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Medical Forum / General / Vision / March 2009Seeing Rainbows?
Hi, I have grown up since I first wore glasses 6 years ago. I still have the same -3.0 eyes. I heard that if the PD of the eyes don't match the OC (as my PD got wider), there would be prismatic effect. What is prismatic effect? Does it involve seeing rainbows? If my eyes PD now is 70 from 65 five years ago. Would the mismatch cause increase minus powers in the glasses? Would my -2.0 become a -2.25 when PD and OC differs by 5mm? I want to stay as much as possible with my glasses if it won't change the power because I don't have money to buy a new one. I don't mind seeing rainbows. Willy Sylers In article <ae8cfd33-0163-46c4-9749-6509a3db4e62@s38g2000prg.googlegroups.com>, > Hi, > [quoted text clipped - 10 lines] > > Willy Sylers In addition to any lens power, labelled spherical on a prescription, there can be the equivalent of a prism added to the lens. This prism means that your line of sight is deviated a bet by the amount and orientation of the prism. I like to use the term "optical wedge" so as to imply only a small prism deflection. It turns out that if you do not look directly through the center of a rotationally symmetric lens, your line of sight gets deviated also. Thus. how you edge a lens to fit into a set of frames can affect how much deviation you get. This requires you optometrist to take centering into account, Bill  SignaturePrivate Profit; Public Poop! Avoid collateral windfall! > In article > <ae8cfd33-0163-46c4-9749-6509a3db4...@s38g2000prg.googlegroups.com>, [quoted text clipped - 30 lines] > -- > Private Profit; Public Poop! Avoid collateral windfall! I heard of the Prentice Rule wherein the prism diopter is equal to the lens power in diopters multipy by difference between PD and OC. In my case where my lens power is -2.0 and difference is 5mm or 0.5 cm Prentice Rule OD -2.0 x 0.5cm = 1.0 prism diopter What is the relevance of the 1.0 prism diopter, how does it convert back to lens power or do you just add -2.0 to -1.0 = -3.0 meaning if my PD differs from the glasses OC by 5mm. The power would of the decentering view become -3.0? But I don't see the image blurer. Perhaps 1.0 prism diopter is equal to say 0.15 D in lens power so you add -2.0 to -0.15 D to become -2.15D? Willy Sylers -SNIP- > I want to stay as much as possible > with my glasses if it won't change the power because I don't > have money to buy a new one. I don't mind seeing rainbows. > > Willy Sylers Willy, You just might be suprised about how much money you'd need to buy new ones. Is approx. $8.00 to $30.00 to expensive for you? If that has piqued your interest, come join us over at http://groups.google.com/group/glassyeyes?hl=en and talk with others who thought glasses had to cost $300 to $500 just for simple prescriptions. -=# Firewalker #=- > -SNIP- > [quoted text clipped - 12 lines] > > -=# Firewalker #=- My original glasses have sentimental value and the only defect of it is 5mm off center. Do you know what is the relationship between prismatic diopter and lens power diopter? How much lens power diopter is 1.0 prismatic diopter equal to? Willy It's two different "prismatic" effects. Ond effect is to displace the image laterally. The other is to break white light into rainbows. Prisms do both. Misplaced PD causes very small prism angles, and slight image displacement. Normally rainbows require very large angles. -MT > Hi, > [quoted text clipped - 10 lines] > > Willy Sylers > It's two different "prismatic" effects. > > Ond effect is to displace the image laterally. Displacing the image laterally won't create any distortion at all as its like the images you see is all shifted 5mm to the right or left. So eyeglasses OC doesn't have to match the PD at all. Is that correct? Or would the images you see displaced laterally mean they are compressed to the center in the spectacles nose bridge? Willy > The other is to break white light into rainbows. > [quoted text clipped - 22 lines] > > - Show quoted text - the right or left. So eyeglasses OC doesn't have to match the PD at all. Is that correct? Horizontally you can tolerate a lot of error in the OCs. Vertically it only takes a little to drive you nuts. > Or would the images you see > displaced laterally mean they are compressed to the > center in the spectacles nose bridge? You described glasses made too wide, using 5mm of extra PD and I thought it was -3.00 so I figured 1/2cm x 3 = 1.5 prism diopters (base-in). In the horizontal direction, that's almost negligible. Vertical is another story. 