Do the aspheric can simply move patient's PD in order to reduce the edge thickness

**cnet_baby** · 12-20-2005, 12:37 PM

is it possible i move the patient's PD when i was edging the lens in order to reduce the edge thickness for the aspheric lens ??? there say aspheric lens is steeply curve no suitable to decentration.

**Andrew Weiss** · 12-20-2005, 01:37 PM

I'm not sure I'm answering your question, but here goes:

Aspheric design lenses require more care in placing the optical center over the pupil in both the horizontal and the vertical meridians. I would not move the optical center aay from the pupil in order to thin out the edge of the lens.

I hope this helps. If this does not answer your question, I would ask that you give more specific information.

**QDO1** · 12-20-2005, 01:47 PM

Originally Posted by cnet_baby

is it possible i move the patient's PD when i was edging the lens in order to reduce the edge thickness for the aspheric lens ??? there say aspheric lens is steeply curve no suitable to decentration.

Aspheric lenses need proper centering, you cant move the lens to make it thinner - you will just interfeer with the quality of vision achievable out of the lens. if the lens needs prism, then it must be surfaced

**cnet_baby** · 12-20-2005, 01:55 PM

Originally Posted by QDO1

Aspheric lenses need proper centering, you cant move the lens to make it thinner - you will just interfeer with the quality of vision achievable out of the lens. if the lens needs prism, then it must be surfaced

patient'S power

R:-8.50-1.75x90
L:-9.50-1.50x90

i know that aspheric is steeply curve not necessary to do decentration , but can i just move Patient's PD to give it more thinner????

patient's lens is 1.6 aspheric
For example Frame PD :70 ,Patient's PD :62, but i try to move Patient's PD to: 68, i purpose want to make edge thickness become thinner. is it possible , why???

**cnet_baby** · 12-20-2005, 01:57 PM

Originally Posted by Andrew Weiss

I would ask that you give more specific information.

thanks for your feedback , so what specific information you want???

**QDO1** · 12-20-2005, 02:01 PM

Originally Posted by cnet_baby

patient'S power

R:-8.50-1.75x90
L:-9.50-1.50x90

i know that aspheric is steeply curve not necessary to do decentration , but can i just move Patient's PD to give it more thinner????

patient's lens is 1.6 aspheric
For example Frame PD :70 ,Patient's PD :62, but i try to move Patient's PD to: 68, i purpose want to make edge thickness become thinner. is it possible , why???

nope - set the mono OC's to the same as the mono PD's for the patient, and get the height of the OC right too. If you want thinner, why not higher index, or smaller frame?

**cnet_baby** · 12-20-2005, 02:06 PM

Originally Posted by QDO1

nope - set the mono OC's to the same as the mono PD's for the patient, and get the height of the OC right too. If you want thinner, why not higher index, or smaller frame?

you are right , but the patient hav budget to make a spec, is it possible to use my matter????? what effect will cause ??? can u explain to me, i want to know more about it , thank you

**QDO1** · 12-20-2005, 02:37 PM

Originally Posted by cnet_baby

you are right , but the patient hav budget to make a spec, is it possible to use my matter????? what effect will cause ??? can u explain to me, i want to know more about it , thank you

sorry i dont understand the question

**mattress** · 12-20-2005, 03:19 PM

would create unwanted prism

**SpecialT** · 12-20-2005, 03:49 PM

You can't change the patients PD on any lens without a prescription for prism. Aspheric lenses are no exception to this rule. In fact, you should be even more exact with an aspheric lens.

Why... decentering a lens creates prism which can cause double vision or an eye turn. This will get you in big trouble (simply put).

In short, do as the doctor tells you.

**Andrew Weiss** · 12-20-2005, 04:54 PM

Originally Posted by cnet_baby

thanks for your feedback , so what specific information you want???

You gave the information I wanted with the Rx. You do NOT want to decenter the lens away from the pupil for two reasons: 1) you induce unwanted prism, which the doctor did not prescribe and which you cannot prescribe; 2) the patient's vision will be compromised because the asphericity of the lens will be incorrectly positioned vis-a-vis the pupil.

In general, I would never decenter a lens for thinness. It is far more important, IMHO, to fit the OC at the pupil and give the patient the best possible vision.

**Jedi** · 12-20-2005, 05:13 PM

Originally Posted by cnet_baby

you are right , but the patient hav budget to make a spec, is it possible to use my matter????? what effect will cause ??? can u explain to me, i want to know more about it , thank you

You can use this calculator to figure out how much prism you will induce.
Opticampus Induced prism calculatorI'm very concerned that you are dispensing to a high myope (anyone really) without realizing the potential problems you could be causing, in regards to placement of an aspheric lense. I really hope this is not a reflection of your actual abilities or business practices.
Also with the vast amounts of lens suppliers out there I'm surprised you can't procure a budget 1.67 lens or even find a cheaper frame. Whatever you do, don't compromise this client's vision.

