3 ms·

No conspiracy theory was claimed. Here's one of the newer summaries of research on prisms for convergence issues, unfortunately in German, but the abstracts' in

No conspiracy theory was claimed. Here's one of the newer summaries of research on prisms for convergence issues, unfortunately in German, but the abstracts' in English: https://link.springer.com/article/10.1007/s00347-014-3037-9 https://link.springer.com/article/10.1007/s00347-014-3037-9 Which states quite clearly that horizontal prisms shouldn't get prescribed, only vertical prisms, and weaker ones than previously thought, which brings us right back to the fact that we need more competent developmental, behavioral functional optometry & orthopty. Furthermore, you probably want to read this article by Rodenstock: http://assets.markallengroup.com/article-images/image-library/147/uploads/importedimages/20rodenstock.pdf http://assets.markallengroup.com/article-images/image-librar... It's unfortunately marketing material, however, it's also the only English resource I know that outlines the problems of: * Listing's law in its original version only applying to distance vision * 'effective near astigmatism' * tilting of the intraocular lens inside one document so you don't have to go crawling all over the literature to find them like I had to. Now think of how failing to properly correcting that influences accommodative strabismus via the accommodation-convergence reflex in anisometropic patients... Especially if the glasses ain't iseikonic and thus induce unwanted and unbalanced base in/base out prism. Of course, Rodenstock has a patent on some of these corrections. While Hoya has a patent on freeform double surface lenses which makes everything way more complicated to optimize when you ain't Hoya, Zeiss has a patent on knocking out convergence using an infrared light source to measure pupil position, and on various multiphoton raytracing technologies for calculating corrections such as the one Rodenstock describes (leading to Rodenstock using a complicated workaround), and so on, dozens of patents locking everyone out of making an /optimal/ pair of glasses. Yes this makes all vendors about equally good, but only by making all of them, relatively speaking, mediocre. Each in their own special way. And don't get me started up on contact lenses and how they relate to the difference between axial anisometropia, refractive anisometropia, and their hybrid. My point here, and in my other comments (https://news.ycombinator.com/item?id=16195742 https://news.ycombinator.com/item?id=16195742 & https://news.ycombinator.com/item?id=16195570 https://news.ycombinator.com/item?id=16195570): There exists no conspiracy. There only exists cock-up, and lots of it. Hanlon's razor etc.

