If you are specifying an optical center height...

**Happylady** · 10-21-2006, 07:03 PM

If you specify an optical center height, how do you place it in relation to the pupil? Do you drop it a few millimeters depending on the panoscopic tilt?

How often do you specify an optical center height with todays narrower frames? Does it depend on the lens material or the prescription?

**Samuel Jong** · 10-21-2006, 08:30 PM

Originally Posted by Happylady

If you specify an optical center height, how do you place it in relation to the pupil? Do you drop it a few millimeters depending on the panoscopic tilt?

How often do you specify an optical center height with todays narrower frames? Does it depend on the lens material or the prescription?

I am also interested to hear it.

**Framebender** · 10-21-2006, 08:48 PM

Fortunately single vision kids aren't into frames with big B measurements. The old guys still wearing those are all in some sort of multifocal. We are doing more of it with motorcycle eyewear. When we do it we spot it just like a progressive and run the OC there. So far it hasn't bit us.
:cheers:

**Jacqui** · 10-21-2006, 08:53 PM

Several of our customers are doing it like Framebender is. One says he spots at the bottom of the pupil. All use mono PD's.

**optical24/7** · 10-23-2006, 12:01 PM

We utilize MRP's when we have Rx imbalances and/or higher powers. Frame selection is the most important factor. I don't like to raise the MRP much over the geo center of the frame due to imbalanced thickness that results on the lower half of the lens. (myopes). I have a demo pair made up to explain to patients how this pair or that pair will make a more cosmetically pleasing final product. We place MRP's at the lower edge of the pupil (after frame adjustment ).

**Grubendol** · 10-23-2006, 12:03 PM

we use OC on all 1.67 orders. Generally it's for our aspheric/high power orders. And we always compensate for panto of the frame.

**FVCCHRIS** · 10-23-2006, 12:35 PM

Proper O.C. placement is always desirous on your higher minus patients but you need to be on the lookout for those parients who are high powered and have become accustomed to fair amounts of yoked prism due to years of wearing O.C.'s at the G.C. and wearing glasses that fit low on the face. You may cause a problem when you put that O.C. "where it should be". You know those people you try to help and you open up a can o' worms.:bbg:

**Bezza** · 10-23-2006, 12:37 PM

OC heights should be taken for all aspheric lenses and all Rxs over about +/- 5.00DS and of course any multifocals, it is also improtant for anisometropic Rxs. I will fail ABDO exams if i do not do this and I believe it is included in BS2738 somewhere too.

**Bezza** · 10-23-2006, 12:43 PM

Originally Posted by FVCCHRIS

Proper O.C. placement is always desirous on your higher minus patients but you need to be on the lookout for those parients who are high powered and have become accustomed to fair amounts of yoked prism due to years of wearing O.C.'s at the G.C. and wearing glasses that fit low on the face. You may cause a problem when you put that O.C. "where it should be". You know those people you try to help and you open up a can o' worms.:bbg:

I agree, being a high myope myself I have first hand experience of this, I would recommend checking the OCs of their current glasses, seeing where they sit in relation to the PXs pupils and doing your own measurements before you decide where to fit them. Although probably 9/10 times I would fit them where I measure them unless I was expecting problems of this kind.

**Happylady** · 10-23-2006, 06:56 PM

If you do an OC, do you put it right in front of the pupil or do you drop it a few millimeters based on the tilt of the frame?

**Bezza** · 10-23-2006, 07:53 PM

Originally Posted by Happylady

If you do an OC, do you put it right in front of the pupil or do you drop it a few millimeters based on the tilt of the frame?

in an ideal situation i would prefer to have the frame set up correctly including pantoscopic tilt before measuring, that way you know that you have got it right. However adjusting frames in front of patients is not an ideal situation and neither is spending the extra time to to and fro from wherever you do your adjustments during a dispense. In practice i tend to measure OC heights either on pupil centre or a little below pupil centre if its a first time vari wearer.
Remember that if you increase the pantoscopic tilt of the frame you will effectively drop the OC heights of the finished lenses slightly.

**Gary Falk** · 10-24-2006, 06:59 AM

You should drop the OC height 1mm for every 2 degrees of pantoscopic tilt to align the lens at the center of rotation of the eye.
Another way to measure this is to have the patient tilt their head back until the pantoscopic tilt is zero and then measure the OC height.

**Happylady** · 10-24-2006, 09:30 AM

Originally Posted by LENSDUSTER

You should drop the OC height 1mm for every 2 degrees of pantoscopic tilt to align the lens at the center of rotation of the eye.
Another way to measure this is to have the patient tilt their head back until the pantoscopic tilt is zero and then measure the OC height.

This is what I had thought. So a frame with a normal tilt of 10 degrees or so should have the optical center placed about 5 mms below the pupil center.

