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Calculator

Dispensing calculator

Work out frame PD, decentration per lens, minimum blank size and where the seg or optical centre sits, from the frame’s boxing measurements and the patient’s PD.

Frame and patient

Boxing measurements
Patient PD
Lens

Heights are measured up from the lowest point of the lens box. Leave ED or B blank if you only need part of the answer.

Results

Frame PD (A + DBL)
72 mm
Total decentration
10 mm in
Decentration per lens
5 mm in
Seg placement
2 mm below
Minimum blank size68 mmExam answer
With edging allowance70 mm+ 2 mm, as many labs order

Working

  • Frame PD 72 − PD 62 = 10 total; ÷ 2 = 5 per lens
  • MBS = ED + 2 × 5 = 68
  • Seg height − B ÷ 2 = 2 mm below

Where everything sits

ODOSDBL 18
Viewed from the front, so the patient’s right eye (OD) is on your left. The small cross is each box centre, the dot is where the pupil and optical centre go, and the arrow shows the decentration. The dashed line is the datum line; the solid bar is the top of the seg at the seg height.

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