 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Medical Forum / General / Vision / November 2004Unable to correct to 20/20
I recently had an (eyeglass) exam and was told that the best that I could be corrected to in one eye was 20/25 or so, that my eye would not accept enough correction. The suggested lens i -1 with slight astigmatism. (My other eye can be brought to 20/15). I don't understand. My limited understanding of optics says it should be correctable. Why not?? >I recently had an (eyeglass) exam and was told that the best that I > could be corrected to in one eye was 20/25 or so, that my eye would [quoted text clipped - 3 lines] > I don't understand. My limited understanding of optics says it should > be correctable. Why not?? There is usually a reason, but it isn't always detectable in a routine eye exam. If you can see better than 20/25 through a pinhole, then the refraction is off, or there's some irregularity in the shape of your cornea that can't be corrected with lenses, like a subtle distortion from corneal dystrophy. Small corneal scars and early cataracts can limit vision in subtle ways. These are usually detectable with the slit lamp microscope. Sometimes vitreous floaters obscure your vision, existing as faint sheets or veils that aren't obvious, even with a dilated examination. Mild macular edema, early retinal gliosis, and subtle optic nerve disease can be difficult to see in a quick examination. Presumably your doctor found no explanation, or he would have told you. You could pursue another eye examination and mention this problem as your chief complaint. But most of the problems mentioned above have no specific treatment. The first thing is to compare your vision with your spectacle lens to the vision you get through a pinhole. If the pinhole is better for small details far away, consider going back for a repeat of the refraction. -MT, OD > I recently had an (eyeglass) exam and was told that the best that I > could be corrected to in one eye was 20/25 or so, that my eye would [quoted text clipped - 3 lines] > I don't understand. My limited understanding of optics says it should > be correctable. Why not?? 20/20 is an statistical norm for human vision, not an objective determination of perfect vision. Some people can be corrected to better than 20/20 and some worse than 20/20. It has more to do with biology than physics, since you are merely comparing your vision to the average of other humans. Does that imply that the resolution of the retina is "poor"? After all, a lens can be made to properly focus on an object. >> I recently had an (eyeglass) exam and was told that the best that I >> could be corrected to in one eye was 20/25 or so, that my eye would [quoted text clipped - 9 lines] >physics, since you are merely comparing your vision to the average of other >humans. > Does that imply that the resolution of the retina is "poor"? After > all, a lens can be made to properly focus on an object. When you look at an eye chart, your eyes can be properly focused on all the lines, but each person can only see lines that are large enough for them to make out. At some point the lines are too small for anyone to see. This limitation is not related to focus, although if your vision were not corrected properly and you had a focusing problem, that would make it worse. > Does that imply that the resolution of the retina is "poor"? After > all, a lens can be made to properly focus on an object. That is not quite true. Ordinary lenses will correct for focus and astigmatism and possible prism. In most cases that is good enough. But as Mike Tyner pointed out, cataracts and other defects may produce more random errors not easily corrected. These are often called higher order aberrations. The new wavefront lasik can, in principle, correct for some of these errors. In the optics of lenses rather than eyes, that process is called *figuring*. That is how the Hubble telescope was saved But that has many limitations as well. These include additional aberrations introduced if you are not looking in the design's direction. When I had a cataract, my crystalline lens was granular even though it was still reasonably transparent. My biggest problem came from multiple images produced by these granularities. There is no practical way to correct vision defects arising from such defects. The corrective lens, even if it is a shaping of the cornea is too far away from the defect to compensate accurately. I am not a health professional. Bill It is also possible that the image is correctly focused on the retina, yet the brain does not process the information to that level of detail. This happens in amblyopes. You can have an eye with 20/20 optics yet the brain does not perceive that level of detail due to suppression or other neuropsychological reasons. ---- > Does