1.5 prism diopters base-up or base-down would be an instant headache. > > If my eyes PD now is 70 from 65 five > > years ago. I'd have a CT scan right away. -MT > the right or left. So eyeglasses OC doesn't have to match > the PD at all. Is that correct? [quoted text clipped - 17 lines] > > -MT I'd go to an optician (or your optometrist), and have the PD marked up on the lens along with the pupillary height. Then have them mark the OC on the lens. If your PD has changed a full 5mm in the last 6 years, who's to say how much your facial dimensions have changed. Especially in relation to how your frames sit on your face. You *could* have some vertical displacement as well, which as Mike said, would cause you more problems than the horizontal would. You said that your -3.0D had not changed in 6 years. Is that a statement corraborated by a recent eye exam? The reason I asked, is that you stated a cost concern for new glasses (and a sentimental attachment to your present frames) which makes me question whether a recent exam has been performed. If you have had a recent eye exam and no abnormalities were found and there is no vertical displacement when you have the lenses checked, then I would follow Mike's advice and have a CT if not a full neurological work-up. -=# Firewalker #=- > > the right or left. So eyeglasses OC doesn't have to match > > the PD at all. Is that correct? [quoted text clipped - 38 lines] > > - Show quoted text - There is a vertical displacement but I thought it is insignificant. Anyway. I think I'll just get a new pair of glasses since the original pair design is kid-like as I got it when I was 10 years old. Willy > > > the right or left. So eyeglasses OC doesn't have to match > > > the PD at all. Is that correct? [quoted text clipped - 47 lines] > > - Show quoted text - Getting anew pair of glasses would probably be advisable. So would a new eye exam, if it's been more than a year since your last. If you wear single-vision (and at your age, I would assume you do) then check out that site I gave you. Many of the online optical shops do an excellent job (despite what many opticians will tell you) when it comes to single vision lenses, and the frames are of compareable quality to many namebrands and at unbelievably lower prices. If you needed progressive lenses, *then* I'd tell you to stick with a local optician. Too many variables to contend with in measuring for a set of progressive lenses. -=# Firewalker #=- > vertical displacement when you have the lenses checked, then I would > follow Mike's advice and have a CT if not a full neurological work-up. Sorry I was being funny. I'm pretty sure the OP meant his FRAME OC was 5mm larger, not that his actual HEAD had grown that much. In an adult, that would be pretty alarming. -MT > > vertical displacement when you have the lenses checked, then I would > > follow Mike's advice and have a CT if not a full neurological work-up. [quoted text clipped - 3 lines] > I'm pretty sure the OP meant his FRAME OC was 5mm larger, not that his > actual HEAD had grown that much. But if the Frame OC was dead center 5 years go and now it was 5mm larger. It's the same as the actual Head growing that much, no? I was 10 years old when I got the original spectacles. Now 15 years old. I think it's possible my actual head had grown that much. And 5mm is just little. An infant PD is about maybe 40mm. Adolescent PD is 60-70mm. There is typically 20-30mm increase. So 5mm is just little. Willy > In an adult, that would be pretty alarming. > > -MT In article <c94b8e60-0d7e-46d0-8f6d-d860e3a15abd@v5g2000prm.googlegroups.com>, > I was 10 years old when I got the original spectacles. Now 15 years > old. > I think it's possible my actual head had grown that much. And 5mm > is just little. An infant PD is about maybe 40mm. Adolescent PD is > 60-70mm. > There is typically 20-30mm increase. So 5mm is just little. Let's take a vote here. How many people think "Willy Sylers" is just the newest name for Zetsu, who has had many and varied names in his posting career here? SignatureDan Abel Petaluma, California USA dabel@sonic.net > In article > <c94b8e60-0d7e-46d0-8f6d-d860e3a15...@v5g2000prm.googlegroups.com>, [quoted text clipped - 11 lines] > > -- What? heck no.. i'm not and don't know Zetsu. I'd give you my laptop if I was Zetsu or anyone can prove I was Zetsu. I just have a couple of questions here and that's all. Willy > Dan Abel > Petaluma, California USA > da...@sonic.net > In article > <c94b8e60-0d7e-46d0-8f6d-d860e3a15...@v5g2000prm.googlegroups.com>, [quoted text clipped - 14 lines] > Petaluma, California USA > da...