Frame Types, Materials, and Frame Measurements
Frame types and materials
Full-rim metal and plastic, semi-rimless with nylon cord, rimless/drill mount, and combination frames, plus hide-a-bevel, grooved, and wrap styles. Metals include monel, nickel silver, stainless steel, aluminum, titanium, and beta-titanium (light, corrosion resistant, shape memory). Plastics include cellulose acetate (zyl), optyl, and nylon. A frame is described by eye size, bridge, temple length, and vertical height.
The boxing system
A = eye size (horizontal box width), B = vertical box height, ED = effective diameter (the diagonal of the box - the smallest circle that encloses the lens shape), DBL = distance between lenses (bridge), temple length measured along the temple, and the datum line running through the box centers. Progressive fitting heights are measured from the bottom of the boxing box.
Measurement math
Horizontal decentration per lens = (A + DBL − PD) ÷ 2. Minimum blank size ≈ ED + 2 × decentration + about 2 mm of edging allowance.
Traps
- Treating the marked eye size as the lens width after the shape is changed.
- Assuming monocular PDs are exactly half the binocular PD; they are measured separately, nasal to pupil for each eye.
- Confusing DBL with a keyhole bridge's actual shape or with the nosepiece width.
Worked example
A = 52, DBL = 18, PD = 64 gives decentration = (52 + 18 − 64) / 2 = 3 mm per lens. With ED = 54 mm, minimum blank size ≈ 54 + 6 + 2 = 62 mm.