Prism

[LENNY]

I got an RX today

OD +0.50 1 BU
OS +0.50 1 BU
The RX was from an OD
It looked a litle bit strange
First i thought that prisms are in opposite dirrection and she made a mistake
So i called her to verify.
She confirmed the Rx
Could anybody explain why she gave it to 10 years old child?
Help

[chip anderson]

Probably Medicaid would pay more for the glasses or the exam. Possibly she made a mistake. Maybe the patient has trouble raising her head, but I doubt 1 diopter would help.

[LENNY]

Nope
Not Medicaid
Normal 10 years old boy.
Not a mistake.

[NC-OD]

Lenny,

I've got to agree with Chip on this one. That does sound unusual.

Some VT and pediatric OD's routinely prescribe something like +0.50 or +0.75 for accommodative deficiency for use up close only,...as in reading.

Maybe this is what this OD was going for. I suppose the prism could help move the eyes down on accommodative/convergence??.... but it's such a small amount......... I don't think I would ever prescribe this.

[David Wilson]

Yoked prism such as this is a common tool of "behavioral optometrists". I am not too familiar with how they use it, only that they do. As you suggest, though, it does not seem likely that one prism diopter would have a significant effect on direction of gaze.
Regards
David Wilson

[LENNY]

I think she DID mention this term!!!!

Where can i learn about it?
I always like to find out that i am wrong in thinking that somebody else is wrong!!:drop:

[Rich R]

I've seen some patients usually with a low minus rx like -.50 ou, saying they get glare from overhead lights in the shop, by adding a slight prism both up or down gets rid of the glare, any one else ever used this, worked for me.
Rich R.

[David Wilson]

Lenny,
Yoked prism is prism prescribed where there is no differential prismatic effect, that is, in the same direction in both eyes. Eg base in RE and base out LE or, as in this case, base up in both eyes. How it is used by behavioral optometrists I'm not sure. It may also be used by non behavioral (normal, no offence meant) optometrists for similar reasons. For example, as NC OD mentioned, pediatric cases.

High powered yoked prism has been used in cases of hemianopia (where the patient has lost 50% of their field of view). It displaces the images from the 'blind' side into their useable field.

Rich,
Prism certainly can affect reflections, as Darryl has pointed out previously when discussing prism thinning in progressives. Your use of prism is an interesting one. Presumably it is used in conjunction with multicoat antireflection.

Regards
David Wilson

[Duane Metcalfe]

I can't add much here except I first experienced it while in Alaska in early 90's. The Army/Air Force OD's would prescribe, but couldn't offer a reasonable 'phone' explanation...just do it. Never had a problem with results on patient. :hammer:

[Texas Ranger]

Just a thought, vertical optical centers are cut on the geometric 180 line, while the horizontal optical centers are decentered for PD. So, many times the pt is looking several mm over the vertical OC, therefor looking through base down prism, so the doctor may just be trying to eliminate this base down prism by prescribing base up prism, so the pt really isn't looking through prism. Same goes for doing base down prism on executive bifocals with plus power, etc.

[David Wilson]

Al,
It would be base down for hyperopes but base up for myopes in the situation you describe. However, it does raise an interesting point, that is, the heights for single vision lenses. They should all be fitted according to the centre of rotation rule. That is, the OC should be dropped 1mm for every two degrees of pantoscopic tilt so that the principal axis of the lens passes through the centre of rotation of the eye. We are aware of this rule for aspherics but it also applies to 'normal' lenses. In the past we have fitted lenses on datum (the horizontal centre line) which, as you say Al, is usually below the client's pupil centre. So, we have been close to the right position by accident.

Regards
David Wilson

[LENNY]

BTW
I dispensed te glasses!
Pure boy did not have any clue what they are for!
Had to explain him for 20 min
I doubt he will ever use them as reading glasses!
:hammer:
My only hope is he has to go back to the Dr in 6 month so i will probably redo the glasses for -0.75 OU that he was wearing before

[Alir82]

Hello Lenny -

I work for a pediatric office where we use this type of prism on a regular basis. The vertical yoked prism is to help with kids who have either spacial awareness issues, or visual perseption issues, and sometimes both. Base up prism helps to lower down gaze, which in turn helps with convergence. This is especially helpfull if a child has a convergence insufficency and is having difficulty with school work.

I don't know if that's what you were looking for but I hope it helps.

[obxeyeguy]

09-24-2001, 07:55 PM

Welcome to Optiboard! This was the date of the origional post, almost 8 years ago. Not a record, but close!;)

[Wes]

Wonder what the record is?

[Senorwes1]

I used to see these types of Rx's all the time at my previous location from an OD who had researched yoked prism while in Optometry school and found out it could help some people. He only prescribed BU or BD in both eyes, he never did BI/BO. He mainly prescribed it for kids and people (teenagers up to presbyopes) who hold their reading material about 6 inches from their nose in order to read. He would hand them a book or a magazine and if they held it really close to their face to read it, and were otherwise seeing well, he would prescribe yoked prism. He explained it to me one day and I can't remember word for word what he said but it made sense to me when he explained it. Sometimes he would prescribe plano with 1.5BU or plano with 1.5BD in both eyes and just by looking through the lenses, they appeared to have the characteristics of plus lenses because they seemed to magnify and displace objects. A lot of people in the opticial field think that this kinda stuff is crazy and only quacks would do something like this but it actually did work for a lot of our patients. My opinion is if it helps one person, then great, even though it may not work for everybody. He would always tell patients if they went to see another Dr for their next exam that they would not get the same type Rx from any other Dr and he would tell them to remember the word "prism." I think it was wise that you called to verify the Rx because I have also had it happen when the "tech" wrote out the Rx and wrote the prism incorrectly. Ask your patient if he/she can tell a difference with the Rx and see how the Dr. explained it to him/her. This kind of stuff is very interesting, it's like optical witchcraft.

[Ian Jordan]

prism not only changes position, it also has a small effect on image size orientation.
Therefore visio spatial awareness can be modified and it can be of use in numerous conditions
google Kaplan yoked prism

Must admit we stopped using this technique about 10 years ago though when we found other methods were much better

[chip anderson]

Senor:

Have you ever of a doctor (M.D. or OMD) who did not have a financial interest in dispensing ever prescribing yoked prism? If so was it for anything other than a paralized patient. Ever heard of an eye doctor who didn't dispense being indited for medicaid or medicare fraud?

[HarryChiling]

Yoked prism such as this is a common tool of "behavioral optometrists".

I got an RX today

OD +0.50 1 BU
OS +0.50 1 BU

So if I'm reading this correctly, children if your behavior doesn't improve your optometrists is going to yolk you up.

Sorry couldn't help myself, you can flame the post all you want I got it outta my system.
PS - Yes it took me 8 years to come up with that.