Does Astigmatism literally mean that someone cannot resolve/discern a stigmatic image naturally? And is it even humanly possible to see a stigmatic image?
I guess there may be some truth to the guy who says "I got stigmatism!"
Does Astigmatism literally mean that someone cannot resolve/discern a stigmatic image naturally? And is it even humanly possible to see a stigmatic image?
I guess there may be some truth to the guy who says "I got stigmatism!"
http://www.yourdictionary.com/astigmatism
a-without
stigma- from Greek- point (specific focal))
ism- from Latin- distinctive or characteristic trait
Last edited by Uncle Fester; 12-19-2014 at 04:16 PM.
Too vagueOriginally Posted by Uncle Fester
says the guy with 13 posts to the guy who has 3,371 posts...
..
astigmatism |əˈstigməˌtizəm|
noun
a defect in the eye or in a lens caused by a deviation from spherical curvature, which results in distorted images, as light rays are prevented from meeting at a common focus.
DERIVATIVES
astigmatic |ˌastigˈmatik|adjective
ORIGIN mid 19th cent.: from a-1‘without’ + Greek stigma ‘point’ +-ism.
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No, it means that rays of light entering the eye do not come to a single point of focus.
"Some eyes have two different curves on a single refracting surface on or within the eye. This is known as astigmatism." -System for Ophthalmic Dispensing, Brooks and Borish, 2nd ed.
I know there is the 3rd edition out, but I seriously doubt that the definition has changed. And if you're not going to accept Fester's etymological definition, then I'm not sure what you mean by "literally mean" since that's what he gave you.
I suppose a better name might be ocular aspherism, meaning the eye is not a sphere.
There are rules. Knowing those are easy. There are exceptions to the rules. Knowing those are easy. Knowing when to use them is slightly less easy. There are exceptions to the exceptions. Knowing those is a little more tricky, and know when to use those is even more so. Our industry is FULL of all of the above.
THE NONSTIGMATIC IMAGE The preceding treatment deals primarily with two image characteristics: location and size. This and the following three sections deal with image quality. An image is never a perfect scale duplicate of the object, exact in every detail. A certain loss of detail is inherent in the imaging process. At best, an image is an imperfect facsimile of the original object.The loss of detail occurs because images are not stigmatic. The stigmatic image is an idealization that cannot be achieved. Light from an object point does not come to a perfect point focus. Instead, light from a single object point is distributed over a small but definite area of the image. The light may spread over a region as small as a few microns in diameter or as large as 100 μm (0.1 mm) in diameter.
I guess I am trying to spark a little more discussion about Astigmatism rather than just giving the "Lenscrafters new optician 101" definition of what Astigmatism is.
So, staying with that ... If someone does NOT have Astigmatism, (not being able to discern a stigmatic image -- which cannot be achieved by humans) does that make them Stigmatic by default?-- Even though it has been stated that humans cannot resolve perfect stigmatic images.
I think most of you are just explaining what Astigmatism is as a refractive error and how it is generally resolved (cylinders/axes and what have you)
Last edited by NMoptic; 12-19-2014 at 01:18 PM.
https://books.google.com/books?id=uE...matism&f=false
Click below to download a power point presentation on astigmatism.
Astigmatism
http://www.highburyeye.co.nz/images/highbury/astigmatism.gif
Deeper.
http://cdn.intechopen.com/pdfs-wm/29984.pdf
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
I guess that would lead me to say that ALL humans have Astigmatism: Given that it is impossible for humans to see a perfect stigmatic image.
It depends on where you draw the line. Most OD's/MD's I've dealt with it's at +/-0.25 diopters (or more precisely: between +0.124 and -0.124 diopters, the correction is 0.00, outside of that, it is rounded to the nearest 0.25 (OD) 0.12 (MD) [at least in my experience LOL])
What is this taken from?
There are rules. Knowing those are easy. There are exceptions to the rules. Knowing those are easy. Knowing when to use them is slightly less easy. There are exceptions to the exceptions. Knowing those is a little more tricky, and know when to use those is even more so. Our industry is FULL of all of the above.
http://www.eyecalcs.com/DWAN/pages/v1/v1c030.html#then
Mostly a disscusion of non-ophthalmic lens systems.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Eyecalcs
I love that last link... Thank you so much....I like how it goes into detail about the disc of least confusion....
And then combine that with asphericity and aberrations http://en.wikipedia.org/wiki/Optical_aberration
And, when it comes to eyeglass Rxs, it is always about "net" astigmatism.
B
I got stigmuhtism
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