Just curious if there is a historical reason for this that revolves around limits of grinding equipment/technology, or is it just that a range of .25 diopters around the "true" prescription is not discernable from an acuity standpoint?
Just curious if there is a historical reason for this that revolves around limits of grinding equipment/technology, or is it just that a range of .25 diopters around the "true" prescription is not discernable from an acuity standpoint?
The equipment and tests are usually in 0.25 steps.Originally Posted by johnsjolly
Generally, a 0.12D step produces no discernable change in acuity as well, which is the reason the equipment is designed this way. However, the occasional person CAN notice the difference and some doctors will prescribe in this manner. Optical tolerances, though, allow 0.12D variation on just about any power so the point may be moot.
Doctors have gotten too lazy and too proud of thier time to check down to .12 steeps. Opticians seem to have forgotten what they are. Labs are unwilling to keep more stock and more tools for grinding.
That's why. Appearently refractionist are no longer smart enough to refract over rigid contact lenses, they just pull the out contacts and refract knowing the Rx will be good only for a few hours afterwhich the cornea will change enough to obviate vision with the Rx. The extra step of refracting over the contacts would at least ensure an accurate basis for the replacement contacts as well as eliminating guesswork as to vertex, etc.
It's a fast food world what can I say.
Chip:cheers:
Is this observation based upon a personal experience in refracting? And are you willing to redo spectacles or contacts if they are 0.12 off?
I have seen many Rxs from a local office that sends out prescriptions in 12ths if the patient asks for their Rx. If the patient buys their glasses in house they order in .25 steps from their lab.
If I filled the Rx and the pt had a problem our Dr. would do a quick refraction to figure out the problem. It was never a .12th difference problem. Axis, severe over\under prescribed, material, etc... was the prolem and it was fixed.
If the patient went back to that Dr.s office with the pair I made they would point out that it was made in quarter steps and not .12th like they prescribed. They put the patient in the chair do a quick check and sell them a pair that is "correct". This is after they make appropriate changes.
In some rare choices 12ths could come into play and if it was necessary any lab should fill the Rx appropriately and the Dr. should would be charged accordingly.
Other than that I personally describe the difference between .12 and .25 as an eleven mile an hour wind and a twelve mile an hour wind. You will not notice the difference.
Thanks labfly. Just a reminder that 0.12D should be pronounced as an "eighth of a diopter" and not "twelfths".
Sad to say but I have reverted back to calling it twelfths myself, because everytime I say eigths I have to explain to someone how it truly is an eigth of a diopter and not a twelfth. :hammer: However if the goal is to teach someone then eigths is the correct fraction of a diopter that should be refered to. I wonder if this terminology will change over time?
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Observation of changes in the last 45+ years.
Now days the O.D.'s are too busy "practicing medicine."
Now days the M.D.'s are too busy doing surgery, managing optical shops and investments to be bothered with refraction.
Hell, I'm so old that I can remember when M.D.'s did surgery on Wednesday morning and if they finished early played golf that afternoon. They all worked a half day on Saturday. The started examinations at 8:30 A.M., took only one hour for lunch and worked 'til 5:00 or 5:30. Now they leave at noon Friday and start work days at 9:00 or later, finish at 3:30.
Say it ain't so Joe ....
Chip,
I'm really glad I don't live anywhere near you. It really seems the worst MDs and ODs congregate there.
I start at 8:30 and work til 5:30. I only take 45 minutes for lunch. I refract to 1/8 D only if necessary, but it is rare that anyone is that sensitive. I find many people can be blurred by 3/4 D and still be happy with their vision.
I will agree with you that everyone is trying to do their jobs faster and that leads to some sloppiness. When it comes to refraction I really don't think that's the case though. I think there were very few who refracted to 1/8 D 20 years ago (but then, I wasn't practicing then!)
If getting an Rx accurate to .125D was necessary, would ANSI power tolerance then be .0625D?
Light travels faster than sound, which is why some people appear brighter before you hear them speak.
...and would we call it " a sixth" or " a sixtysecond" or " a sixteenth"? :hammer:...no, but it's half a twelfth, so it must be a twentyfourth.
Remember ANSI tolerances are just the sloppiest it is "suggested" one can be. With today's instant gratification society, they are erroniously being accepted as the highest achiveable standard. Very, very sad.
Chip
We still make lenses to 0.12 diopter, see some almost every day.
