations. 1.5 million people around the globe have been affected by RP. When I first started looking into RP there were sources saying there is no none cure for the disease. I tried to find current studies being conducted and how successful they were at restoring eyesight. I found that one clinic is have the patients go through acupuncture drinking Guangming decoction on a daily basis and taking antioxidants. These patients have shown great results saying that they have should be blind and instead their eyesight has improved. They have better night vision, and there eyes adjust. Some still have slight tunnel vision but still have shown improvements. I think that it is amazing that herbs and natural medicines can have an effect on a disease that eventually causes blindness. Another treatment that I found was taking 15,000 IU of a vitamin A supplement. Researchers have found that vitamin A has slowed down the process of RP. They also found that vitamin E should not be taken as a supplement if you suffer from RP because it actually progressed the rate of the diseases effects. I found these studies very intersting because of how far they have come with disease treatments. I found a link on youtube of patients who have been taking the first treatment and talking about how much they have improved and how it has affected there lives.
Sources
http://www.nei.nih.gov/news/pressreleases/rppressrelease.asp
http://www.youtube.com/watch?v=3VAUK7Su0Jk
http://www.tcmrp.com/index.html
The topic in Chapter 2 that I find most interesting is the degenerative disorder known as Retinitis Pigmentosa. The book goes into some detail by explaining that the disorder is caused by a progressive degeneration of photoreceptive cells and degeneration of the pigment epithelium. The disease effects rods first, which slowly eliminates peripheral vision, and then the cones die along, eventually leaving the effected person completely blind.
This disease is relatively rare and only occurs in 1 in 4,000 Americans, the most prevalent group is the Navajo Indians at 1 in 1878. Even with it's relative rarity, this disease is very inheritable since any RP carrying family member can put you at risk of developing it. Also, this disorder occurs in both men and women at the same rate. Having the RP gene also makes one more likely to develop hearing loss and another retinal disorder known as Usher Syndrom (a term used to describe a degeneration in both hearing and vision simultaneously).
This disorder progresses slowly, it's first noticeable as night blindness(Nyctalopia), and will then progress to loss in the visual field from the outside of the periphery inward. Patients also describe small flashes of light known as Photopsia.
Researchers find that the term Retinitis Pigmentosa is not actually the correct term to use. The suffix 'itis' of course means inflammation, but inflammation of the retina is not the inherent cause of cell loss. The true cause of the loss of photoreceptor is due to a hereditary degenerative effect in the protein structures of each cell. This makes proactive gene therapies the most viable solution to RP. The problem is that it is not one specific gene that causes this disorder. Researchers report that up to 45 different genes are responsible for causing problems, and the large amount of effected genes also explains why patients with RP usually have a few other disorders with it.
Treatments usually combine a two step approach. The first step is doctors will try to slow the degeneration with vitamins such as: Vitamin A, calcium channel blockers, Azetazolomide, and Lutein. The next level of treatment requires invasive surgeries to remove cataracts, transplantation of retinal material, and a gene therapy treatment that is still in the clinical trials phase. Doctors also hope to develop a prosthetic chip that can be implanted into they eye and act as a photo receptive retina. The vitamin treatments all seem to be limited beneficially, the surgeries seem to be a last ditch effort, and the implants are still being developed.
http://emedicine.medscape.com/article/1227488-overview
http://emedicine.medscape.com/article/1227488-treatment (the same root website, but completely different articles)
http://www.blindness.org/index.php?option=com_content&id=50&Itemid=67
http://www.lowvision.org/retinitis_pigmentosa.htm
The topic I was interested in after reading Ch. 2 is the problem of astigmatism. According to our book an astigmatism is a "visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea." An easier way to explain it is that the cornea is shaped like a football rather than a baseball. This will cause the light rays to focus on two points rather than one on the corenea, resulting in some blurred vision. I think most of us have seen the Acuvue commerical with the twin sisters and the line "Which one has the astigmatism?". If you have not seen it I included it in my sources below. So how do they correct for an astigmatism? In regular eyeglasses the lenses are made to have two focal points (or different focusing powers) instead of one to correct for astigmatism. Many people still believe that they can not wear contacts if they have an astigmatism. However, they have created contacts for astigmatism by making the contact have two curves on the surface and the bottom of the contact will be thicker to allow gravity to hold the two focus points in place (called prism balance). This works similar to regular eyeglass lenses to allow for correction of the astigmatism. Some people with astigmatism may also opt to get LASIK (Laser in-situ keratomileusis) refractive eye surgery. LASIK reshapes the cornea by removing tissue using an Excimer laser which is programmed based on calculations made from a topography of the corneal surface. "The laser then delivers the exact correction needed and send tiny spots of light beams to certain predetermined positions on your cornea in order to change the shape to what is required for you to see well." I thought this topic was interesting because even though our eyes may not always be ideal our technology will allow us to correct for it and our eyes will let us do it!