walterbell 9y ago
What are your thoughts on causes/treatment of astigmatism? Could lens distortion (away from optical center of a high minus lens) be a contributing factor over a long period of time? If so, could be an argument for using FF lenses. Apparently the Zeiss FF patent expired this month and Seiko's FF patent expired in 2016. Rodenstock lenses are not widely available in the US. Looks like the Zeiss Individual SV will compensate for astigmatism caused by pantoscopic tilt, https://pdfs.semanticscholar.org/3e73/2da37ec9e17bd086b32095c57bc9ab5b6ce3.pdf https://pdfs.semanticscholar.org/3e73/2da37ec9e17bd086b32095... Some quotes from Chapter 1 of an open-access book on astigmatism: https://www.intechopen.com/books/astigmatism-optics-physiology-and-management https://www.intechopen.com/books/astigmatism-optics-physiolo... … visual tasks with significant downward gaze, such as reading, can alter corneal curvature owing to eyelid pressure ... Studies on the time course of astigmatism regression have revealed slower recovery after longer periods of reading ... continuous use of the medial rectus muscle, especially during near tasks, imposes a force on the cornea which increases its radius of curvature in the horizontal meridian resulting in a shift towards against-the-rule astigmatism... … Larger pupil sizes—in low lighting conditions— increase the amount of higher order aberrations such as coma and may intensify the cylinder power in subjective/manifest refraction. Coma has been shown to be correlated with greater amounts of astigmatism … … accommodative astigmatism is related to lens distortion due to inhomogeneous lens elasticity, variable constriction in ciliary muscles (which itself changes the lens power), and nonhomogeneous tension of the extraocular muscles during convergence (which causes corneal distortion… … slight changes in cylinder power and axis (towards with the rule) occur during convergence alone … this change is seen in a small percentage of eyes … for those who experience such an alteration, separate spectacle prescriptions for near and far distance vision might be beneficial.
- no_identd 9y ago
  >What are your thoughts on causes/treatment of astigmatism? Could lens distortion (away from optical center of a high minus lens) be a contributing factor over a long period of time? If so, could be an argument for using FF lenses. Apparently the Zeiss FF patent expired this month and Seiko's FF patent expired in 2016. Pfuuuh. Got a link? I honestly have to say I draw a blank in regards to what you mean by "FF lenses", as I'd assume you wouldn't mean full frame lenses in the photography sense? >Rodenstock lenses are not widely available in the US. I know. They recently made an attempt to relaunch in the US but I have no idea if it succeeded. >Looks like the Zeiss Individual SV will compensate for astigmatism caused by pantoscopic tilt, https://pdfs.semanticscholar.org/3e73/2da37ec9e17bd086b32095.. https://pdfs.semanticscholar.org/3e73/2da37ec9e17bd086b32095.... Yepp, but that's not the main problem. The main problem comes from the cyclotorsion the eyes exhibit during convergence as part of the donward gaze. This fundamentally changes the astigmatism axis. I didn't go into this in my earlier post (Which I'll link here, since it's in a different sub-thread: https://news.ycombinator.com/item?id=16195742 https://news.ycombinator.com/item?id=16195742), but actually, to expand on this, I consider cyclotorsion a HUGE problem in the successful measurement of astigmatism. I've tested this empirically quite a few times, and the traditional cover test fails to fully interrupt the fusional circuit in the brain, the cyclotorsion component remains active until the other eye is closed consciously. (In fact, I speculate that even then it remains partially active, and in some cases only a temporary concious supression of the [inside-of-your-eyelids] image leads to a full disengagement of the circuit. But this is highly speculative, take this part with a large grain of salt.) I consider this a problem because: 1. Cycloplegia in fact fails to prevent cyclotorsional adjustment. 2. Incorrect astigmatism correction can lead to amblyopic suppression, which can lead to (micro)strabismus, which leads to diplopia. Now, horizontal prisms aside, which we shouldN't prescribe, ever, except in EXTREMELY rare cases of total muscle paralysis or similar, this can then lead to an incorrect measurement of vertical deviation of the angle of gaze, which leads to an incorrect prism prescription, which... well, you get the point. Bonus if the astigmatism correction ends up so off, you end up affecting distance vision and cause accommodation. Double bonus if the patient already suffered from accommodative cramps [which btw. WON'T GET ANY BETTER if we keep the testing distance at 6 meters, which as, previously state, definitely DOESN'T equal optical infinity.]. Triple bonus if they didn't get cycloplegia to compensate for it at first. Quadruple bonus if the pupil dilation from the cycloplegia fucks up the astigmatism measurement [which is the point where wavefront measurements shine, because they can backinfere about the behavior of the narrower pupil even from the measurement of the widened pupil! But even wavefront measurement can't compensate for cyclotorsion! But of course that gets fucked up by wavefront mesurements that fail to consider the full pupil diameter!] >Some quotes from Chapter 1 of an open-access book on astigmatism: https://www.intechopen.com/books/astigmatism-optics-physiolo.. https://www.intechopen.com/books/astigmatism-optics-physiolo.... >continuous use of the medial rectus muscle, especially during near tasks, imposes a force on the cornea which increases its radius of curvature in the horizontal meridian resulting in a shift towards against-the-rule astigmatism... Interesting. Didn't know that one yet. > Larger pupil sizes—in low lighting conditions— increase the amount of higher order aberrations such as coma and may intensify the cylinder power in subjective/manifest refraction. Coma has been shown to be correlated with greater amounts of astigmatism Yepp, see my point about wavefront measurements. >accommodative astigmatism is related to lens distortion due to inhomogeneous lens elasticity, variable constriction in ciliary muscles (which itself changes the lens power), and nonhomogeneous tension of the extraocular muscles during convergence (which causes corneal distortion… True, but this ignores the cyclotorsional element. >slight changes in cylinder power and axis (towards with the rule) occur during convergence alone … this change is seen in a small percentage of eyes Small percentage my ass, that's a case of underdiagnosis due to insufficiently precise measuring equipment. >for those who experience such an alteration, separate spectacle prescriptions for near and far distance vision might be beneficial. or we can just, I don't know, PROGRESSIVELY ALTER THE ASTIGMATISM CORRECTION AS PART OF GLASSES? Using the same technology we already use for progressives? I know, I know, that'd seem TOO LOGICAL. Sorry, I harbor the most bitter feelings on this topic.

walterbell 9y ago

What are your thoughts on causes/treatment of astigmatism? Could lens distortion (away from optical center of a high minus lens) be a contributing factor over a long period of time? If so, could be an argument for using FF lenses. Apparently the Zeiss FF patent expired this month and Seiko's FF patent expired in 2016. Rodenstock lenses are not widely available in the US. Looks like the Zeiss Individual SV will compensate for astigmatism caused by pantoscopic tilt, https://pdfs.semanticscholar.org/3e73/2da37ec9e17bd086b32095c57bc9ab5b6ce3.pdf https://pdfs.semanticscholar.org/3e73/2da37ec9e17bd086b32095... Some quotes from Chapter 1 of an open-access book on astigmatism: https://www.intechopen.com/books/astigmatism-optics-physiology-and-management https://www.intechopen.com/books/astigmatism-optics-physiolo... … visual tasks with significant downward gaze, such as reading, can alter corneal curvature owing to eyelid pressure ... Studies on the time course of astigmatism regression have revealed slower recovery after longer periods of reading ... continuous use of the medial rectus muscle, especially during near tasks, imposes a force on the cornea which increases its radius of curvature in the horizontal meridian resulting in a shift towards against-the-rule astigmatism... … Larger pupil sizes—in low lighting conditions— increase the amount of higher order aberrations such as coma and may intensify the cylinder power in subjective/manifest refraction. Coma has been shown to be correlated with greater amounts of astigmatism … … accommodative astigmatism is related to lens distortion due to inhomogeneous lens elasticity, variable constriction in ciliary muscles (which itself changes the lens power), and nonhomogeneous tension of the extraocular muscles during convergence (which causes corneal distortion… … slight changes in cylinder power and axis (towards with the rule) occur during convergence alone … this change is seen in a small percentage of eyes … for those who experience such an alteration, separate spectacle prescriptions for near and far distance vision might be beneficial.