@sonic.net I'm pretty new here myself, so I'll bite....who the heck is Zetsu? > I'm pretty new here myself, so I'll bite....who the heck is Zetsu? If you waste even 30 seconds, you'll find his/her/its latest posts. If you take yet another minute, you'll see his/her/its posting history. My guess? The illegitimate love child of Otis Brown -- sci.med.vision's longest running, most prolific, useless, and harmful troll. Again I apologize, because I misunderstood your age. I did say "in an adult" it would be alarming. Between age 10 and age 15, not so strange. -MT > the right or left. So eyeglasses OC doesn't have to match > the PD at all. Is that correct? [quoted text clipped - 10 lines] > horizontal direction, that's almost negligible. Vertical is another story. > 1.5 prism diopters base-up or base-down would be an instant headache. I bought a glass prism at a store. Looking nearest the apex (located at the right).. I can see images in the left most side of the surrounding. Assuming a minus lens in eyeglasses is composed of two prisms connected at the apex at the center (thinner). If the PD is larger than the OC. You are looking at the outermost prism in the frame going to the base. Do our eyes go inward or outward in this case? I realised that some straining can happen because you have to use constant convergence just to focus at infinity. In the case of OC larger than a PD. Do the eyes go outward straining the extraocular muscles? What's the rule for the eyes going inward (converging) or outward (diverging) in PD longer or shorter than the OC? Which is which? For vertical displacement. Our eyes don't have to use convergence or divergence at infinity. So how can vertical cause more problems when you simply have to shift the eyes upward or downward together without getting the crosseye effect? In practice. Should the OC perfectly match the PD? What's the tolerable allowance allowed in ordering a pair by FDA directive? Willy > > > If my eyes PD now is 70 from 65 five > > > years ago. > > I'd have a CT scan right away. > > -MT > the OC. You are looking at the outermost prism in the frame going > to the base. Do our eyes go inward or outward in this case? The image moves toward the apex of a prism. Base-in prism requires the eyes to diverge. > So how can > vertical cause more problems when > you simply have to > shift the eyes upward or downward > together without getting > the crosseye effect? Put the prism over _one_ eye, to see the effect of vertical displacement. You have lots of reserve ability in the horizontal direction. Little bits of prism don't matter much, horizontally. > In practice. Should the OC perfectly match the PD? What's > the tolerable allowance allowed in ordering a pair by FDA > directive? That's why we have a world wide web. -MT > > the OC. You are looking at the outermost prism in the frame going > > to the base. Do our eyes go inward or outward in this case? > > The image moves toward the apex of a prism. Base-in prism requires the eyes > to diverge. But in the case of my eyes PD longer than my smaller frame and OC. It should produce Base Out. Not Base-In. Specifically: For minus lenses. 1. A PD greater than the OCD produces a base out effect. 2. A PD less than the OCD produces base-in prism My PD is greater than the OCD of my old frame. So it is a Base-Out effect right? About what you said that in base-in effect, the eyes would diverge. Is this when seeing at infinity. This means the eyes are constanly in diverge mode even seeing far. Can this produce the appearance of Exotropia (where the eyes are deviated outward)? For PD greater than OCD, the effect is base-out and convergence. For such patience. If they are seeing at infiniity. Do their eyes get the appearance of Esotropia (both eyes turning inward). Most. Importantly. Can wearing off-center spectacles produce permanent Strabismus like Esotropia or Exotropia by disorienting the extraoccular muscles or neural balance? I was describing the horizonal displacement only in the above. > > So how can > > vertical cause more problems when [quoted text clipped - 4 lines] > > Put the prism over _one_ eye, to see the effect of vertical displacement. Putting it over one eye, the images in the monitor are shifted to the apex. But I can imagine getting a second prism and seeing the same images upward. In the case of vertical displacement with similar say 2mm OC displacement upward, you only have to adjust your eyes together upward or downward. This is less strenous than horizontal displacement in which you have to do all day convergence just seeing an object an infinity. Vertical displacement can only be a problem if one OC is higher than pupil and one OC is lower than pupil. Agree? > You have lots of reserve ability in the horizontal direction. Little bits of > prism don't matter much, horizontally. Even if one has lots of reserve ability in the horizontal. Fatique can still be experienced between perfectly centered OC/PD glasses and off centered combination, isn't it. Also why do