.12(5)
.25
.37(5) }or: 1.00/8=.125
.50
.62(5)
.75
.87(5)
1.00
I recall working in a lab when I began my optical career and the manager was calling the 8ths; 12ths. I didn't have a clue then but simple math explains it nicely.
You would think with today's advances in lab technology we'd see a higher degree of accuracy with Rx lenses. Yet every day I see lenses that are off by .125. With the old tooling, glass lenses were highly precise but plastics were a little less predictable. Now I would assume they are more exacting.
Anyhow, I think ANSI tolerances are sufficient. I certainly wouldn't want to make a fuss over .125 on power if it weren't going to make a difference in the performance on the eyewear. If all doctors refracted in .125 increments; refractions would take an hour and glasses would take 2 weeks to make.
Oh yeah, what's with an axis of 62 on a .25 cylinder??? Last I checked; the phoropter isn't that detailed.;)
Thank you, thank you, thank you. Correct is correct. And ANSI standards are only suggested. They are only the least correct and are an average of what is tolerated by a patient. I believe in striving to be right on. Have had a lot of docs in the past prescribe in 0.125 steps for patients who cannot tolerate ANSI.
Also neutralization shouldn't be according to ANSI, because it could be off according to the standards, and the original could have been off according to the standards, and then what???? Not within tolerance.
I could go on and on about this one.
Diane
Anything worth doing is worth doing well.
I've never known a Dr. to purposely refract to eighths. Every Dr. I've ran across that wrote an eighth Rx was splitting the difference between "one or two" when a patient couldn't make up their mind which was better.
What would you like us to do when the final axis is between 60 and 65? I don't see why writing down a specific axis is worse than rounding to the nearest 5 degrees. Also, depending on the phoropter, some are that detailed. Granted, no patient will notice the difference between an axis of 062 and 065 with a .25 cyl, but why change the results to get an even 5?
Does it really take you any more effort or time to set a finished lens to 62 degrees before edging?
After all the complaining of ODs being too lazy to refract accurately, I really didn't expect to see this! :D
Its amazing how I don't even think about it that way anymore hardly. It has been dumbed down and I just kind of go along with the terminology. But you are absolutely correct and I apologize for sounding like a mctician:shiner:
Ory,
You're right about the 62 degrees. Maybe us opticians are too lazy to rotate the lens a few more degrees:) . Just kidding.
I never mentioned OD's being too lazy to refract though; I think that was Chip.
In my experience, *no one* is sensitive to 0.12D. What people are sensitive to, however, is whether or not the *target* refractive findings are*right-on* the *appropriate* *sweet-spot* for that person's needs (or desires).
KEYWORDS: appropriate & sweet spot.
ANSI is just fine...its the lack of new, refractive technologies coupled with less-than-masterful listening on the part of the refractionist (and optician) that result in most of the redo's I encounter.
And even with all the above said...I still believe in the saying:
"even Joe DiMaggio didn't get a hit everytime at bat"!
Overall, if I can't "make-it-right/satisfactory" in three swings, then this person's target-needs are movin' too much for me.
Barry Santini, ABOM
Last edited by Barry Santini; 08-27-2006 at 06:18 AM.
I am surprised that the metric system hasn't taken over here.
Some lab machines can surface to 1/10, but then you need another set of laps because most of the work will be in the 1/4 diopters and some in 1/8 flavor.
Actually, it's half of an eighth, so it's a sixteenth - an old surface guy I knew was very proud of getting "that last oh oh six" as he called it - doesn't matter functionally, just a pride thing
Actually some Dr's are refracting to .10, I've seen a couple of Rx's written this way. I don't know who is making the equipment, but I applaud them.
P.S. I'm one of the people that can tell the difference between .62 (my current Rx) and .50 or .75
Metric System
As you are using the metric system in the optical field, you should not even use 1/12th or 1/8th diopter.
The whole process ended in the proclamation on June 22, 1799 of the metric system with the storage in the Archives of the Republic of the physical embodiments of the standard, the prototype metre and the prototype kilogram, both made in a platinum alloy, witnessed by representatives of the French and several foreign governments and most important natural philosophers of the time. The motto adopted for the metric system was: "for all men, for all time".
By the 1960s, the majority of nations were on the metric system and most that were not had started programmes to fully convert to the metric system (metrication). As of 2007 only three countries, the United States, Liberia, and Myanmar (Burma) had not mandated the metric system upon their populace. :p
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