no_identd 9y ago
>What are your thoughts on causes/treatment of astigmatism? Could lens distortion (away from optical center of a high minus lens) be a contributing factor over a long period of time? If so, could be an argument for using FF lenses. Apparently the Zeiss FF patent expired this month and Seiko's FF patent expired in 2016. Pfuuuh. Got a link? I honestly have to say I draw a blank in regards to what you mean by "FF lenses", as I'd assume you wouldn't mean full frame lenses in the photography sense? >Rodenstock lenses are not widely available in the US. I know. They recently made an attempt to relaunch in the US but I have no idea if it succeeded. >Looks like the Zeiss Individual SV will compensate for astigmatism caused by pantoscopic tilt, https://pdfs.semanticscholar.org/3e73/2da37ec9e17bd086b32095.. https://pdfs.semanticscholar.org/3e73/2da37ec9e17bd086b32095.... Yepp, but that's not the main problem. The main problem comes from the cyclotorsion the eyes exhibit during convergence as part of the donward gaze. This fundamentally changes the astigmatism axis. I didn't go into this in my earlier post (Which I'll link here, since it's in a different sub-thread: https://news.ycombinator.com/item?id=16195742 https://news.ycombinator.com/item?id=16195742), but actually, to expand on this, I consider cyclotorsion a HUGE problem in the successful measurement of astigmatism. I've tested this empirically quite a few times, and the traditional cover test fails to fully interrupt the fusional circuit in the brain, the cyclotorsion component remains active until the other eye is closed consciously. (In fact, I speculate that even then it remains partially active, and in some cases only a temporary concious supression of the [inside-of-your-eyelids] image leads to a full disengagement of the circuit. But this is highly speculative, take this part with a large grain of salt.) I consider this a problem because: 1. Cycloplegia in fact fails to prevent cyclotorsional adjustment. 2. Incorrect astigmatism correction can lead to amblyopic suppression, which can lead to (micro)strabismus, which leads to diplopia. Now, horizontal prisms aside, which we shouldN't prescribe, ever, except in EXTREMELY rare cases of total muscle paralysis or similar, this can then lead to an incorrect measurement of vertical deviation of the angle of gaze, which leads to an incorrect prism prescription, which... well, you get the point. Bonus if the astigmatism correction ends up so off, you end up affecting distance vision and cause accommodation. Double bonus if the patient already suffered from accommodative cramps [which btw. WON'T GET ANY BETTER if we keep the testing distance at 6 meters, which as, previously state, definitely DOESN'T equal optical infinity.]. Triple bonus if they didn't get cycloplegia to compensate for it at first. Quadruple bonus if the pupil dilation from the cycloplegia fucks up the astigmatism measurement [which is the point where wavefront measurements shine, because they can backinfere about the behavior of the narrower pupil even from the measurement of the widened pupil! But even wavefront measurement can't compensate for cyclotorsion! But of course that gets fucked up by wavefront mesurements that fail to consider the full pupil diameter!] >Some quotes from Chapter 1 of an open-access book on astigmatism: https://www.intechopen.com/books/astigmatism-optics-physiolo.. https://www.intechopen.com/books/astigmatism-optics-physiolo.... >continuous use of the medial rectus muscle, especially during near tasks, imposes a force on the cornea which increases its radius of curvature in the horizontal meridian resulting in a shift towards against-the-rule astigmatism... Interesting. Didn't know that one yet. > Larger pupil sizes—in low lighting conditions— increase the amount of higher order aberrations such as coma and may intensify the cylinder power in subjective/manifest refraction. Coma has been shown to be correlated with greater amounts of astigmatism Yepp, see my point about wavefront measurements. >accommodative astigmatism is related to lens distortion due to inhomogeneous lens elasticity, variable constriction in ciliary muscles (which itself changes the lens power), and nonhomogeneous tension of the extraocular muscles during convergence (which causes corneal distortion… True, but this ignores the cyclotorsional element. >slight changes in cylinder power and axis (towards with the rule) occur during convergence alone … this change is seen in a small percentage of eyes Small percentage my ass, that's a case of underdiagnosis due to insufficiently precise measuring equipment. >for those who experience such an alteration, separate spectacle prescriptions for near and far distance vision might be beneficial. or we can just, I don't know, PROGRESSIVELY ALTER THE ASTIGMATISM CORRECTION AS PART OF GLASSES? Using the same technology we already use for progressives? I know, I know, that'd seem TOO LOGICAL. Sorry, I harbor the most bitter feelings on this topic.