you say horizontal direction has more reserve ability. Is it because of the fact that our eyes know how to converge. But in moving the eyes up and down. It has even more reserve ability because of the fact our eyes can move up and down.. except if one has to move left eye upward and right eye downward together.. is this what you mean the vertical has lesser reserve ability because they can't do particular aspect? Willy > > In practice. Should the OC perfectly match the PD? What's > > the tolerable allowance allowed in ordering a pair by FDA [quoted text clipped - 3 lines] > > -MT > But in the case of my eyes PD longer than my smaller frame and OC. > It should produce Base Out. Not Base-In. Specifically: I wasn't trying to flesh out your specific problem, just stating the rule. Since base-in requires divergence, it follows that base-out will require convergence. You got it. > About what you said that in base-in effect, the eyes > would diverge. Is this when seeing at infinity. This means > the eyes are constanly in diverge mode even seeing > far. Can this produce the appearance of Exotropia > (where the eyes are deviated outward)? I'm sure it could _appear_ that way but how you see matters more than how you look. > For PD greater than OCD, the effect is base-out and > convergence. For such patience. If they are seeing > at infiniity. Do their eyes get the appearance of Esotropia > (both eyes turning inward). I'm all twisted around. Once you understand phoria and tropia a little better, it's easier to put your questions in logical form. With base-out prism, you must converge to see single. So yes, someone who peeps around your lenses will see that you are converging. Not apparent, but real convergence. > Most. Importantly. Can wearing off-center spectacles produce > permanent Strabismus like Esotropia or Exotropia by disorienting > the extraoccular muscles or neural balance? Not likely, if you have normal vision before. You can disturb the binocular reflexes and even modify them over time, but normal eyes are pretty durable. >> Put the prism over _one_ eye, to see the effect of vertical displacement. > Putting it over one eye, the images in the monitor are shifted to the > apex. Putting the same vertical prism over both eyes, the two prisms cancel out. There's no effect on your binocular reflexes and it's only useful if you have some condition like a neck brace where you can't bend your head to see your feet and walk. > an infinity. Vertical displacement can only be a problem if one > OC is higher than pupil and one OC is lower than pupil. Agree? That's right. > Even if one has lots of reserve ability in the horizontal. Fatique can > still be experienced between perfectly centered OC/PD glasses and off > centered combination, isn't it. Yes, but if your prescription is +/-3 or so, it isn't necessary to split millimeters. > Also why do you say horizontal > direction has more reserve ability. > Is it because of the fact that our eyes > know how to converge. You'd only need VERTICAL convergence if you had one eye ABOVE the other. Then you'd need no HORIZONTAL vergence. > But in moving the eyes up and down. It has > even more reserve ability because of the fact our eyes can move > up and down.. except if one has to move left eye upward and right > eye downward together.. is this what you mean the vertical has > lesser reserve ability because they can't do particular aspect? Vergence movements are in the horizontal plane because the eyes are in the horizontal plane. You make use of horizontal diplopia and horizontal vergence to define your position and your surroundings. Vertical diplopia isn't normal, isn't tolerated and it doesn't normally change. -MT > > But in the case of my eyes PD longer than my smaller frame and OC. > > It should produce Base Out. Not Base-In. Specifically: [quoted text clipped - 19 lines] > I'm all twisted around. Once you understand phoria and tropia a little > better, it's easier to put your questions in logical form. Phoria = latent deviation Tropia = manifest deviation Without any spectacles. I guess that there is never a case that those with "normal vision" have to deviate the eyes outward to see. So its first time in millions of years wherein spectacles are causing them. I guess contact lens don't have any problems with prismatic effect, isn't it. > With base-out prism, you must converge to see single. So yes, someone who > peeps around your lenses will see that you are converging. Not apparent, but [quoted text clipped - 37 lines] > You'd only need VERTICAL convergence if you had one eye ABOVE the other. > Then you'd need no HORIZONTAL vergence. If the decentered spectacles cause you to raise one eye above another in base-up or base-down situation. You