Eyesizes

[slate83]

What determines the printed eyesize of a pair of glasses?

[LaurieC]

Well supposedly the "A" messurement for the frame but do not ever assume accuracy for the purpose of your lab measurements and just as you can try on several shoes, jackets etc of the sam esize and they're not the same so goes it. Also, if your looking to size specifically for the patient that eyesize is only the general guideline. Brisge, end piece extension etc will change it all.

[EyeManFla]

It's a top secret equation that nobody has been able to crack.

Why did we measure fronts in metric and temples in standard for as long as we did?

[Jackie L]

A PD stick and your good eye.

[chip anderson]

Acutally, It worked well.
When we measured temples in inches you could accurately estimate temple lenght to 1/4 or 1/2". You had a much more limited (in terms of variety to confuse you) selection of temple lenghts. It is a lot easier to tell the difference by sight in 4&1/2" and 5" than 135 and 147 mm. Once upon a time there were up to 17 different types and maybe a 3 inch range of temples available for a number of frame models.

Eyewires were in millimeters because the increments were smaller and metric decriminations are more suitable to small measurements than say 1/100ths of an inch.

As to eyewire sizes, the easiest way if you can't find it stamped on the frame, is remove the lens or demo and measure it with a boley gauge.

Chip:hammer:

[Wes Trayner]

The eye size and bridge size stamped on a frame are determined by the manufacturer. The "box" measurement system that we use in the United States is designed to more accurately define the measurements of a frame. If you draw a box around the frame lens opening with the top and bottom of the box paralell with the 180 line of the frame, the "A" measurement is the horizontal measurement of the box. The "B" measurement is the vertical measurement of the box. The distance between lenses (DBL or bridge) is the distance between the right and left eye boxes verticals. Another greatly mis-understood measuremnt is the effective diameter (ED). Taking the longest radius from the center of the frame and multiplying it by two is the ED. It is not the longest measurement across the frame lens opening. It is actually the smallest circle that will cut for the framelens opening.

Frames that display a small square between the eye size and the BDL are mesured on the "box"
system.