##### Asked by: Everilda Legarbarrena
asked in category: General Last Updated: 14th January, 2020

# What is minimum blank size?

« Back to Glossary Index. Minimum Blank Size: (MBS) The smallest lens blank that can be used and still cut out to fit a frame. Eyewire size and patient pupillary distance will both affect the minimum size that can be used. Synonyms: ""

Similarly, what is a blank size?

Minimum Blank Size (MBS) = (GCD – PD) + ED In the examples on the previous page, the ED is the same as the A measurement since the frame illustrated is round. Therefore, the theoretically smallest lens size that can be used in Example A is 44 mm.

Likewise, wHAT IS lens blank? Noun. lens blank (plural lens blanks) A rough, opaque piece of glass of suitable size, design and composition for use, when ground and polished, as a multifocal lens for use in a pair of eyeglasses.

Keeping this in consideration, how do you calculate blank lens size?

The alternate method for calculating the minimum blank size is to measure the frame while on the wearer. The distance from the pupil centre to the widest point of the rim of the frame, then doubled, provides the minimum blank size. Don't forget to add the extra 2 mm to allow for bevel and lens edge witnesses.

How do you calculate Decentration?

The formula is Frame PD- Patient PD / 2= Decentration each eye. Example: Patient PD 68. Frame 50/20. Decentration = 1m/m each.

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