still need horizontal vergence if you are going to read close, isn't it. Or are you saying one of the intraocular muscles or two of them is both causing the vertical and horizontal vergence in the situation above compare to if normal horizontal vergence is used which uses other muscles. I can't find reference of this in the internet. What intraocular muscles are involved in vertical vergence and/or horizontal vergence? > > But in moving the eyes up and down. It has > > even more reserve ability because of the fact our eyes can move [quoted text clipped - 12 lines] > > -MT If one move the spectacle sideways up and down, one can see that at a certain angle, you would experience diplopia (as when one frame is higher up than the other). Do you know of a simple way to know if your eyes are seeing at the optical center of the glasses vertically? Any grid lines or chart that one can use to test this readily or seeing with and without eyeglasses and noticing any deviation of the images? Also if I'd order a new pair. What kind of eyeglasses machine (preferably automatic) must I look for wherein they can accuratelygrind and put the OC at a right distance given the frame dimensions. I don't want the optician to just grind my glasses manually using chisel and then estimate where the OC would be in the frame. This is how they did my old glasses that's why it's a bit off even vertically as tested in the lensometer. In the glasses you saw, is the OC dead center in the frame or is 1-2mm displacement normal? What's the standard based on your actual experience in this matter? Many thanks. Willy > Without any spectacles. I guess that there is never a case that > those with "normal vision" have to deviate the eyes outward False... you must diverge quickly when changing gaze from near-to-far, so "never" isn't the word. We use convergence more, because divergence is normally assisted by the eyes wanting to return to zero, eg straight-ahead gaze, the position-of-rest indicated by the unilateral cover test. The brainstem reflexes that keep your vision single can actively pull your eyes out of convergence, but divergence is also accomplished by relaxation. CONvergence is much easier and more developed. It's so easy it's fun, crossing our eyes to make funny faces. > I guess contact lens don't have any problems with prismatic > effect, isn't it. Good question and good intuition. The closer your lenses are to your eye, the less prismatic effect. Prentiss' rule for induced prism assumes the lenses are at 10mm, the "spectacle plane." > If the decentered spectacles cause you to raise one eye above > another in base-up or base-down situation. You still need horizontal > vergence > if you are going to read close, isn't it. Sure. They're independent. > horizontal vergence is used which uses other muscles. I can't > find reference of this in the internet. What intraocular muscles > are involved in vertical vergence and/or horizontal vergence? The muscles that make your eyes go up and down work conjugately. They remain yoked together vertically, at the same azimuth all the time. > If one move the spectacle sideways up and down > frame is higher up than the other). Do you know of a simple way > to know if your eyes are seeing at the optical center of the > glasses vertically? Yes. If it hurts, get it checked out. If it doesn't hurt and you don't see double vertically, forget about it. You are flogging a dead molehill. > Any grid lines or chart that one can > use to test this readily or seeing with and without eyeglasses > and noticing any deviation of the images? Are your glasses uncomfortable? Do you see double? If so, get them fixed. If not, let's find something else to talk about. > Also if I'd order a new pair. What kind of eyeglasses > machine (preferably automatic) must I look for wherein they > can accuratelygrind and put the OC at a right distance given > the frame dimensions. Bummer. PDs are easy to measure with a mm rule. > This is how they did my > old glasses that's why it's a bit off even vertically as > tested in the lensometer. If the glasses were comfortable, the lensometer doesn't always count. > In the glasses you saw, is the OC dead center in the > frame or is 1-2mm displacement normal? What's the > standard based on your actual experience in this > matter? You cannot figure a "standard" for all powers. In low powers it hardly matters. In high powers it matters a lot. In mixed hi/lo, plus/minus it can be very difficult. I don't like to see more than a mm of _vertical_ displacement. I'd gripe if the horizontal was off more than 3-4 mm but some prescriptions / some people could tolerate 20 mm horiszontally with NO awareness. -MT > > Without any spectacles. I guess that there is never a case