Interpupillary Distance

[ARguy]

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Hi, I'm usually over in the dental forum but was wondering if I could get a little advice from some of the eyeball experts on here. I have an IPD of 58. The high speed prescription Oakley sunglasses that I want to buy require a minimum IPD of 60. The lady at the company said it probably won't matter all that much but I want to make sure. I don't want to be getting headaches or blurred vision on long drives or in lectures (when I use the clear lenses). Anybody know if I can bump to 60 with no bad stuff going on? Or am I SOL? I appreciate the info.

 

[Ben Chudner]

Hi, I'm usually over in the dental forum but was wondering if I could get a little advice from some of the eyeball experts on here. I have an IPD of 58. The high speed prescription Oakley sunglasses that I want to buy require a minimum IPD of 60. The lady at the company said it probably won't matter all that much but I want to make sure. I don't want to be getting headaches or blurred vision on long drives or in lectures (when I use the clear lenses). Anybody know if I can bump to 60 with no bad stuff going on? Or am I SOL? I appreciate the info.

In order to answer your question, it would help to have your prescription. The amount and direction of prism induced is directly related to the power of the lens.

 

[ARguy]

OK, thanks. Here it is:

Sphere Cylinder Axis
OD -1.25 -1.00 120
OS -1.50 -1.00 074

 

[Cal_OD]

It doesn't matter what your PD or IPD or whatever you call it is. All that matters is whether or not the lens will work for your frame. If it is too curved it won't work. So lesson, choose a frame that they can put your RX in.

OK, thanks. Here it is:

Sphere Cylinder Axis
OD -1.25 -1.00 120
OS -1.50 -1.00 074

 

[ARguy]

Um, ok. They have different types of frames that will allow for different IPD's. Some will go as low as 58mm (which is what I am) but I don't want those frames. I would like the frame that will only go to 60mm. So, yes, the prescription will fit in the frames. I just want to know if since the IPD will be 60mm and not 58mm I will experience any probs if I wear them.

 

[Ben Chudner]

It doesn't matter what your PD or IPD or whatever you call it is. All that matters is whether or not the lens will work for your frame. If it is too curved it won't work. So lesson, choose a frame that they can put your RX in.

This is an Rxable frame so I am sure it can take a lens with a standard base curve.

 

[Ben Chudner]

OK, thanks. Here it is:

Sphere Cylinder Axis
OD -1.25 -1.00 120
OS -1.50 -1.00 074

Since I don't feel like calculating the exact power along the 180, this is only an estimate, but your prescription with a 60 pd will induce approximately 0.4D of base in prism. The actual number is a tiny bit higher, but this is close enough. This is small enough that you should not have any eyestrain, in fact it's within ANSI standards for induced prism. So go for it.

 

[rpames]

It doesn't matter what your PD or IPD or whatever you call it is. All that matters is whether or not the lens will work for your frame. If it is too curved it won't work. So lesson, choose a frame that they can put your RX in.

I'm not quite sure what you mean by this, but PD is incredible important in an SRx. It is vital to the prescription.

I do agree with Ben, your power is low enough that 2 mm will not make a huge difference. You shouldn't have a problem.

 

[sethuel1]

Um, ok. They have different types of frames that will allow for different IPD's. Some will go as low as 58mm (which is what I am) but I don't want those frames. I would like the frame that will only go to 60mm. So, yes, the prescription will fit in the frames. I just want to know if since the IPD will be 60mm and not 58mm I will experience any probs if I wear them.

which frames are we talking about, by the way?

 

[ARguy]

Thanks guys! I'll go ahead and order my sweet new shades today. I'm getting the half jackets.

 

[Ryan_eyeball]

This is a thread I would post this in. I work part time on weekends at Target Optical (which I'm quitting in three weeks, cuz I want a break before graduation). Well anyways, a patient came in saying she was having trouble seeing out of her glasses. Her was this

-2.00 -0.25 x 180 OU

Her PD on the order form was 65mm. Well whenever the optician (wasn't me =0)
put the order in she had put in for a pd of 40mm. I'm surprised the lab didn't even call to confirm this. lol Many kids I've seen have at least a pd of 50 to 57mm. So talk about major prism adaptation. We got those remade for her at no charge.

 

[ARguy]

Wow, that seems pretty off. How do you calculate how far from the ideal IPD can be and still give the correct adjustment? I'm curious now as to how it works. For instance, Ryan Eyeball's patient with the stronger Rx than mine, could she use an IPD that was within plus or minus 2mm of her actual 65mm or would it totally screw up the Rx?

