BIOL 3800 1st Edition Lecture 12 Outline of Current Lecture I. Test Errors A. 2 FreebeesII. Vision ReviewA. Anatomy of EyeB. Physical OpticsIII. Electromagnetic SpectrumA. Electromagnetic SpectrumIV. RetinaA. Structure of RetinaCurrent LectureVision Review Last Review Chapter 7I. Test ErrorsA. 2 Freebees 1. On the test question 74 is going to be a freebee because of wording so this adds 1 point to your test. 2. 39 is also a freebee and if you got b or e then you will have 1 point added to your test. But only a freebee if you got b or e.II. Vision ReviewA. Anatomy of Eye1. We looked at vision quickly before so this time we will go a little more in depth. Most of us have seen the eyeball or most of us know the terminology so most important thing is the tissue layers that make up the eyeball. 2. We don’t have to worry about the rectus tendon we don’t have to worry about too much about the canal of schlemm other than that it is for pressure equalization in eye3. You need to know where ciliary muscles are and that they are not very large and instead of pulling on the lens they do just the opposite. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. The ciliary muscles relax the tension in the zonula fibers and suspensory ligaments and allow the lens to round up on its own. The lens is elasticallyand always in a slightly stretched state. This mechanism is a little weird but important to understand otherwise you will not understand presbyopia. b. When your dad sits there with a paper far away and still can’t read it that well this means the lens cannot round up he can do all the contraction of ciliary muscles and pull the choroid layer forward and relax the tension in these fibers but the lens will not round up because its cross linked UV will cause this and so on. c. This is something that happens to all of us maybe we can prevent it in thefuture but right now we can’t. d. So consequently presbyopia which means that you cannot change the curvature would mean that you’re forming, if you’re reading something, the image behind the retina and normally at your age you allow it to become more spherical you would pull the image back onto the retina but if you’re past 45 and your image is cross linked it stays pretty much in the shape that it has. B. Physical Optics 1. Physical optics has some physics not that complicated just geometric way of finding out where object is formed. 2. The focal point is essentially determined by the curvature of the lens. 3. The lens does not have to be symmetrical. Let’s assume it is. So that means you have a focal point that is determined by this curvature if the curvature increases then you have a focal point that is closer to the center of the lens.4. These extremes are very important to figure out where you’re going wrong and in case you forget if you make the lens flatter and flatter until there is no curvature there is no focal point but the light goes right through anything flat does not have a curvature does not have a focal point. So as you flatten out the curvature the focal point goes further and further to the right until it doesn’t exist anymore.5. The mathematical formula 1/OD + 1/ID = 1/F will not give you the size of image but will give you the distance where image is formed from the lens.a. So with this formula you can figure out how to make a simple camera with it. Make sure you look at these ideas several times regarding thephysical optics portion and diagrams discussed in the previous lecture. So these things will sink in. b. That principle of refraction is used for these examples right here… again the only way you can understand it is to understand it is to realize it is an artificial construct in order to understand what is happening. There are many ways to draw this but he chose to draw all the lenses in the same plane for construction purposes and ofcourse we have a horizontal axis.c. By definition from this curvature of the lens and cornea we are ignoring itbut it’s there and also makes a contribution but we are only focusing on the lens by definition then we have an image plane and the image plane is the same for each of these eyeballs (image plane that doesn’t mean theretina is there that’s where the image is formed because that is a functionof the cornea and as we showed here of the lens) that is just for instructional purposes. 6. Nearsightednessa. So we know we have the same lens we have an image in the same plane, now suppose we have an oblong eyeball and the retina is behind the image plane then how do you pull or push the image onto retina how do you get it back? b. There is no way you would have to flatten the lens and you can’t do that you can’t pull on it so the only way you can do this is with corrective lenses or, and that’s why it’s called nearsightedness you come very close c. Then a new principle kicks in that are if the light rays come in at an angle the focal point is shifted. Under those circumstances when the image is sitting very close to the eyes then the image gets onto the retina but you don’t see much of it because it is so close. 7. Hypermetropia a. The other extreme is hypermetropia where you have a shortened eyeball or you have a misshapen cornea but we are going to look at the shortened eyeball it’s easier to explain the lenses are the same, the imageis now behind the retina and now the question is how can you pull it ontothe retina?b. You can pull the image onto the retina by constricting the ciliary muscles and allowing lens to round up now this is for distant objects so you are already straining by trying to pull the image onto the retina for distant objects so you will probably have headaches if it isn’t corrected because you constantly trying to contract your ciliary muscles in order to pull the image onto the retina because the contraction of the ciliary muscles loosens the suspensory ligaments of the zonula fibers and the lens if your lucky will round up elastically.c. So you can pull the image onto the retina now reading will still be a little difficult because that would make the situation worse if you come close to the eyeball you would tend to shift the focal point further back and your already constricting depending on the seriousness of the misshapeneyeball your already constricting the ciliary muscles to see something far away now