What it means and why
Pupillary distance helps place the lenses horizontally relative to the eyes. A total PD combines both sides, while monocular values preserve the distance on each side of the facial reference. Faces need not be perfectly symmetrical.
Near and distance measurements are not automatically interchangeable because the eyes turn inward for near work. PD also does not locate the lenses vertically: fitting height and a correctly adjusted frame remain separate requirements.
A worked example
Teaching example: total PD 63 mm might be right 31 mm plus left 32 mm. Splitting 63 evenly gives 31.5 mm on each side, a different instruction. This illustrates lost information, not a universal tolerance or a self-measurement method.
What it does not tell you
Do not use the frame’s printed bridge width as PD. One describes the frame; the other is a wearer measurement. Accurate-looking decimal places cannot make an unsuitable measuring setup reliable.
THINK IT THROUGHDoes a total PD of 63 mm prove both monocular values are 31.5 mm?
No. Several pairs add to 63. The individual measurements are needed to distinguish them.
Sources & reading notes
Page updated:
- ABDO · Frame and lens choice ↗ Professional body guidance
Explains terminology and dispensing practice; it is not a head-to-head product trial.
- AOP · Your prescription explained ↗ Professional body guidance
Explains terminology and dispensing practice; it is not a head-to-head product trial.