that > > those with "normal vision" have to deviate the eyes outward [quoted text clipped - 5 lines] > wanting to return to zero, eg straight-ahead gaze, the position-of-rest > indicated by the unilateral cover test. I'm not talking about diverging where our eyes return to zero or straight ahead gaze or position of rest but one where it is deviated outward to ears. I initially thought base-in and diverging means that each of the eye goes outward like in of Exotropia (where the eyes are deviated outward). But then if the base-in diopters is too much. Won't your eyes have to be deviated outward just to look at the center? This is what I meant lens could cause the situation that doesn't happen naturally in millions of years. As another illustration. Supposed you are looking straight ahead or at infinity or have a base-in lens making your eyes diverse outward. What prism diopters would cause your eyes to deviate the maximum such that people looking at you could see your eye black part nearest the side of the eyelids going to the ears? Or are you saying that the maximum deviations base-in prismatic errors can do is to put it back to zero or straight ahead and not deviate further more to the sides to the ears (like our extraocular muscles can't be made to work to make the eyes deviate to the ear sides at will via the base-in lens but this only occuring due to disfunctional muscles/neurons causing Exotropia)? > The brainstem reflexes that keep your vision single can actively pull your > eyes out of convergence, but divergence is also accomplished by relaxation. [quoted text clipped - 23 lines] > The muscles that make your eyes go up and down work conjugately. They remain > yoked together vertically, at the same azimuth all the time. Superior and Inferior Rectus Extraocular muscles rotate eyes up and down conjugately. Now if the say right side of the eyeglasses have base-up diopter prismatic effect. How do the extraocular muscles cause say the right eye to go down while the left eye remain at center or the left eye is at center while the right eye would be downward near the lid? Noting the Superior and Inferior Rectus Extraocular muscles are innerved by Cranial Nerve III so they should control them simultaneously but base-up or base-down prismatic effect can change the synchronization. > > If one move the spectacle sideways up and down > > frame is higher up than the other). Do you know of a simple way [quoted text clipped - 3 lines] > Yes. If it hurts, get it checked out. If it doesn't hurt and you don't see > double vertically, forget about it. You are flogging a dead molehill. Did you forget. I won't see double even if there might be potential to see double because the eyes can adjust independent by extraocular muscles tension in cases of vertical displacement. So seeing double is not the sign of decentered glasses because the eyes can readjust each muscle at the cost of extraocular muscular fatique and tension. Willy > > Any grid lines or chart that one can > > use to test this readily or seeing with and without eyeglasses [quoted text clipped - 31 lines] > > -MT > to be deviated outward just to look at the center? > This is what I meant > lens could cause the situation that doesn't > happen naturally in millions > of years. Sure. Then what? It's a little uncomfortable. A lot of it is very uncomfortable. More than that and things go double because you can't compensate anymore. Nothing gets broken and the laws of physics aren't violated. > As another illustration. Supposed you are looking straight ahead > or at infinity or have a base-in lens making your eyes diverse > outward. What prism diopters would cause your eyes to > deviate the maximum such that people looking at > you could see your eye black part nearest the side of the > eyelids going to the ears? Prism diopter units only work for small angles - a few degrees or fractions of degrees. You're talking about big angles like 45 degrees and the question is silly for several reasons. -nobody does it except as a lark. -big prisms deviate light in other ways that create distortions and make things unrecognizeable. -again you're only concerned about how it would _look_, nothing to do with vision. > Or are you saying that the maximum deviations base-in > prismatic errors can do is to put it back to zero or straight [quoted text clipped - 3 lines] > base-in lens but this only occuring due to disfunctional > muscles/neurons causing Exotropia)? You've lost me. You need to actually work with some prisms and answer some of these questions for yourself. -MT > The brainstem reflexes that keep your vision single can actively pull your > eyes out of convergence, but divergence is also accomplished by [quoted text clipped - 26 lines] > remain > yoked together vertically, at the same azimuth all the time. Superior and Inferior Rectus Extraocular muscles rotate eyes up and down conjugately. Now if the say right side of the eyeglasses have base-up diopter prismatic effect. How do the extraocular muscles cause say the right eye to go down while the left eye remain at center or the left eye is at center while the right eye would be downward near the lid? Noting the Superior and Inferior Rectus Extraocular muscles are innerved by Cranial Nerve III so they should control them simultaneously but base-up or base-down prismatic effect can change the synchronization. > > If one move the spectacle sideways up and down > > frame is higher up than the other). Do you know of a simple way [quoted text clipped - 3 lines] > Yes. If it hurts, get it checked out. If it doesn't hurt and you don't see > double vertically, forget about it. You are flogging a dead molehill. Did you forget. I won't see double even if there might be potential to see double because the eyes can adjust independent by extraocular muscles tension in cases of vertical displacement. So seeing double is not the sign of decentered glasses because the eyes can readjust each muscle at the cost of extraocular muscular fatique and tension. Willy > > Any grid lines or chart that one can > > use to test this readily or seeing with and without eyeglasses [quoted text clipped - 34 lines] > > -MT > Hi, > > I have grown up since I first wore glasses 6 years ago. I still > have the same -3.0 eyes. I heard that if the PD of the eyes > don't match the OC (as my PD got wider), there would be > prismatic effect. What is prismatic effect? > Superior and Inferior Rectus Extraocular muscles rotate eyes up > and down conjugately. Now if the say right side of the eyeglasses [quoted text clipped - 6 lines] > but base-up or base-down prismatic effect can change > the synchronization. Me thinks Dan Abel was correct in his assumtion of this individual. Judging from the first post above to the last post, this person has picked up *quite* a education in less than a week. Doesn't it seem strange how "he" can go from ignorance of prismatic effects, to highly technical statements about the cranial nerves stimulating the extraocular muscle groups in six days? I've heard of prodigies, but this seems a bit hard to swallow. -=# Firewalker #=- In article <00aefd13-e11e-433d-abe1-bc06251ae31d@o36g2000yqh.googlegroups.com>, > > prismatic effect. What is prismatic effect? > > > Superior and Inferior Rectus Extraocular muscles rotate eyes up > > and down conjugately. Now if the say right side of the eyeglasses > > have base-up diopter prismatic effect. > Me thinks Dan Abel was correct in his assumtion of this individual. > [quoted text clipped - 4 lines] > stimulating the extraocular muscle groups in six days? > I've heard of prodigies, but this seems a bit hard to swallow. I think Willy is due for my killfile pretty soon. I've seen this before, many times. It takes very little time to learn some words, assuming that the person doesn't understand what they mean. I suspect that Willy doesn't know what those words mean. I think if Mike posted about the effect of disestablishmentarianism on prism, that within two days, Willy would be using disestablishmentarianism and prism in the same sentence. Just that one post that Willy recently made, about how our eyes have never naturally diverged and converged for millions of years was enough. When we read a book, our eyes converge on the print. When we then look up at infinity, our eyes diverge to point straight ahead. I know so little about prism as it affects eyesight as to be pathetic. Reading Willy's posts about prism will just fill my brain with useless and bad information. SignatureDan Abel Petaluma, California USA dabel@sonic.net > In article > <00aefd13-e11e-433d-abe1-bc06251ae...@o36g2000yqh.googlegroups.com>, [quoted text clipped - 33 lines] > > - Show quoted text - Our eyes extraocular muscles have capability to move the eyes horizontally, vertically and convergence when seeing close. But there is no natural capability to move the eyes sideways to the temple or ears (opposite of cross eye). This is what I meant that in millions of years we can't do this kind of divergence from parallel to the temple or ear side. But base-in prismatic effect of glasses change all that because it can flex your extraocular muscles to move the eyes to the temple or ear side when supposedly looking straight ahead with the base-in glasses. Get this? This is what I meant. I'm interesting in this because my glasses not only have vertical displacement of 2mm but also horizontal displacement. Since I have only one shot for the next glasses to be right as I don't want to