I wonder if most people drop it.

**EyeFitWell** · 10-24-2006, 09:51 AM

I do an OC ht on a strong Rx (about 6 or more plus or minus), if the pt wears their glasses in an unusual way (down the nose, etc), or when the frame fits such that the eye is not on the datum. If it's -0.25, I wouldn't bother. I have a hard time getting my lab to notice that I've specified an OC ht on SV (I guess it's unusual for them) and frequently they're sent to me with the OC in the center and must be returned and remade.

**Echo419** · 10-24-2006, 10:18 AM

I agree, on high pwrs 4.75 and up especially in high index I set 3mm below pupil, On high aniso's I might set closer to pupil especially on polys or High index.

**Grubendol** · 10-24-2006, 10:25 AM

I always use the panto formula mentioned by the Duster

**CME4SPECS** · 10-24-2006, 04:15 PM

Do you all request an OC height on PAL'S??

**Grubendol** · 10-24-2006, 04:46 PM

PAL's get pupil height, not OC.

**CME4SPECS** · 10-24-2006, 05:38 PM

Originally Posted by Grubendol

PAL's get pupil height, not OC.

So do you feel that OC height is only important on SV and FT?

**Samuel Jong** · 10-24-2006, 05:52 PM

Originally Posted by EyeFitWell

I do an OC ht on a strong Rx (about 6 or more plus or minus), if the pt wears their glasses in an unusual way (down the nose, etc), or when the frame fits such that the eye is not on the datum. If it's -0.25, I wouldn't bother. I have a hard time getting my lab to notice that I've specified an OC ht on SV (I guess it's unusual for them) and frequently they're sent to me with the OC in the center and must be returned and remade.

Do you ask the lab to place the OC above or below the datum line?

**Grubendol** · 10-24-2006, 05:55 PM

Originally Posted by CME4SPECS

So do you feel that OC height is only important on SV and FT?

Well by the nature of the design on a progressive, something akin to OC is necessary to have the lenses work at all for the patient. But it is not OC, it is Pupil Height.

**CME4SPECS** · 10-24-2006, 06:17 PM

Originally Posted by Grubendol

Well by the nature of the design on a progressive, something akin to OC is necessary to have the lenses work at all for the patient. But it is not OC, it is Pupil Height.

Actually we place the MRP in relation to the pupil and do not take the OC into consideration on PALS. And we don't seem to have problems with that. In fact we put base down prism in PALS to balance out the thickness of the lenses. If the PAL is plus you are actually moving the OC further down from where the wearer is looking through the lens in distance. Minus lenses with BD prism move the OC up more towards the MRP.
How about trifocals? I put the OC at 180* and don't have any problems with that either. Once again to balance the thickness.
Maybe some of you are fitting frames to low like the picture of the little girl in an active thread here.

**Grubendol** · 10-24-2006, 06:19 PM

The lens designs are supposed to take the prism effect into consideration on plus lenses, at least that's what my progressive class at Expo said. Correct me if I'm wrong...>Darryl? Pete?

**EyeFitWell** · 10-27-2006, 08:33 AM

Originally Posted by Samuel Jong

Do you ask the lab to place the OC above or below the datum line?

Depends on where the pupil is!
Here's a recent example:
Pt rx roughly +7.75 both eyes. Frame's B measurement around 30. Pt wears glasses LOW so her pupil sits around 27mm from the bottom of the frame, 3mm from the top. Literally, it looks like she's looking over them, I can't believe she can see this way! If I put the OC at 15, she's not going to see well. I know this for sure on her b/c LC did it to her before she came to see me. So in this case, the answer is above the datum. But if someone insists on wearing their glasses so their pupil is significantly below the datum and the rx is strong enough to matter, then I would again set it where the pupil sits in the frame (taking into consideration the panto formula).

**CME4SPECS** · 10-27-2006, 11:26 AM

Originally Posted by EyeFitWell

Depends on where the pupil is!
Here's a recent example:
Pt rx roughly +7.75 both eyes. Frame's B measurement around 30. Pt wears glasses LOW so her pupil sits around 27mm from the bottom of the frame, 3mm from the top. Literally, it looks like she's looking over them, I can't believe she can see this way! If I put the OC at 15, she's not going to see well. I know this for sure on her b/c LC did it to her before she came to see me. So in this case, the answer is above the datum. But if someone insists on wearing their glasses so their pupil is significantly below the datum and the rx is strong enough to matter, then I would again set it where the pupil sits in the frame (taking into consideration the panto formula).

You are saying that you fit the seg 27 hi. Correct? Terrible frame choice, by the way! But were is the OC? If it is also at 27, those lenses are as thick as a brick at the top!