From aeulenbe@indiana.edu Ukn Feb 7 09:55:41 1995 Date: Tue, 7 Feb 1995 09:20:19 -0400 (EST) From: Alex Eulenberg Subject: Re: Astigmatism Status: RO X-Status: Marco asks: > Does anyone know the medical explanation/definition of astigmatism? According to my Mirriam-Webster's 9th, astigmatism is when "rays from a point fail to meet in a focal point resulting in a blurred and imperfect image." This would make it sound like near- and farsightedness are just special cases of astigmatism. As the word is most commonly understood, though, astigmatism is the condition where the lens or the cornea (more often the cornea) is warped so that depending on what the angle is, a line will be more or less out of focus. So, for example, a vertical line could be clear, while one at a 15 degree angle could be fuzzy. Can astigmatism be cured using home therapy? I think so. At least part of what causes astigmatism is the same thing that causes nearsightedness -- strained muscles pulling improperly on the lens or on eyeball as a whole (which may particularly affect the cornea). Also, if you improve your ability to accommodate (adjust for distance) -- the astigmatism will diminish somewhat. I quote from the sci.med.vision FAQ: :Astigmatism causes images to be out of focus no matter what the distance. :It is possible for an astigmatic eye to minimise the blur by accommodating, :or focusing to bring the "circle of least confusion" onto the retina. --Alex Eulenberg ========================================================================= From r.malingre@qut.edu.au Ukn Feb 8 09:50:29 1995 Date: Wed, 08 Feb 1995 15:54:48 +1000 From: r.malingre@qut.edu.au (Rene Malingre) Subject: Re: Astigmatism Status: RO X-Status: >Marco asks: > >> Does anyone know the medical explanation/definition of astigmatism? > >According to my Mirriam-Webster's 9th, astigmatism is when "rays from a >point fail to meet in a focal point resulting in a blurred and imperfect >image." This would make it sound like near- and farsightedness are just >special cases of astigmatism. > >As the word is most commonly understood, though, astigmatism is the >condition where the lens or the cornea (more often the cornea) is warped >so that depending on what the angle is, a line will be more or less out of >focus. So, for example, a vertical line could be clear, while one at a 15 >degree angle could be fuzzy. > >Can astigmatism be cured using home therapy? I think so. At least part of >what causes astigmatism is the same thing that causes nearsightedness -- >strained muscles pulling improperly on the lens or on eyeball as a whole >(which may particularly affect the cornea). Also, if you improve your >ability to accommodate (adjust for distance) -- the astigmatism will >diminish somewhat. I quote from the sci.med.vision FAQ: This is not true... Looks like you will have to look further in to what astigmatism is. If you are a hyperopic astigmat, both line foci fall behind your retina. The circle of least confusion, of course, lies between these two line foci. If a hyperopic astigmat (or a mixed astigmat) accomm- odates to bring the circle of least confusion on to the retina, his vision will be best overall. However, if horizontal lines were previously clear, they would now be blurry; vertical lines would also be blurry, but equally with the horizontal lines, not blurrier as when the horizontal focus was on the retina. The dioptric distance between the two line foci will remain the same (in the vast majority of cases - I am an exception, which I will get to shortly), no matter where the circle of least confusion is. The measure of astigmatism is defined as the dioptral difference between the two line foci. Accommodation will not reduce the astigmatism, it will just minimize the blur, and only if you are a hyperopic astigmat, or a lucky mixed astigmat. Accommodation in a myopic astigmat, will of course increase the blur, just like accommodation in a myope will increase distance blur. Now, why am I an exception? When my right eye accommodates 8 dioptres, I gain 0.50 D of astigmatism. This is meridional lenticular astigmatism, caused by uneven contraction of the ciliary muscle, or uneven tension on the lens capsule by the zonule of Zinn. My left eye does't change. > >:Astigmatism causes images to be out of focus no matter what the distance. >:It is possible for an astigmatic eye to minimise the blur by accommodating, >:or focusing to bring the "circle of least confusion" onto the retina. > > >--Alex Eulenberg > > > > > > ''' (0 0) +----oOO----(_)-----------+ | Rene Malingre | | R.Malingre@qut.edu.au | +------------------oOO----+ |__|__| || || ooO Ooo ========================================================================= From ddawson@magnus.acs.ohio-state.edu Ukn Feb 9 09:07:45 1995 From: David J Dawson Subject: Re: Astigmatism Date: Wed, 8 Feb 1995 19:11:19 -0500 (EST) Status: RO X-Status: (again i apologize for my computer difficuloties, your letter of regard follows my reply) in regards to reducing astigmatic blur with respect to accommodating, the answer is not necessarily so, in fact it is OFTEN not so... the img progression that i described can be thought of as a fixed piece, the extremes being the two line foci with a circle (the COLC) at the dioptric midpoint (not the linear midpoint) between the two line foci... ina perfect system, the point object produces a point img. that falls on the retina...if you are nearsighted (with no astig) the point img is formed too quickly and falls in front of the retina...further addition of power by the lens only serves to focus light EVEN SOONER and hence place the img even MORE in front of the retina...with farsightedness (no astig) the eye does not have enough converging power, and the point img is formed after the light has reached the retina, forming a point img behind the retina...in this case, power can be added by the lens (accommodation) in order to place the focal point ON the retina assuming you have enough accommodative ability... having said that, with astigmatism, that focal "unit" can ALSO fall at any of these three scenarios...COMPLETELY in front of the retina (if the patient is myopic in all meridians, ie: both numbers on your astig.prescription are negative--for an optometrist's presciption), OR the unit may fall completely behind the retina for a hyperope in all meridians (both numbers of the prescription positive) OR the "unit" --which is called the interval of sturm, by the way--can straddle the retina...note that in this condition, the COLC can fall infront of, behind, or ON the retina... accommodation can only place the COLC on the retina WHEN IT IS BEHIND THE RETINA AND THERE IS ENOUGH ACCOMMODATIVE ABILITY TO FOCUS IT ON THE RETINA...therefore, myopes--and that is most of your target audience, i would think, CANNOT reduce astigmatic blur by accommodating! ...which was my point about your characterization being a bit oversimplified... as for the corneal change with accommodation...as i am unfamiliar with the specific article in question, i can only make educated guesses, BUT here goes...accommodtion, presumably is not designed to slter power by it's effects on the cornea, anychanges are like on a micrometer type scale...likely the effect is NOT significant with respect to changing the power of the eye...BUT if it DID in fact change the power sugnificantly, i would wager that b/c the accommodative muscles are in the form of annulus, the changes would be even across the cornea making a spherical change in the lens...spherical changes DO NOT alter the astigmatic need for correction...if you change the greatest power meridian and the lesser power meridian by the same value, the net difference between the two is still identical, and the difference in powers between the meridians is what is DEFINED as astigmatism... i don't mean to rant and rave, so i apologize if this seems a bit confrontational...i just want to make sure that misconceptions are corrected and not disseminated...thanks for your response... dave. > That's all I think I said. > > Plus, I heard that the cornea acutally does change shape as a function of > pressure from the extraocular muslces (discovery by Roscoe of Accomotrac > fame). > > --Alex > ========================================================================= From BABO@ix.netcom.com Ukn Feb 9 09:07:48 1995 Date: Wed, 8 Feb 1995 18:09:34 -0800 From: BABO@ix.netcom.com (Paul Harris) Subject: Re: Astigmatism Status: RO X-Status: Marco, You wrote: > >Good Morrow fellow people... >Does anyone know the medical explanation/definition of astigmatism? > Yes.... In fact I have published a paper on the topic. What would you like to know. It's actually a _VERY_ complicated subject which far too often is trivialized as an irregular shaped cornea or misaligned optics. Small amounts of astigmatism are secondary symptoms of visual stress. When the minus cylinder axis is at 90 degrees the primary problem is an accommodative disorder. When the minus cylinder axis is at 180 degree the primary problem is an eye teaming problem. This would be for amounts less than 1 diopter. For greater amounts the astigmatism relates to posture. The basic concept is that sustained assymetries will cause asymmetric development in the visual system. Our dictum in behavioral optometry is: Function alters structure. Hope