**Lewy** · 12-21-2005, 04:37 AM

Originally Posted by Jedi

You can use this calculator to figure out how much prism you will induce.
Opticampus Induced prism calculatorI'm very concerned that you are dispensing to a high myope (anyone really) without realizing the potential problems you could be causing, in regards to placement of an aspheric lense. I really hope this is not a reflection of your actual abilities or business practices.
Also with the vast amounts of lens suppliers out there I'm surprised you can't procure a budget 1.67 lens or even find a cheaper frame. Whatever you do, don't compromise this client's vision.

It appears you don't understand the very basics of our profession. On that level of correction any self respecting optician wouldn't settle for anything less than perfect. If as I guess you are a technician, I suggest you speak with the prescribing optician to see what criteria you can work to. If the highest index has been ordered then the lens thickness will be as it comes out, NO LESS. As you will have seen in previous postings there are many factors that govern the whole process. Lens material and design, size and shape of frame, facial measurements etc. Without this holistic approach it's going to be very difficult for us to help as much as we would like.

Sorry I cannot be there with you.

Lewy

**QDO1** · 12-21-2005, 05:00 PM

I wrote a guide to dispensing aspherics..

http://www.optiboard.com/forums/show...024#post124024

Hope this helps

**William Stacy O.D.** · 12-26-2005, 02:24 PM

Originally Posted by cnet_baby

is it possible i move the patient's PD when i was edging the lens in order to reduce the edge thickness for the aspheric lens ??? there say aspheric lens is steeply curve no suitable to decentration.

You must not do this. If you do, you are inducing prism. This is unwanted and unprescribed prism. It means YOU are prescribing prism for the patient, and at least in California, you need to be an O.D. or an M.D. to do that. Having said that, you could call the prescriber and ask if (calculate the amount using Prentice's rule) would be ok for this patient. If the patient doesn't have binocularity, or defective binocularity, he/she might change the Rx to accommodate you. Otherwise, don't do it.:finger:

**QDO1** · 12-26-2005, 02:28 PM

Originally Posted by William Stacy O.D.

You must not do this. If you do, you are inducing prism. This is unwanted and unprescribed prism. It means YOU are prescribing prism for the patient, and at least in California, you need to be an O.D. or an M.D. to do that. Having said that, you could call the prescriber and ask if (calculate the amount using Prentice's rule) would be ok for this patient. If the patient doesn't have binocularity, or defective binocularity, he/she might change the Rx to accommodate you. Otherwise, don't do it.:finger:

besides inducing prism, there are other issues - see this post about dispensing Aspherics http://www.optiboard.com/forums/showthread.php?t=15137

**William Stacy O.D.** · 12-26-2005, 02:56 PM

Originally Posted by QDO1

besides inducing prism, there are other issues - see this post about dispensing Aspherics http://www.optiboard.com/forums/showthread.php?t=15137

True. My response really is directed to doing this with ANY kind of lens. I know it could be tempting as I used to do some finishing work and used a lot of stock uncuts. As an O.D. I found myself trying to talk myself into a little prism here or there... (one reason I dumped my lab)

**QDO1** · 12-26-2005, 03:10 PM

Originally Posted by William Stacy O.D.

True. My response really is directed to doing this with ANY kind of lens. I know it could be tempting as I used to do some finishing work and used a lot of stock uncuts. As an O.D. I found myself trying to talk myself into a little prism here or there... (one reason I dumped my lab)

I think dispensers fall into 2 camps - those who disregard optics to achieve the ultimate (thinnest) lens, or those that measure mono everything, adjust RX's for position of wear, and accept a slightly thicker lens is worth it for "ultimate" optics. The second sort know when to tweak what they do to achieve both. the first sort dont really understand whats going on at all

**HarryChiling** · 12-26-2005, 04:33 PM

Unwanted Prism is a consequence of decentering a lens incorrectly in an aspheric lens, also the fact that the base curve changes as you move away from the center with an aspheric lens. Usually this is done to compensate for abberations and to thin out the lens, if you were to decenter it incorrectly you would induce prism and change the power of the lens. My suggestion would be to let the patient know tht this is the thinnest with tht material and frame, then offer them other options. Some of the available options have already been discussed, smaller frames (the smaller the lens and decentration the thinner), higher index lenses (we live in a world with 1.74 index), and also putting AR on the lens helps mask some of the thickness. I am sure if you offer your patient the options that are available and then tell them that comprimising optics is not an option in your proffesion.