http://www.youtube.com/watch?v=5QXd1w3KWR0
http://www.ehow.com/video_4993065_astigmatism-contact-lenses.html
http://www.allaboutvision.com/conditions/astigmatism.htm
http://www.eyecaresource.com/procedures/lasik-laser-eye-surgery/
I chose to research the topic of “photic sneeze reflex”. I found it interesting because I sneeze when I go from dark to bright lights. I’ve also learned that when I feel a sneeze coming on, staring into a light will make it happen quicker. Why is this?
I found a couple different theories. Some theorize that because the optic nerve and the trigeminal nerve (which is responsible for sneezes) are so close together, when the optic nerve is stimulated by sunlight, the trigeminal nerve is stimulated too into thinking that the nose is irritated, which in turn causes a sneeze. Another theory suggests that people with this reflex have higher sensory responses. This theory was developed because of a study done that measured responses to light using an EEG. The experimenters found that people with this reflex had more brain activity in their somatosensory cortex as opposed to those without the reflex. A third theory relates to the information in the textbook - that wires in the brain are crossed. It says that the parasympathetic nervous system that feeds into the medulla oblongata is responsible for actions such as sneezing. The theory says that all the wires that control actions in our body are located in small areas and that it’s not unusual for some to be crossed.
I also discovered that this reflex is highly genetic. It’s an autosomal dominant trait so either the father or mother could carry it, giving their children a 50% chance to inherit the trait. Because this reflex isn’t dangerous, not much research has been put into the subject. However, looking deeper into the theory about the optic nerve/trigeminal nerve may bring light to different conditions such as epilepsy and migraines due to the fact that they can both be brought on by certain light conditions.
http://www.scientificamerican.com/article.cfm?id=looking-at-the-sun-can-trigger-a-sneeze
http://scienceblogs.com/neurotopia/2010/04/friday_weird_science_the_sunny.php
http://aebrain.blogspot.com/2009/04/photic-sneeze-reflex.html
In class we focused on just how amazing the anatomy of the eye is, and even though if someone today had the opportunity to design an eye they probably never or design it the way it currently is, it is nevertheless incredible functional. Our eyes and mind work together to create impressive vision.
First of all I think our photoreceptors, the rods and cones, are very interesting. The book explains the process of photoreceptors as capturing light and initiating the act of seeing by producing chemical signals. Rods help you see better in the dark, and motion, however little colors or details. Cones on the other hand capture different colors and fine details. “So we use rods to see when the light is low, and the cones take over when there is too much light for the rods to function well”. Rod takes longer to adjust, thus it takes longer for us to adjust to dark rooms then it is for us to adjust to light. This seems to be more of the few times we experience the limitations of our eyes. Another errors like our blindspot in the back of our eyes and our nose is naturally fixed by our brain.
I when to Las Vegas for last year, I went to see the Blue Man Group preform and I remember they did a segment about rods and cones. This video breaks down the functions in an understandable way. Also It explains the way that animation (or movie reels for that matter) work for our eyes. That there is a natural delay in the amount of light that your eyes can take in at once, and thus clips of animation work.
Another error in our eye, or at lease my eye that I am both “farsighted” or a condition called hyperopia and a slight astigmatism. From what I understand from the book emmetropia is when the light reflects on your perfectly on to your retina. This depends on the power of our “optical components” like the power of our lens. “Accommodation enables the power of the lens to vary by as much as 15 diopters”. Errors happen when the eyeball is too long or short for the power of the optical component. Myopia is nearsightedness and the eyeball is too long. On the other hand, hyperopia or farsightedness is whenthe eyeball is too short.
