Results 1 to 22 of 22

Thread: IOT Aspheric single vision

  1. #1
    OptiBoardaholic
    Join Date
    Jun 2006
    Location
    Panama
    Occupation
    Optometrist
    Posts
    235

    IOT Aspheric single vision

    Recently the Freeform IOT software was instaled in our Innovations server.
    Could someone help me understand why a prescription of -8.00 sph. single vision once calculated with Innovations and IOT software, it became -7.64 -0.27 x 62°? This is a IOT aspheric lens calculation.

    Thanks in advanced.

  2. #2
    OptiWizard
    Join Date
    Apr 2014
    Location
    California
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    382
    looks like it's compensating for wrap, panto, and vertex distance.

    if you set panto and wrap to 0 and vert to 13, you should get -8.00sph(aspheric back curve though)
    Last edited by ml43; 04-22-2015 at 11:44 PM.

  3. #3
    OptiBoardaholic
    Join Date
    Jun 2006
    Location
    Panama
    Occupation
    Optometrist
    Posts
    235
    That is what i thought.
    Just checked. Default values on Innovations are Panto 9.50 Tilt 5.00 Vertex Distance 13.
    Looks like this defaults are for all jobs where panto tilt and vertex distance are not specified and no matter which is the prescription.
    This is a -8.00 with front curve less than 1.00D. on a regular plastic frame.
    The values you just gave are closer to the characteristics of the frame on this job.
    I will vote for variable defaults based on prescription and base curve.

    Thanks for your advice

  4. #4
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
    Join Date
    May 2000
    Location
    Seaford, NY USA
    Occupation
    Dispensing Optician
    Posts
    6,008
    A Panto of 9.5 degrees for todays tall frames is NOT common in my experience.

    B

  5. #5
    One eye sees, the other feels OptiBoard Silver Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    5,458
    Quote Originally Posted by Barry Santini View Post
    A Panto of 9.5 degrees for todays tall frames is NOT common in my experience.

    B
    Same here. I'm convinced that the manufacturers don't build in sufficient panto because the frame bottom might touch the cheek "off the rack", before pre-adjusting, decreasing sales.

    I would use a five degree default for both the wrap and panto tilt, but the optician should be measuring all of the POW values, especially on an eight diopter lens power.
    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.



  6. #6
    Master OptiBoarder OptiBoard Gold Supporter
    Join Date
    Mar 2012
    Location
    Maryland
    Occupation
    Dispensing Optician
    Posts
    2,103
    What if the prescribing doctor doesn't just copy what had the patient seeing 20/20 in their manifest refraction into the RX. What if they alter the RX?

    I often wonder if in these situations patients are worse off with POW compensation. Say that the patient was seeing 20/20 at -8.25 in the exam lane, but the RX reads -8.00, would the compensation bringing that to -7.64 -0.27 x 62° be more problematic?

  7. #7
    OptiWizard
    Join Date
    Apr 2014
    Location
    California
    Occupation
    Other Optical Manufacturer or Vendor
    Posts
    382
    Quote Originally Posted by Tallboy View Post
    What if the prescribing doctor doesn't just copy what had the patient seeing 20/20 in their manifest refraction into the RX. What if they alter the RX?

    I often wonder if in these situations patients are worse off with POW compensation. Say that the patient was seeing 20/20 at -8.25 in the exam lane, but the RX reads -8.00, would the compensation bringing that to -7.64 -0.27 x 62° be more problematic?
    POW compensation can be problematic if the measurements aren't accurate. But if you know your measurements are within tolerance, then most of the time, the POW compensation will decrease the peripheral distortion while maintaining VA.

    You can always just choose a digital design that doesn't have POW compensation.
    Almost all lens manufacturers/designers have equivalent designs without compensation.
    Or just specify to the lab what parameters you would like to be set.
    Should only take them an extra minute or so.

  8. #8
    Master OptiBoarder OptiBoard Gold Supporter
    Join Date
    Mar 2012
    Location
    Maryland
    Occupation
    Dispensing Optician
    Posts
    2,103
    My measurements are usually/always accurate, and I often use non compensated digital designs. What I am referring to is doctors who refract "soft" and I have no idea they do, so since a patient is already a little under minused ( say to stave off negative effects of early presbyopia) when such an RX is compensated, with correct measurements, problems abound!

