How much to reduce the PD for close up?

How much would you reduce the PD when working at around 70-80cm? (There is some CYL involved )

  • 0
  • 1mm
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  • 4mm

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There is not enough information provided to accurately guess a reply to this question.

The best way to find any PD value is to measure it directly with a pupilometer, digital centration device, or a millimeter ruler. Failing that you can estimate it via calculation (taking into account the effect of prism and near convergence) if you know each eye’s monocular distance PD value, the target working distance, and the focal power of the lens.

In any case, unless you have a very large distance PD and high lens power, it should be a very small change at 80cm. 0-2mm is likely.

For example, my binocular distance IPD is pretty large at 68 (-6.50 diopters) and I’m seeing about a 2mm drop in PD for my differentials at +1.25 diopters (80cm working distance).

That said, some recommend just using your distance PD for differentials so can more easily reuse them as normalized later. Though that can be problematic as well. For example, if your PD is too wide, it can cause excess “base in” prism which may cause the eyes to diverge, leading to headaches, eye strain, and other problems. Though with 2mm or less of difference, this is not likely a major concern unless you need very high diopter correction.

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Thanks for the reply, just to give some context my normalized are L: -1.25 R: -3.50, -1.00 170° at 68mm PD
and diffs are L: 0, R: -2.25 -0.75 170°

And I won’t be using them as normalized cuz by then I should have no astigmatism…

I ordered glasses -7.50, -2.00 180* for close up with distance PD of 62 mm and it looked good.

How did you know there was no change, have you got it measured?