that imply that the resolution of the retina is "poor"? After > all, a lens can be made to properly focus on an object. [quoted text clipped - 14 lines] >>other >>humans. Dear Friend, In general I believe that "amblyopia" is defined as an eye that can not be "corrected" to 20/20. I further believe that this is "genetic", in the fact that the situation is found with one or two eyes. Once you have it, you can not get rid of it. If you previously had 20/20, and now 20/25 then the reasons are not genetic. Best, Otis Engineer > It is also possible that the image is correctly focused on the retina, yet > the brain does not process the information to that level of detail. This [quoted text clipped - 22 lines] > >>other > >>humans. > In general I believe that "amblyopia" is defined > as an eye that can not be "corrected" to 20/20. If you're lecturing us on medical conditions, you might want to get it right. Amblyopia is clinically defined as vision that cannot be corrected to 20/20 *in the absence of detectable pathology.* > I further believe that this is "genetic", in > the fact that the situation is found with > one or two eyes. Expounding your beliefs again, rather than facts. Amblopia is neither genetic nor congenital. It is seldom found in both eyes, but when it is, toxicity or other bilateral causes are usually present. >Once you have it, you > can not get rid of it. Should we should stop treating it because you believe it can't be treated? > If you previously had 20/20, and now 20/25 > then the reasons are not genetic. Corneal dystrophies are genetic. Keratoconus is genetic. Many other genetic conditions produce mild distortions of vision. -MT > I further believe that this (i.e. amblyopia) is "genetic", Wrong! > If you previously had 20/20, and now 20/25 > then the reasons are not genetic. Really, there are genetic eye disorders that result in diminished acuity over time. I guess they didn't teach you that in engineering school. But isn't that the point anyway-- what kind of training or experience do you have that qualifies you to give people advise about vision problems!! Go design a better vacuum cleaner. Any you won't find me or any other eyecare professional posting advise to you in the newsgroup alt.engineering.vacuum !! ============ > Best, > [quoted text clipped - 30 lines] >> >>other >> >>humans. Dear no-name, I made a statement about how amblyopia was determined. There are other MEDICAL situations that indeed prevent a lens from producing 20/20 -- even though the image is sharp on the retina. Since we don't know who you are, the people can take your statement for what it is worth. Further, making a stement IS NOT PROVIDING MEDICAL ADVICE, NOR IS ANY ACTION TO BE TAKEN ON THE BASIS OF MY STATEMENT. Best, Otis Engineer > > I further believe that this (i.e. amblyopia) is "genetic", > [quoted text clipped - 50 lines] > >> >>other > >> >>humans. Readers please note: Otis Brown posts his ridiculous, unsupported theory to this newsgroup over and over again, day after day. Over a thousand times thus far. Numerous doctor practitioners and vision scientists have clearly and precisely debunked his argument, yet he persists in trying to attract the gullible. That which those of us with vision science background post here is based on proven, tested repeatable, clinically observed (thousands if not hundreds of thousands of times) real data. This is very much unlike "Otis", who invents theories, creates terminology to fit it, and "reports" "findings" based on two individuals who may or may not exist. Please do not reply to "Otis" posts. Please see the weekly posting "welcome to sci.med.vision" which appears on Mondays for information on how to filter out his posts so that you may be able to participate in worthwhile discussion in this forum. Thank you for your cooperation and understanding. > Dear Friend, > [quoted text clipped - 8 lines] > If you previously had 20/20, and now 20/25 > then the reasons are not genetic. I believe that this post exactly exemplifies the posts that Otis makes to this group. He relies on a belief system (see the word "believe" in the first two paragraphs). Scientific fact is accepted as long as it supports his beliefs. If it doesn't, then it is irrelevant. Where he doesn't have beliefs or knowledge, then he just makes stuff up (the third paragraph).  SignatureDan Abel Sonoma State University AIS dabel@sonic.net > It is also possible that the image is correctly focused on the retina, yet > the brain does not process the information to that level of detail. This > happens in amblyopes. You can have an eye with 20/20 optics yet the brain > does not perceive that level of detail due to suppression or other > neuropsychological reasons. Wow, what a real interesting statement!!! |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.