The book states that accommodation can correct Hyeropia in young people. My siblings have been wearing contracts since we were young. We all have very terrible myopia and have slight astigmatism. My sisters have progressed and become legally blind. Our parents both have bad eyes but nothing to the extent of us. I am wondering if that as we wear contacts all the time, our eyes become more accommodated and our eyesight gets worst. However according to the article “Do Contracts Make Your Eyes Worse?” this is not the case. The article is not the case, that it is common for many children to experience “myopic creep”. The article cites a study where haft the children wore contact lenses and the other half were assigned to wear eyeglasses during three-year study period, there is no difference.
I also wanted to look to how astigmatisms affected your visions, according to the article in WebMD, most of the focusing power occurs in the cornea. The article also states people with a small astigmatism are able to correct with blinking, which means sense. I remember that my Grandpa got glasses to correct his small astigmatism. He felt that things were falling off the table. As a result, my mom never wanted to try and fix any of our astigmatisms. “Astigmatism can run in families and often occurs in combination with other refractive problems such as nearsightedness and farsightedness”.
http://www.allaboutvision.com/contacts/faq/cls-eyes-worse.htm
http://www.webmd.com/eye-health/understanding-astigmatism-basics
http://www.youtube.com/watch?v=W-yLfm5HsHc
I found presbyopia to be particularly interesting because it is an inevitable symptom of old age.
When the author explained that this is something we all have to look forward to, I started wanting to
know more about treatment options as well as what causes this disorder. The textbook simply says that
the main reason presbyopia happens is because the lens hardens with age and the capsule around the
lens loses elasticity. The onset of presbyopia is typically around the age of 40 but symptoms do progress and most people will have this difficulty by age 60. Individuals usually begin to notice that they are developing symptoms of presbyopia when they are finding it difficult to read things because of blurred
vision when trying to focus on close things. However, it is necessary to get an eye exam to confirm a diagnosis. According to the Helmholtz theory of accommodation, the reason that these individuals find it difficult to read things that are up close can be attributed to their relaxed ciliary muscle. When individuals lose their ability to accommodate in this way flattens the lens and increases the focal length. Every individual with presbyopia is different and the varying degrees ofseverity require different types of treatment. Treatment can range from bifocal lenses (most common),to multifocal contacts, and even surgery. Conductive keratoplasty is an example of a surgery used to help make the lens more curved in order to decrease the focal length and help individuals see closer object more clearly. After reading a little about treatment options for presbyopia, I noticed that there are also a lot more trial surgeries and treatment options that will (hopefully) be available in the future
(if effective). Hopefully sometime in the future the authors will be wrong and this condition will be
avoidable. If anyone is interested in presbyopia or just wants to check out what an optometrist with too
much time on her hands looks like there is also a video at bottom.
1. http://www.youtube.com/watch?v=rxZ8IjdpzDg&feature=related
2. http://www.sciencedirect.com.proxy.lib.uni.edu/science?_ob=MImg&_imagekey=B6T0W-3WTP16P-2N-1&_cdi=4873&_user=724663&_pii=S0042698997001028&_origin=search&_coverDate=01/31/1998&_sk=999619997&view=c&wchp=dGLbVlW-zSkzk&md5=0006f1c451a8beab9f64bd8bfeea88bf&ie=/sdarticle.pdf
3. http://www.allaboutvision.com/conditions/presbyopia.htm
4. http://www.mayoclinic.com/health/presbyopia/DS00589
I am researching color blindness. I have a sort of amateur understanding of the condition, but I would like to find out more details on causes and the mechanisms involved.