 

[UABopt]

Wow, that seems pretty off. How do you calculate how far from the ideal IPD can be and still give the correct adjustment? I'm curious now as to how it works. For instance, Ryan Eyeball's patient with the stronger Rx than mine, could she use an IPD that was within plus or minus 2mm of her actual 65mm or would it totally screw up the Rx?

It's fairly simple you multiply the decentration in cm by the power (in Diopters) in the meridian which you are interested (in the case of specs normally 180) and this will give you the displacement in prism diopters. Do that for each lens and then calculate the total prismatic effect. If the PD is too small for the person the optical center is displaced nasally. This will create a Base out effect with negative lenses and BI effect on positive lenses. If the spec PD is too big for the persons PD the optical center will be temporal to the person's line of sight and the opposite will be true.

A normal person can actually tolerate quite a bit of BI and BO prism. We are much more sensitive to BU and BD prism i.e. vertical prism. The thing is as long as you are not an anisometrope (different refractive error in each eye) and as long as the lenses are not displaced by different amount you will have 0 net prismatic effect in the vertical direction. Vertical prismatic effect can be a big problem in an anisometropia though.

 

[ARguy]

It's fairly simple you multiply the decentration in cm by the power (in Diopters) in the meridian which you are interested (in the case of specs normally 180) and this will give you the displacement in prism diopters. Do that for each lens and then calculate the total prismatic effect. If the PD is too small for the person the optical center is displaced nasally. This will create a Base out effect with negative lenses and BI effect on positive lenses. If the spec PD is too big for the persons PD the optical center will be temporal to the person's line of sight and the opposite will be true.

A normal person can actually tolerate quite a bit of BI and BO prism. We are much more sensitive to BU and BD prism i.e. vertical prism. The thing is as long as you are not an anisometrope (different refractive error in each eye) and as long as the lenses are displaced by different amount you will have 0 net prismatic effect in the vertical direction. Vertical prismatic effect can be a big problem in an anisometropia though.

Say Whaaaa? 😕

 

[UABopt]

Say Whaaaa? 😕

LOL sorry... it seemed so simple when I typed it out... but I suppose if you had very little background in optics it would not at all be clear.

So with out being too in depth... The reason we are concerned with PD is that if you have a pair of glasses and you are not looking through the "optical center" you will induce what is known as prismatic effect. A prism basically shifts light (it makes it look like it is coming from a different direction), without changing the vergence. By vergence I mean it does not diverge light (a negative vergence) or converge light (a positive vergence). prismatic effect is measured in prism diopters which is defined as the distance light is shifted in cm divided by the distance the light has traveled in M.

So here is the main point of concern... the further you are away you are from looking through the optical center... i.e. the further away your PD is away from the "spectacle PD" and the stronger the lenses are that you are looking through the more prismatic effect you are going to induce. The net result of unwanted prismatic effect is that you would become diplopic... that is to say you would see 2 images rather than 1 fused image.

Prism though, is not always a bad thing. Prism is often used in patients who have binocular vision problems, ie.. eso or exotropia or phoria (crossed eyes, turned eye etc). Without prism (or extra minus or plus but we won't wont go into AC/A) in their lenses these patients would see double.

In your case very little prismatic effect would be induced mainly because your PD is not that far away from the spectacle PD and because your Rx is not very strong.

So that's it in a nutshell sorry I could not be clearer.

 

[ARguy]

LOL sorry... it seemed so simple when I typed it out... but I suppose if you had very little background in optics it would not at all be clear.

So with out being too in depth... The reason we are concerned with PD is that if you have a pair of glasses and you are not looking through the "optical center" you will induce what is known as prismatic effect. A prism basically shifts light (it makes it look like it is coming from a different direction), without changing the vergence. By vergence I mean it does not diverge light (a negative vergence) or converge light (a positive vergence). prismatic effect is measured in prism diopters which is defined as the distance light is shifted in cm divided by the distance the light has traveled in M.

So here is the main point of concern... the further you are away you are from looking through the optical center... i.e. the further away your PD is away from the "spectacle PD" and the stronger the lenses are that you are looking through the more prismatic effect you are going to induce. The net result of unwanted prismatic effect is that you would become diplopic... that is to say you would see 2 images rather than 1 fused image.

Prism though, is not always a bad thing. Prism is often used in patients who have binocular vision problems, ie.. eso or exotropia or phoria (crossed eyes, turned eye etc). Without prism (or extra minus or plus but we won't wont go into AC/A) in their lenses these patients would see double.

In your case very little prismatic effect would be induced mainly because your PD is not that far away from the spectacle PD and because your Rx is not very strong.

So that's it in a nutshell sorry I could not be clearer.

Cool, thanks! That was an extremely good explanation. There is definitely an art to "dumbing it down" so others can understand. You my friend have a gift. Today I have truly learned something. 😀