this helps. Paul Harris, O.D., F.C.O.V.D., F.A.C.B.O. ========================================================================= From vicc@extro.ucc.su.OZ.AU Ukn Feb 9 09:19:55 1995 From: Vic Cinc Subject: Re: Astigmatism (fwd) Date: Thu, 9 Feb 1995 13:24:41 +1100 (EST) Status: RO X-Status: hi, >>Good Morrow fellow people... >>Does anyone know the medical explanation/definition of astigmatism? >> >Yes.... In fact I have published a paper on the topic. What would you >like to know. It's actually a _VERY_ complicated subject which far too >often is trivialized as an irregular shaped cornea or misaligned optics. > >Small amounts of astigmatism are secondary symptoms of visual stress. >When the minus cylinder axis is at 90 degrees the primary problem is an >accommodative disorder. When the minus cylinder axis is at 180 degree >the primary problem is an eye teaming problem. This would be for >amounts less than 1 diopter. what is teaming? I am slowly compiling a glossary of big opto words, and plan to buy some books when I get paid again. >For greater amounts the astigmatism relates to posture. The basic >concept is that sustained assymetries will cause asymmetric development >in the visual system. This makes sense. I have astigmatism of, from memory -0.75x178 -1.0x175, and I find posture plays a role in my double images. Vic ========================================================================= From ddawson@magnus.acs.ohio-state.edu Ukn Feb 9 09:48:42 1995 From: David J Dawson Subject: Re: Astigmatism Date: Wed, 8 Feb 1995 14:52:43 -0500 (EST) Status: RO X-Status: alex, [sorry i have not enclosed the appropriate clippings, but my computer is having difficulties] you have made some erroneous assumptions with regards to whether or not astigmatism lends itself to correction via vision therapy... it is true that in some cases of astigmatism you can accommodate to put the COLC (circle of least confusion) on the retina (but not in all cases of astigmatism)...HOWEVER astigmatism is an error due to shape of structures in the eye, usually the cornea) accommodation does not change the shape of the cornea at all... astigmatism as you have pointed out was oversimplified in the webster's dictionary (nearsightedness and farsightedness ar not specialized forms of astigmatism, though they can be related) but furthermore, your characterization of astigmatism is an oversimplification of the true concept...corneal shape remains constant at all distances, which is why astigmatism persists at all distances...however, a point object will be focused as a progression from a line, through a series of ellipsoids, to a blur circle (COLC), through more ellipsoids, and finally to a straight line oriented 90 degrees to the first...THIS IS THE IMG FOR EVERY SINGLE POINT IN AN EXTENDED OBJECT! depending on the state of accommodation AND the refractive error present in the eye, someone MAY be able to focus the COLC on the retina, such that every object poit forms a blur circle on the retina...this is the clearest possible focus WITHOUT changing the cornea shape, or using corrective lenses...(if this made no sense whatsoever, i would be willing to discuss it further as time permits)...i hope this has been of interest david. ========================================================================= From r.malingre@qut.edu.au Ukn Feb 9 18:24:08 1995 Date: Fri, 10 Feb 1995 08:36:18 +1000 From: r.malingre@qut.edu.au (Rene Malingre) Subject: Re: Astigmatism Status: RO X-Status: >> >> This is not true... Looks like you will have to look further in to >> what astigmatism is. > >Thanks for your correction, but... > >it wasn't clear to me exactly WHAT was not true in what I said. Can you >point out to me exactly what parts of my original post were in error? > >--Alex Hi, This is your statement: Also, if you improve your ability to accommodate (adjust for distance) -- the astigmatism will diminish somewhat. Hence my explanation. In discussing patient's visual problems with them, astimatism is one of the hardest concepts for patients to grasp. They almost always, in later discussions, talk of it as if it were some terrible condition, that their eye has "a stigmatism," and are always vague about what exactly a stigmatism is (such as if it is some communicable disease). Even a mild amount of astigmatism (especially if the axis is at ninety degrees (known as against-the-rule, because most is at 180 degrees, or with-the-rule) can cause asthenopia (eye strain symptoms), as the accommodation control system is a bit spun out by the two line foci, and doesn't know where to focus to. Printed text has a strong vertical bias, so it is not necessarily best to