Color blindness occurs when there are a lack of cones of a certain light sensitivity. There are several types and males have been shown to suffer a higher rate of color blindness than females. Monochromacy is referred to as true color blindness because there is no distinction between any color of light striking the eye. Sometimes this condition arises because there are literally no cones present, rod monochromacy, and sometimes cones are present but are defective or only cones sensitive to a single frequency are present, cone monochromacy, so they can see only one particular color. Dichromacy refers to when one of the three types of cones is not present and color vision is reduced to two dimensions.(that was a pretty close paraphrase maybe a little too close but wikipedia worded it so well) A very common form of color blindness is red-green affecting something like 8 to 10 percent of males. This is a dichromatic condition.
Nearly every site I looked into that had information about color blindness held that there was no treatment for inherited color blindness, but an article in Time magazine featured a physiotherapist who claimed to have made significant strides in treating color blindness. Brooklyn Doctor Henry Cadan had started a regimen that has appeared to have showed improvement in 25% of the subjects. His standards for measuring "improvement" were the military's entrance requirement. That is to say most military branches don't allow colorblind individuals to join but with his regime about 25% of Cadan's participant's were able to pass military screening. His method included injecting large amounts of Vitamin A and Vitamin B, electrical stimulation to the muscles in the eye (i'm assuming the ciliary muscles although the article fails to specify) and training with special red and green glasses and red and green spectrum lights. While reading this article I didn't know what to make of it. Then I saw the article is from 1943! It mentions how most of the subjects are about to be drafted anyway so they were trying to volunteer. This regimen seems to good to be true, and most sources that are more recent than World War 2 agree. (although just a simple search gave me some links for gene therapy studies and such and a wiki page) Not knowing the article was from the 40s and finding that out at the end is a mind trip. I thought the procedures sounded a little primitive and possibly unethical but the date made it snap all into place. So unfortunately I don't put much value into this articles scientific worth. I have trouble believing the news reports that are going on today, I really don't even know how to analyze a time Magazine article from the 40s.
An abstract for a journal article in some optometry magazine (GEORGE WALD, "Blue-Blindness in the Normal Fovea," J. Opt. Soc. Am. 57, 1289-1301 (1967)
http://www.opticsinfobase.org/abstract.cfm?URI=josa-57-11-1289) suggests that every person has an area in the center of the fovea that is blue-blind, that is it lacks the cones needed to transmit the information of blue spectrum light. If this is a normal condition of the eye, as the study seems to suggest, then perhaps cones are color coded as far as their distribution on the surface of the retina. The study suggests that this area in the center of the fovea is more abundant in red-green sensitive cones and that these get fewer in frequency toward the edge of the fovea. Why do blue sensitive cones seem to distribute only on the outside of the fovea? Well I know blue is a higher energy color than both red and green so maybe it has something to do with the angle of the light striking the cell and if that angle has an effect on the way blue light can be sensed by cones. It seems science is coming closer to a sort of map of the retina. If such information could be compiled and we were able to see the normal structure of the retina down the the distribution of which color sensitive cones are where we may be able to apply the knowledge toward therapy or treatment for the color blind.
http://en.wikipedia.org/wiki/Monochromacy
http://www.uic.edu/com/eye/LearningAboutVision/EyeFacts/ColorBlindness.shtml
http://www.time.com/time/magazine/article/0,9171,802584,00.html
http://www.opticsinfobase.org/abstract.cfm?id=75312
http://en.wikipedia.org/wiki/Gene_therapy_for_color_blindness
The topic I chose to learn more about from chapter two was mach bands. Mach bands are illusory stripes that can be seen when two areas of different contrast are next to each other. The cool thing about mach bands is that putting to regions of different contrast together don't physically make an illusory stripe, the stripe is formed by our visual system. Seeing a mach band is seeing something that isn't physically in front of you. This visual phenomenon is caused by lateral inhibition. Lateral inhibition of the photoceptors is caused by the photocepotrs center of receptive field falling in between two areas of different contrast. Depending on how much of the receptive field is in between two different contrasts the lateral inhibition causes that receptor to either see the entire section as lighter or darker. When one receptor sees an entire section as darker or lighter, it makes our brain see a stripe in between the two sections.
