# Thread: What is the minimum blank size for this Rx and PD?

1. ## What is the minimum blank size for this Rx and PD?

What is the minimum blank size for this computer use prescription?

OD: -0.75 -1.75 x 165
OS: -1.75 -0.75 x 030

Patient's PD is 58

Frame PD is 55, bridge is 18, and ED is 59 measured from inner to inner.

Do I have to move the PD in for INT use?

2. Power makes no difference unless you’re figuring how much you can *cheat* on decentration (altering the OC placement due to low prismatic value at 180). Frame PD - patients PD + Lens ED. With the above info:

55 (eye size) + 18 (dbl) = 73 - 58 (patient PD) = 15 + 59 (ED) = 74. Some recommend going at least 1mm larger than the formula, so 75mm would be the minimum size stock lens for cut out.

As far as PD comp for intermediate, usually 1mm for computer distance is good, but verify the distance of intended use and comp from there.

Power makes no difference unless you’re figuring how much you can *cheat* on decentration (altering the OC placement due to low prismatic value at 180). Frame PD - patients PD + Lens ED.
Power does​ make a difference insofar as minus lenses tend to come in 70mm blanks and plus in 65. But I knew what you meant; carry on...

4. Originally Posted by AngeHamm
Power does​ make a difference insofar as minus lenses tend to come in 70mm blanks and plus in 65. But I knew what you meant; carry on...

5. Also important to know: extreme OC heights can affect this data as well. That 65mm blank may cut out perfectly with a center OC, but raise it a few millimeters and you may not get cutout.

Power makes no difference unless you’re figuring how much you can *cheat* on decentration (altering the OC placement due to low prismatic value at 180). Frame PD - patients PD + Lens ED. With the above info:

55 (eye size) + 18 (dbl) = 73 - 58 (patient PD) = 15 + 59 (ED) = 74. Some recommend going at least 1mm larger than the formula, so 75mm would be the minimum size stock lens for cut out.

As far as PD comp for intermediate, usually 1mm for computer distance is good, but verify the distance of intended use and comp from there.
Do you have to add 1 or 2mm for certain lens type or prescription? Like if it's for reading glasses?

7. Originally Posted by Optician53
Do you have to add 1 or 2mm for certain lens type or prescription? Like if it's for reading glasses?
RX shouldn't have anything to do with it. But I've found that some edgers, like the Santinelli LE1000 I'm currently using, are more "conservative" with their tracing. I add 1 or 2 because of that.

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