spend a lot of money for it. I want to be sure the OC would be dead center with the PD. Willy > > Hi, > [quoted text clipped - 24 lines] > > -=# Firewalker #=- Well. I'm a video gamer and in the world of video games. One can even learn nuclear physics and even many details on particle beam weapon so we gamers are highly technical people and it is even easier to learn thanks to the internet. I asked a lot because I found out my eyeglasses have vertical displacement of 2mm. So I was wondering how to have it fixed whether to look for optician who can fabricate glasses while you wait an hour or one who lets you wait for 5 hours as I wonder what equipment they have that can produce more accuracy in fully centering the lens to produce dead on PD/OC. Willy > > > Hi, > [quoted text clipped - 43 lines] > > - Show quoted text - Also I have previously used a binocular when treking. At first, I got headache looking at it. Then I found out from newsgroup that the images in the left and right don't converge. That is. Many binoculars are not fully centered giving you headaches. A few days ago. I realised that prismatic effect could be related to it. I initially thought prismatic effect only distort colors. Then I buy a prism to see near the apex and realised images could really shift. Then after hours of internet reading. Found out what Base-in and Base-out mean. But still have questions the answers of which I can't find like whether how much the eyes can both diverge to the temple from parallel straight thru. It is my guess that the vertical displacement intolerance of the eyes has same degree to the displacement from parallel to the temple since our eyes are not designed that way? This means we can tolerate more base-out error than base-in because the former we can adjust but the latter can't? About teenagers having sharp brain. It's true. Our mitochondria are still prime (yes I remember my biology lessons). We don't produce much free radicals. We are at the prime of life and optimum health. When a person gets beyond 20 year old. The skin gets older because there are more free radicals which can also affect the brain neurons. This is also why it can take me just hours to learn about prismatic effect which can take you months to learn. So my increasing knowledge of it in just days is not surprising. We memorize and analyze a whole lot more in schools. Willy In article <1b74fd59-a82f-4c6a-9724-dbc9e09f4625@f1g2000prb.googlegroups.com>, > About teenagers having sharp brain. It's > true. Our mitochondria are still prime (yes [quoted text clipped - 11 lines] > days is not surprising. We memorize and > analyze a whole lot more in schools. When I was a boy of fourteen, my father was so ignorant I could hardly stand to have the old man around. But when I got to be twenty-one, I was astonished at how much the old man had learned in seven years. Mark Twain I'm 59 years old now. Definitely over the hill. SignatureDan Abel Petaluma, California USA dabel@sonic.net > In article > <1b74fd59-a82f-4c6a-9724-dbc9e09f4...@f1g2000prb.googlegroups.com>, [quoted text clipped - 26 lines] > Petaluma, California USA > da...@sonic.net There is a saying "use it or lose it". We teenagers use our brain so much having to study 8 hours a day memorizing stuff, doing arithmetic, etc. and our neurons keep growing. For people older who don't use their brain. The neurons regenerate until they got the brains of 8 year old. If you are active and use your brain even past 50. You can still beat a teenager but with more effort. This is why Nobel Prizes are won mostly below 30 years old. BTW.. I just ordered the book "Spectacles Lenses: Theory and Practice by Colin Fowler BSc PhD FSMC FCOptom and Keziah Latham Petre PhD BSc MCOptom. It may be expensive but at least I'd get my next glasses right by watching over the fabrication process. The book would give me the knowledge to avoid incompetent opticians who create vertical displacement of more than 1mm. Willy Willy Hi Willy, If your main problem is the Rainbow effect, the could be caused by the ABBE Factor of the lens. ABBE Factor is a measuring unit of Chromatic Aberration (This is the way a substance can break the light into different colors of the spectrum) of the lens material, the Higher the number the less chromatic aberration you'll have. Even though Policarbonate lenses provide a lot of comfort because they are so light and very strong (Usually recommended for Safety Protection), it is one of the lenses with less ABBE factor number. You might want to go back to regular Plastic lenses or there is a similar lens call Trivex that has one of the highest ABBE Facto. >Hi, > [quoted text clipped - 10 lines] > >Willy Sylers |
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