I think this phenomenon is important in understanding the visual system because it is a very clear example of the brain "seeing" more than our eyes do. We know that our brain fills in a lot of the gaps in our vision, mach bands are a good example of this.
http://www.nku.edu/~issues/illusions/MachBands.htm
http://www.siggraph.org/education/materials/HyperVis/vision/latinib.htm
http://www.google.com/images?um=1&hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&biw=1440&bih=710&tbs=isch%3A1&sa=1&q=mach+bands&aq=f&aqi=g4&aql=&oq=
I like your discussion of mach bands (illusory stripes) and how it relates to lateral inhibition (where one cluster of receptive fields wants to inhibit the other-antagonism). I think it is interesting that our visual system exaggerates the change from light to dark. I think the graph that was shown in class helped me understand how the center surround cells create this illusion. A bright Mach band is a result of a center surround where its center was just within the bright panel but part of its surround is in the darker panel. There is less antagonism & it creates a stripe.
I had a hard time understanding lateral inhibition at first, so it was nice to be able to read your description of it as well as the Mach Bands. What interested me about lateral inhibition is that there is competition with the receptive field. One side of the field is trying to inhibit the other when there is a difference in contrast, which is what causes certain sections to be lighter or darker. It was a bit confusing to me because of the center surround cells, which include the ON-center cells (when the positive charges are in the center) and the OFF center cells (with negative charges in the center). When the center of the photoreceptors field lands in between two of the lines, that is what causes the bars to look lighter in the middle of the two.
I have been having a hard time understanding exactly how lateral inhibition works as well. Reading your description really helped me get a better understanding of it. I knew that lateral inhibition had something to do with center surround cells and one side trying to inhibit the other side. Other than that I was having a hard time piecing it together. The way you explained lateral inhibition as occurring when the center on the cell is receiving a dark signal on one side and a light signal on the other. Depending on which signal is stronger, it will determine weather our visual system perceives it as dark or light, and this is was creates the illusion of mach bands.
The topic from chapter 2 that i decided to learn more about was astigmatism. I decided to look more into this topic because I have an astigmatism in both eyes and have had this ever since I was in second grade. The doctors always explained it to me that my eye was shaped like a football instead of a baseball. I always thought this meant that my eyes were shaped differently than everyone elses. However, now that I am older and have done some research on it, I know that it is not my whole eye but is the cornea. The text briefly mentions myopia, hyperopia and astigmatism so I decided to do some more research on astigmatism and see what else I could learn about it.
According to our text and all three websites, an astigmatism occurs then the cornea is oblong (shaped like a football) instead of being spherical (shaped like a baseball). When the cornea is oblong it makes it impossible for the light to focus at one single spot. Making people with an astigmatism have blurry vision.
The cause of an astigmatism is not really known. Some people may be born with an astigmatism, while others will develop it over time. Some other possible causes are eye injury, certain types of eye surgery, the weight of the upper eyelid on the eyeball, and scarring of the cornea. Astigmatisms are also hereditary. Another possible cause of astigmatisms is keratoconus, in which the cornea progressively becomes cone-shaped and thin. This is a very rare case, and is more common in women than in men.
There is also another form of astigmatism, which is called lenticular astigmatism. The causes of this astigmatism are a little different than the causes of a corneal astigmatism. Lenticular astigmatism is caused by abnormalities the crystalline lens that also focuses incoming rays instead of an oblong shape of the cornea. Metabolic diseases are the primary cause of this type of astigmatism. An example that WebMD provides is that of high blood sugar. Being a diabetic with high blood sugar could change the shape of the crystalline lens which would distort vision and lead the person to have an lenticular astigmatism. However, once the blood sugar levels are controlled by taking medicine/insulin, the original shape of the crystalline lens would be restored and the astigmatism would diminish.
An astigmatism can be treated by wearing corrective glasses or contacts.
http://www.webmd.com/eye-health/understanding-astigmatism-basics
http://www.youtube.com/watch?v=imqHSIhXxn4&feature=related
http://www.allaboutvision.com/conditions/astigmatism.htm
I chose to look into the photic sneeze reflex. I find this topic interesting because I’m one of the 10-35% of the population that is affected by it. The text states that there is currently no known reason for this to occur. This reflex has always been a mystery, however, there are 2 main hypothesis as to why it happens.