  9. #9
    One eye sees, the other feels OptiBoard Silver Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    5,458
    Quote Originally Posted by Tallboy View Post
    My measurements are usually/always accurate, and I often use non compensated digital designs. What I am referring to is doctors who refract "soft" and I have no idea they do, so since a patient is already a little under minused ( say to stave off negative effects of early presbyopia) when such an RX is compensated, with correct measurements, problems abound!
    The lens is compensated because tilting the lens changes the Rx. It's bad if the Rx is fudged, but compensating doesn't make it worse. Not compensating will make it worse though, especially for this Rx power.

    If you're not manufacturing with advanced software on a FF platform, then a good workaround to minimizing power and astigmatism on-axis errors, due to pantoscopic tilt, is to align the optical axis of the lens with the center of rotation of the eyes, that is, inferiorly decentering the optical center .5mm per one degree of pantoscopic tilt. Wrap tilt should be kept to a minimum because it would require a negative value for the wrap angle. BO prism is also induced from wrap, but is ignored due to the low values (usually about .13∆), and considering our substantial horizontal fusional reserves.

    However, SVFF is usually better, with the right software, if there is sufficient power, because we can place the OC level with the primary gaze, minimizing chromatic aberration without degrading the on-axis optics, even when there are high values of tilt. Moreover, oblique astigmatism and power error is minimized across a fairly wide range of BCs, significantly improving the peripheral optics when there are unusual BC requirements (sunglasses) and/or high tilt values.
    Last edited by Robert Martellaro; 04-28-2015 at 10:03 AM. Reason: typo/brain freeze...direction of induced prism from tilt.
    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.



  10. #10
    Master OptiBoarder OptiBoard Gold Supporter
    Join Date
    Mar 2012
    Location
    Maryland
    Occupation
    Dispensing Optician
    Posts
    2,103
    Remember the study Sharpstick777 said he did at his lab? Where they surveyed people between which lenses they liked better, Seiko front radially Aspheric designs or FF POW compensated? Wasn't his results that up until about -7.00 they mostly preferred the molded semifinished designs from stock over the custom FF? It was after stronger than that in the sphere, or with considerable cylinder powers that those surveyed found the FF lenses to be better.

    I think about this all the time, about the difference between theoretical math of optics and what actually works on someones face (not to mention keeps my business viable!) There is obviously a HUGE incentive for labs to say that their more expensive surfaced designs are better.

    I'm not sure I know anything, I just wanted to bring up those points. Also I wonder if Dr.s all don't fully refract to 20/20, or rather try and keep "as much plus" as possible while still delivering satisfactory vision in distance.

  11. #11
    One eye sees, the other feels OptiBoard Silver Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    5,458
    Quote Originally Posted by Tallboy View Post
    Remember the study Sharpstick777 said he did at his lab? Where they surveyed people between which lenses they liked better, Seiko front radially Aspheric designs or FF POW compensated? Wasn't his results that up until about -7.00 they mostly preferred the molded semifinished designs from stock over the custom FF? It was after stronger than that in the sphere, or with considerable cylinder powers that those surveyed found the FF lenses to be better.
    When fit optimally, front or back aspheric lenses will offer similar performance in minus spherical powers.

    I think about this all the time, about the difference between theoretical math of optics and what actually works on someones face (not to mention keeps my business viable!) There is obviously a HUGE incentive for labs to say that their more expensive surfaced designs are better.
    It's our job to know when aberrations are likely to be seen by the eyeglass wearer sitting across from us at the dispensing table. Sometimes it's a tough call, other times it's clear cut. Know the science, then know your client.

    I'm not sure I know anything, I just wanted to bring up those points. Also I wonder if Dr.s all don't fully refract to 20/20, or rather try and keep "as much plus" as possible while still delivering satisfactory vision in distance.
    There are times when they might overplus slightly, maybe for an elderly person who's world is strictly indoors with no driving, but most everyone else gets the BCVA at infinity. For younger healthy eyes, that's about 20/15 or better.

    http://journals.lww.com/optvissci/Ab...hood_in.6.aspx
    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.



  12. #12
    Master OptiBoarder OptiBoard Gold Supporter
    Join Date
    Mar 2012
    Location
    Maryland
    Occupation
    Dispensing Optician
    Posts
    2,103
    Thank you Robert, as always you clarify things for me.

  13. #13
    OptiBoardaholic
    Join Date
    Jun 2006
    Location
    Panama
    Occupation
    Optometrist
    Posts
    235
    Thanks to all for your opinions.
    Lets see if I understood!
    On this case we used IOT aspheric single vision. So the lens would be aspheric even no panto or wrap is used.
    Panto, wrap and vertex distance has influence on the efective power of the lens and that is why the lens is compensated.
    The compensation is more important on higher prescription. .
    This default value are true if the frame is properly choosen and the prescription is the correct too. (No soft refract).

