High Myopia (-6.00D & Beyond): Edge Thickness, Minification & Index Optimization

A minus lens (concave) designed to correct myopia is naturally thinnest at the optical center and thickens parabolically toward the outer perimeter. The amount of peripheral edge thickness is dictated by the Sagitta Formula ($s = r - \sqrt{r^2 - y^2}$), where thickness increases exponentially with lens diameter ($y$).

Understanding this reveals the #1 secret for high-myopia patients: Frame geometry matters far more than the lens index alone!

1. Choose Small, Symmetrical Eye Sizes (Lens Width ≤ 48mm): Because minus lenses get exponentially thicker the farther you move from the optical center, cutting a lens into a small round, oval, or soft-panto frame (46-48mm eye size) automatically slices off 60% of the thickest peripheral edge! Never choose oversized aviator or wide rectangular frames for high myopia.
2. Center Your Pupils in the Frame: If your eyes sit dead-center in the frame cutout, edge thickness is distributed symmetrically. If your eyes are decentered inward toward the nose, the outer temporal edge will bulge dramatically.
3. Select 1.67 MR-7 or 1.74 Japanese Mitsui Monomers: Upgrading from standard 1.50 plastic to 1.74 reduces edge thickness by up to 50% and overall weight by 35%.

Strong minus lenses cause negative angular magnification ($M = 1 / (1 - dF)$), causing your eyes to appear 20% to 30% smaller to outside observers. To reduce minification:

• Shorten the Vertex Distance ($d$): Have your optician adjust nose pads so the lenses sit as close to your eyelashes as comfortable (e.g. 10mm instead of 14mm). The closer the lens sits to the eye, the closer the image scale returns to natural 1.0x.
• High-Index Aspheric Backside Surfacing: Flatter aspheric base curves dramatically reduce vertex bulge and edge distortion.