1. What is Minimum Lens Blank Size?

The Minimum Blank Size (MBS) is the smallest lens blank that can be used to produce a finished lens that meets the patient's prescription and frame requirements. It ensures proper lens centration and edge thickness.

2. How Does the Calculator Work?

The calculator uses the MBS formula:

Where:

• \( ED \) — Effective diameter of the frame (mm)
• \( Decentration \) — Amount of decentration needed (mm)
• The additional 2mm is a safety margin

Explanation: The formula accounts for the frame size, how much the optical center needs to be moved, and adds a small buffer for manufacturing.

3. Importance of MBS Calculation

Details: Calculating MBS helps opticians select the appropriate lens blank size, reducing material waste and ensuring proper lens thickness and optical performance.

4. Using the Calculator

Tips: Measure the frame's effective diameter and calculate decentration based on patient's PD and frame measurements. Enter values in millimeters.

5. Frequently Asked Questions (FAQ)

Q1: What is effective diameter (ED)?
A: ED is the longest diagonal measurement of the lens shape, typically 2-4mm larger than the frame's A measurement.

Q2: How is decentration calculated?
A: Decentration = (Frame PD - Patient PD)/2, where Frame PD is the distance between frame geometric centers.

Q3: Why add 2mm to the calculation?
A: The 2mm buffer ensures there's enough material for edging and minor adjustments during lens fabrication.

Q4: Can I use a smaller blank than the MBS?
A: Using a smaller blank may result in edge defects, excessive edge thickness, or inability to properly position the optical center.

Q5: Does this apply to all lens materials?
A: Yes, the MBS calculation applies to all materials (CR-39, polycarbonate, high-index, etc.), though some materials may have specific blank size increments.