focus the circle of least confusion on the retina. Cheers! ''' (0 0) +----oOO----(_)-----------+ | Rene Malingre | | R.Malingre@qut.edu.au | +------------------oOO----+ |__|__| || || ooO Ooo ========================================================================= From usenet.ucs.indiana.edu Sun Mar 19 08:12:19 1995 From: Ted_Landis@BendNet.Com Newsgroups: sci.optics Subject: Astigmatism Date: 17 Mar 1995 17:40:48 GMT Organization: RGNet I just got some new glasses and I'd like a second opinion. My old glasses didn't have any correction for astigmatism. The doctor now says that I have an astigmatism in both eyes, a little in the right and a lot in the left. I got my new glasses and now, while everything is very sharp, all rectangular objects look like sideways trapazoids! If I look at a rectangle on my computer screen, the left side is about 10% longer than the right side, and the top and bottom lines flow up and down respectively. The doctor says that this is something that I will get used to and that within a week or so, my brain will adjust the image so that I don't notice it anymore. While my brain may be able to adjust, I don't know if I want it to. Is this really just a case of over correction of an astigmatism? Anyone have an opinion? BTW, the primary purpose of the glasses is to correct my nearsightedness. Thanks for any help, Ted ========================================================================= From owner-i_see@indiana.edu Mon Jul 10 14:45:32 EST 1995 Date: Mon, 10 Jul 95 12:41 PDT From: Robert_Michael_Kaplan@Sunshine.net (Robert-Michael Kaplan) Subject: Re: Decreasing prescription strength in Myopia Status: RO X-Status: Alex at I_SEE wrote: >And, while I'm here, I've got another question: can you explain your >theory behind overcorrecting astigmatism? This strikes me as very weird, >since all my favorite authors (Kennebeck, Raphaelson, Prentice, Simpkins) >are adamantly opposed to cylinders. This is a very difficult question to answer in a short form. I'll give a try, otherwise when we work together, I 'll teach you the mechanics. By definition, astigmatism means one area of space is more blurry than another. The seperation is usually by 90 degrees. In the simplest example, the vertical meridian of the cornea would show more myopia than its horizontal counterpoint. Here is the essence. The person's learning is to begin to see through the vertical meridian. This is the area of space that is the most blurry, and represents the most blurriness in their life. In later discussions, I 'll demonstrate that the vertical meridian has particular psycho-emotional correlates. If my hypothesis is correct, then the lens the person looks through, should accentuate light focusing more on the vertical meridian than the horizontal. The only way this can be accomplished is to increase the astigmatism for myopia, although we can reduce the astigmatism in farsightedness. If you just leave out the cylinder, then the person learns to see more clearly through the horizontal in this example. Granted their eyesight may improve, howeer, their discovery of the learning they need to get to the cause of the problem is never addressed. This is the distinction between integrated vision therapy and say regular vision therapy or even vision improvement. Phew, that does it for now. All the best, Robert-Michael. ========================================================================= From roosen@cts.com Sat Aug 26 22:16:42 EST 1995 Date: Sat, 26 Aug 1995 20:16:36 -0700 (PDT) From: Robert Roosen Subject: Re: Astigmatism and head tilt Status: RO X-Status: On Sat, 26 Aug 1995, Alex Eulenberg wrote: > If you wear glasses for astigmatism, what happens when you tilt your > head? Do things get more or less blurry, or do they stay the same? I have pretty good astigmatism. When I tilt my head up wearing computer glasses the screen seems to become more out of focus. Tilting down does not go through as much of an angle, so will not comment on that. Robert ========================================================================= From asirohi@Glue.umd.edu Mon Aug 28 07:53:29 EST 1995 From: Ashuraj Sirohi Date: Mon, 28 Aug 1995 08:53:24 -0400 Subject: Re: Astigmatism and head tilt Status: RO X-Status: > Hi folks! I've started an uproar on sci.med.vision about astigmatism. I > said that if you tilt your head wearing astigmatic glasses, the glasses > no longer work the same, since your eyes rotate to keep straight-up. > > This statement was based on hearsay, things I read, and common sense. I > never wore glasses for astigmatism. Can any people with astigmatism vouch > for (or against?) me on this? > > If you wear glasses for