    What will I do.
    Ask for real value of panto and wrap on every prescription that is to be compensated. Avoid defalt value. This is guessing.
    If no real value are supplied, i might no apply compensation.
    On low prescritions the compensation is soo small that it doe not matter if used or not.
    Any way, If patient is not confortable with a new prescription, the responsable will be the compensation no matters if the cause is another.
    Other optometrist of the group has to be well informed of all of this and how to handle this cases.
    Will keep on the patient record the refracted prescription and the compensated one for each pair of lenses the patient buy. Fortunately it is small the percentge where the compensation make important changes on the prescription.

  14. #14
    What's up? drk's Avatar
    Join Date
    Mar 2004
    Location
    Ohio
    Occupation
    Optometrist
    Posts
    9,386
    Quote Originally Posted by Robert Martellaro View Post
    There are times when they might overplus slightly, maybe for an elderly person who's world is strictly indoors with no driving, but most everyone else gets the BCVA at infinity. For younger healthy eyes, that's about 20/15 or better.

    http://journals.lww.com/optvissci/Ab...hood_in.6.aspx
    Agree. I don't think many ODs do other than max out the distance vision.

  15. #15
    What's up? drk's Avatar
    Join Date
    Mar 2004
    Location
    Ohio
    Occupation
    Optometrist
    Posts
    9,386
    Quote Originally Posted by Robert Martellaro View Post
    Wrap tilt should be kept to a minimum because it would require a negative value for the wrap angle.
    Can you clarify what you mean by this, please?

    BI prism is also induced from wrap, but is ignored due to the low values (usually about .13∆), and considering our substantial horizontal fusional reserves.
    BO induced, BI ground to compensate, right?

    However, SVFF is usually better, with the right software, if there is sufficient power, because we can place the OC level with the primary gaze, minimizing chromatic aberration without degrading the on-axis optics, even when there are high values of tilt. Moreover, oblique astigmatism and power error is minimized across a fairly wide range of BCs, significantly improving the peripheral optics when there are unusual BC requirements (sunglasses) and/or high tilt values.
    This is new to me. So you're saying that specifying a level MRP 1 mm lower than pupil center per 2 degrees of panto induces things like vertical disparity in unequal power lenses and chromatic aberration. Got that part.

    But when free form single vision lenses are used, the ideal nature of the aspheric/atoric curves make obsolete the need to move the lenses' optical axis to intersect the eyes (theoretical) center of rotation? This I don't get.

    I have assumed that the optical axis intersects the center of rotation for some benefit when the eye looks down. What is the purpose?

  16. #16
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
    Join Date
    May 2000
    Location
    Seaford, NY USA
    Occupation
    Dispensing Optician
    Posts
    6,008
    Quote Originally Posted by drk View Post
    Agree. I don't think many ODs do other than max out the distance vision.
    This (default) premise..."maxing out the distance vision"...is flawed, IMHO.

    B

  17. #17
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
    Join Date
    May 2000
    Location
    Seaford, NY USA
    Occupation
    Dispensing Optician
    Posts
    6,008
    Really...seriously, we must understand that "actual" POW values are still approximates by their very nature.

    No one agrees on what constitutes "correct" pantoscopic angle, since it correlates with posture and pantoscopic tilt.

    No one agrees on precise wrap angle, unless the base curve of the lens EXACTLY matches the bevel curve of the frame, and that the lenses are positioned within the frame as if they were planos...i.e., the bevel apex is placed 1mm from the front surface.

    Don't get hung up on the numbers. Who's making the lenses, and the material choice, is equally important.

    B

  18. #18
    What's up? drk's Avatar
    Join Date
    Mar 2004
    Location
    Ohio
    Occupation
    Optometrist
    Posts
    9,386
    Quote Originally Posted by Barry Santini View Post
    This (default) premise..."maxing out the distance vision"...is flawed, IMHO.

    B
    What would you recommend?

  19. #19
    One eye sees, the other feels OptiBoard Silver Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    5,458
    Quote Originally Posted by drk View Post
    Can you clarify what you mean by this, please?
    If we decenter the lens in, aligning the optical axis with the eye's center of rotation, we would need to introduce negative facial wrap (unwrap!), one degree for every .5mm of decentation. Same as when we tilt around the horizontal meridian.

