Need copy of ANSI standards for PD's

[Kinnick]

Our office has an ancient and unreadable copy of PD tolerances, like how much they can be off be fore they start inducing prism.

We need a new copy badly. I have looked it up on ANSI.org and they give an abstract description of the article but I can not view it first before I buy it to see if it is exactly what I am looking for.

Can anyone give me any help here? I would be glad to buy it if it met my needs.

Thank you,

Wendi Hurst

[eyevay]

as far as I know, ANSI p.d. tolerances are plus or minus 2.5 mm for both distance & near. I believe horizontal prism tolerance is 2/3 prism diopter & vertical tolerance is 1/3 prism diopter--but I have also heard that it has been changed to 1/2 prism diopter.

If anyone has more definitive info, please correct me.

[Steve Machol]

Please note that the ANSI standards are copyrighted documents. I would advise every office to order their own copy:

ANSI Z80.1-1999

[Joann Raytar]

I believe OLA member labs can provide you with the ANSI Standards if you don't want to order online. If you use one, I would give them a call.

[harry a saake]

:D Kinnick, bear in mind that ANSI is only standards and not the law, you can set your own standards simply by making your own standards higher.
.....Another point is that an ANSI standard or any other standard may mean nothing until all other facets of the fitting are done right, more so in your high powered lenses.
.....As an example if you have a high powered lens and you have not taken into account the refracting vertex distance, versus the fitting vertex distance, and used a distometer to compensate for the difference, all the standards may mean nothing. The lens might be off .50 diopters when you nuetralize it with the focimeter, but that might just be what you need.
.....In short i would set my own standards, which i think with a little bit of math and common sense you can do quite well.

[wmcdonald]

ANSI Standards are based not on the PD, but on the prism value. For example, you can be off 3 miles on a Pl- 0.75x180 and induce no un-wanted hotizontal prism (the power @ 180 is plano). But if you had a -6.00-0.75x180... you see the difference? Follow Steve's link above. You can download a copy...I think it costs about $10.00 or so, but every office must have an ANSI standard. As Harry said, you can make your standards higher if you wish, but they are good rules to go by. Regarding them not being law... that is correct, but meeting those standards will be viewed more favorably in a court of law! They are set by industry experts and not just off the top of their heads.

[eyevay]

wmcdonald,

yep, your points are right on the mark...or should I say, the fitting cross? ...all it takes is a brain...

however, the downloadable ANSI document is $48, not $10.
Big difference for a between-jobs optician.

eyevay

[shanbaum]

wmcdonald said:
ANSI Standards are based not on the PD, but on the prism value.

Yes and no. For mounted lenses, up to certain specified powers (which vary from 2.75D to 3.37D depending on lens type and orientation, i.e., lateral or vertical), the tolerance is specified in prism diopters; over those powers, the tolerance is specified in millimeters.

For unmounted lenses, both dioptric (0.33D) and cartesian (1.0mm) tolerances are specified; I'm certain that the intent of the authors was that the cartesian tolerance applies when the dioptric tolerance is exceeded.

[Jim G]

Think it was also practical. At higher powers, immeasurable lens (mis)placements would result in prism powers out of standards.

[harry a saake]

:D Let me add that by setting your standards higher, i did mean higher then what is acceptable as ANSI standards.
.....As to Warrens comment on plano - 100 x 180, while what he said is correct, as long as there is no prism . It is typical to see these prescriptions with a .25 to .50 prism in the plano meridian and also typical to hear from the lab well theres no power so the prism dont make no difference.
.....Nothing could be further from the truth and if you want to experience what prism does, have your doctor sit you at the phoropter with a plano lens and then start inducing prism.

[wmcdonald]

Hi Robert,
My comments were that ANSI is BASED on prism values. I was making the point that prism is the general reason for PD measurement in the first place. ANSI changes every 5? years or so and I was attempting, although poorly, to describe why we have those tolerances. I haven't bought one in years and did't realize the cost had gone up so high, but as an Optician, if you don't have one you may be in trouble. I appreciate your adding the specific points and they are absolutely correct. I appreciate you addendum to my post.

Best wishes,
Warren

[Darryl Meister]

I would take this discussion a step further and assert that the ANSI Z80.1 Standard is primarily a manufacturing standard (particularly for high powers) and secondarily a visual performance standard (particularly for low powers). This is not to say that the folks at ANSI are more concerned with manufacturing, but only to point out that reasonable expectations of product quality are often constrained by the capabilities of the manufacturing process.

For instance, consider the 1/3 diopter or 1 mm tolerance on prism. For low powers, the 1/3 prism diopter tolerance is based upon several factors related to vision and refraction, including the precision of lens measuring devices like vertometers, the increments of refracting devices like trial lenses/prisms, and the physiological limits of vision for the eye -- such as the "just noticeable difference" of the eye. Essentially, for any power, a minimum centration error of at least 1 mm is allowed during manufacturing. For low powers, this means that the centration or PD can be off by quite a bit before exceeding the "visual" tolerance of 1/3 prism diopter. However, a seemingly infinite amount of prism is acceptable in high powers, if the centration is still off by no more than 1 mm. This is because a certain amount of manufacturing variance is expected and often unavoidable -- at least without driving the cost of eyewear up to a prohibitive amount.

Also, to Harry's point earlier, while the ANSI Standard is not a legal requirement in most cases (except where mandated by licensing boards or by OSHA for the Z87 Standard), it is considered the "standard of practice" or "standard of care" in the United States. Consequently, Federal authorities and those spiffy reporters doing exposes on quality in the Optical Industry will want you to have a good reason for dispensing eyewear that isn't compliant with ANSI Standards.

Best regards,
Darryl
(Representative to ANSI)