astigmatism, what happens when you tilt your > head? Do things get more or less blurry, or do they stay the same? I have very low astigmatism (-0.5,-0.5, 100 axis in both eyes). If I stand straight and rotate the lenses in front of eyes i can see the letters get blurry on the eye chart, precisely the reason why I have 100 degree axis correction. Wearing the glasses and tilting my head on either side does not make any difference to me. Well! if that made objects blurry then why get astigmatic correction at all. -ashu ========================================================================= From JimDayOD@aol.com Sun Sep 3 23:31:16 EST 1995 From: JimDayOD@aol.com Date: Mon, 4 Sep 1995 00:30:00 -0400 Subject: Re: Astigmatism and head tilt Status: RO X-Status: Alex, It is a FACT that your eyes rotate and it does change your vision thru glasses. As my personal problem is hyperopic astigmatism. I can rotate my head and see a definite change. However, binocular fusion tends to correct for the error. Untreated vertical deviations aggravate the problem since they tend to cause head tilt in many cases. Vertical deviations will can cause the neck strain you describe much more often. It can also cause slow reading, headaches, backache, motion sickness, and neck pain. They are a common problem. Since they cause slow reading and headaches looking at a computer, every patient should be carefully checked for vertical deviations, especially if head tilts improve or blur vision. Blur on head tilt is easy to demonstrate, cover one eye to break fusion, tilt your head until blur is noticed. Clinically, you will find more or less equal tilt right to left with each eye. Unequal tilt can be a sign of problems in the correction worn. This effect is power related, large astigmatic cases or greater vertical hyperphoria will have more noticable changes, tilts and errors. The most accurate procedure, Binocular Fusion during refraction, is not common in OD's procedures. It is very rare, if ever, done in Ophthalmology practice. Common methods to discuss with your eye care provider: TIB, Turner Infinity Balance is used at UAB with mirrors, each eye sees half the chart. The American Optical Vectographic chart uses polarized, "3D", each eye can see every other letter. It is found at any office that provides binocular vision analysis. I think its all the more reason to get an annual professional eye examination that includes binocular vision analysis. Jim Day, Jr OD Member National Eye Research Foundation ========================================================================= From owner-i_see@indiana.edu Fri Dec 1 18:09:10 EST 1995 Date: Fri, 1 Dec 1995 17:54:35 -0500 (EST) From: Alex Eulenberg Subject: Re: Do I have myopia or stigmatism? Status: RO X-Status: On Thu, 30 Nov 1995, Torres Mario wrote: > How can I know which category does my poor eyesight belong > in? myopia or stigmatic? First of all, the word is "astigmatism", which comes from greek "a" without + "stigma" = point. So etymolgically it just means "unfocused". Now then. Myopia means that your eye is incapable of adjusting for faraway objects. The image is projected IN FRONT OF the retina (Hyperopia or presbyopia means that the image is projected in back of the retina for near objects. Yes it does sound counterintuitive, but that's just the laws of optics. With a lens of a given power, near objects are projected so that the screen should be further from the lens, and for farther objects, the screen should be nearer.) In other words, if your retina could be moved up closer to the lens, or if the object were moved closer, the image would be in focus. Astigmatism means a slight "extra" curvature in the lens or cornea to make the refracting surface non-spherical. The result is that no matter where you move the retina (if you could), or no matter where you move the object, it will be out of focus. Another side effect of astigmatism is multiple images in one eye, especially from luminous objects like the moon. For many people, the effects of astigmatism are different at different distances. It is possible to have both myopia and astigmatism. It is also possible to reduce or cure both myopia and astigmatism, by putting your mind into a state of restful alertness, by relaxing the muscles of the eyes, face, and neck, and by keeping the mind, eye, and body mobile, as opposed to tense, strained, and worried. Body affects mind and mind body. More specific suggestions as to how to do this coming up! Stay tuned! Or, if you have your own favorite mind and/or body relaxation techniques, please post them to I_SEE. --Alex =========================================================================