A sneeze is triggered by an irritation to our noses. When this is happened it is sensed by the trigeminal nerve. When our eyes take in a sudden burst of light our optic nerve sends a signal to the brain to constrict our pupils. The two nerves are very close together and some scientists believe that when the optic nerve fires the signal it is sensed by the trigeminal nerve and then mistaken as an irritant to the nose causing us to sneeze.
The other theory is based on the idea that the medulla oblongata basically confuses our reflex actions. The theory suggests that when we get a strong intake of light our pupils contract involuntarily which is a parasymphatic response. Along with other parasymphatic responses the nerve responses to the medulla oblongata which is where the sneeze centre is located. The theory suggests that the medulla is a “tangled web of cross-talking nerve wires” and that sometimes it doesn’t respond appropriately. This theory isn’t based only on the photic sneeze reflex. Apparently, some people have other sneeze reflexes that our related to parasymphatic responses such as when we become full our gastric juices flow and during sex blood flows to the genital area.
Both theories seem to agree that the reflex is genetic. It’s an autosomal dominant trait which means if one of your parents sneeze in the sun you have a 50% chance of also sneezing. Because of this a group in the ‘70’s created a new name, Autosomal-dominant Compelling Helio-Ophthalmic Outburst syndrome . (ACHOO) .
Scientists are starting to do more in depth studies of this reflex. It seems rather harmless however some military personnel felt it could be dangerous for fighter pilots but they’ve found that sunglasses will get rid of it. Other scientists believe it could shed light on other medical issues such as epilepsy and migraines because of their related neurology.
Unfortunately, there currently isn’t really evidence to support any of the theories out there. However, studies seem to be popping up around America studying this phenomena but until then it will remain a joke to many people.
http://www.scientificamerican.com/article.cfm?id=looking-at-the-sun-can-trigger-a-sneeze
http://aebrain.blogspot.com/2009/04/photic-sneeze-reflex.html
http://www.scienceline.org/2009/11/why-do-some-people-sneeze-when-they-look-at-the-sun/
The topic that I decided to do more research on from chapter 2 is Retinitis Pigmentosa (RP). The reason this topic interest me is because it is something that I seriously thing I might have in the future. The reason I say this because my eyes are bad, and always have been more even more, I notice difficulty seeing while driving at night. I watched a youtube video from Dr. Gannon. While watching it, the problem with having difficulty while driving at night started to make sense. According to Dr. Gannon, if you do have RP, your rods begin to die. Our Rods are responsible for seeing at night. This could be one possible reason while it is a bit difficult for me to drive at night. This is nothing severe, but it can be in the future. Dr. Gannon says that this is a hereditary genetic condition… my mom hates driving at night! A sign or RP? I think so. This all takes place in the retina. According to Dr. Gannon, it starts in the periphery. RP also cause people who suffer from it to lose peripheral. This is something that I am very afraid of because it affects your mobility. I can’t even imagine what it would be like walking and only being able to see straight ahead of you. Even scarier is that Gannon says that we don’t have a “definitive tunnel” in our center vision. To me this means that things might be in a blur around what is straight ahead of us, I cannot imagine seeing a blur every day.
Dr. Gannon talks about two ways that are used to treat RP. The first was is field expansion lenses. The second way is am orphic lenses. While both of these treatments do help, neither of them solve the problem entirely. As I said earlier RP affects your mobility, but also your depth perception and glare sensitivity. This is a topic I am really glad I did further research on because it is something that really does worry me. Now that I can explain it, I am going to call my mom and see if she has any other signs other than having difficulty driving at night.
http://www.youtube.com/watch?v=bCbV_kW1-Iw&feature=related
In chapter 2 we learn a lot about the different types of eye conditions and how they can or cannot be corrected. One of the eye conditions that caught my attention was cataracts. Cataracts are opacities of the lens and they are caused by irregularity of the crystallins. Crystallins are a class of proteins that make up the lens. The lens is normally transparent because of the crystallins. Anything that interferes with the regularity of the crystallins will result in loss of transparency. Check out these two videos and see how your view on cataracts and life changes.
http://www.youtube.com/watch?v=nWGELAmOjKc&feature=related
http://www.youtube.com/watch?v=lPIX3ca9LPc