    BO induced, BI ground to compensate, right?
    Yes. Good catch!

    This is new to me. So you're saying that specifying a level MRP 1 mm lower than pupil center per 2 degrees of panto induces things like vertical disparity in unequal power lenses and chromatic aberration. Got that part.
    Right.

    But when free form single vision lenses are used, the ideal nature of the aspheric/atoric curves make obsolete the need to move the lenses' optical axis to intersect the eyes (theoretical) center of rotation? This I don't get.
    Because the software compensates. Not all SVFF designs can do this though.

    I have assumed that the optical axis intersects the center of rotation for some benefit when the eye looks down. What is the purpose?
    The benefit is decreased power and astigmatism (error) at all angles of gaze, for all lens designs, although as noted above, there is more latitude with some FF softwares. (primarily a concern with aspheric/atoric surface designs and/or very high dioptric values)
    Last edited by Robert Martellaro; 04-28-2015 at 12:58 PM.
    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.



  20. #20
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
    Join Date
    May 2000
    Location
    Seaford, NY USA
    Occupation
    Dispensing Optician
    Posts
    6,008
    Quote Originally Posted by drk View Post
    What would you recommend?
    More robust information about what the RX represents. I agree with Robert M: Mature presbies don't like their plus cut back indoors, but suns...that's another thing entirely.

    Current Rx paradigm is way too simplistic for an educated fulfiller to make the proper eyewear for the client's needs.

    B

  21. #21
    What's up? drk's Avatar
    Join Date
    Mar 2004
    Location
    Ohio
    Occupation
    Optometrist
    Posts
    9,386
    I think the most information-rich way is for the prescriber to default to full distance Rx, and then adds can be designed to suit their needs.

    I don't think overminusing a 1/4 D in the suns or night glasses or whatever falls far enough outside ANSI tolerances that you couldn't push that through, if you wanted. But other than that, fudging distance Rx is not very useful.

    Saying all that, why isn't the "straight dope" on the distance Rx sufficient? If there's any special use for the Rx, the prescriber should have written it on there (such as "night glasses", "shooting glasses", etc.).

  22. #22
    Master OptiBoarder MakeOptics's Avatar
    Join Date
    Aug 2011
    Location
    none
    Occupation
    Other Eyecare-Related Field
    Posts
    1,327
    The prescriptions default measures are vd=13 panto=0 and face=0, the measures in your system are the fitted measures ultimately its best to use exp provided measurements but if now supplied then a good guestimate can be calced base off frame demension and patient measures.

    A=52
    B=35
    Dbl=18

    The patient SV:
    PD=32/32

    I don't suggest playing with the VD unless specified but that can be called as well with some assumptions.

    Frame PD = 70 (35/35)
    Decentration (h) = 70 - 64 = 6mm
    Face = 6/2 (1° for every 2mm) 3°
    OC = 2/3 of B or 4 + 1/2 * B (whichever is smaller)
    Panto = (OC - 1/2 * B)/2
    OC = 24 or 22 <= 22 is lower
    Panto = (22 - 18)/2 = 2°

    That's the lens tilt, the frame tilts I use for a good approximation are:
    Face = 5°
    Panto = 8°

    Total tilt is the sum of these values:
    Face = 5 + 3 = 8°
    Panto = 8 + 2 = 10°

    These values are approximations and lens tilt will be calced from IOTs software so really the defaults for frames need to be supplied but I needed an exercise. If vertex distance is supplied then a more accurate tilt can be determined for the lens tilt in IOTs software as 1° for every 2mm is just an approximation for tilt using a schematic eye for the COR to BV. The center of rotation is a combination of approximately 1/2 the axial length of the eye + the vertex distance. The center of rotation can be more accurately described as well given corneal radius and corneal diameter. As we move into a more computer based world the complexity will shift from the lab/optician side to the architect/software designer so its important to document these nuances for a future generation to understand the inner workings however in reality this is an exercise that would be irrelevant on a job to job bases.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Replies: 2
    Last Post: 05-20-2013, 01:39 PM
  2. distortion in vision in upper part of single vision essilor crizal lense
    By vineet7182 in forum General Optics and Eyecare Discussion Forum
    Replies: 7
    Last Post: 04-18-2013, 08:07 AM
  3. Replies: 9
    Last Post: 02-02-2010, 11:22 PM
  4. Replies: 0
    Last Post: 01-17-2003, 10:03 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •