What does frame PD represent in the context of eyeglass fitting?

Frame PD, or frame pupillary distance, refers specifically to the distance between the centers of the lenses in a frame, typically measured in millimeters. It is crucial in ensuring that the optical centers of the lenses are aligned with the wearer's pupils, which helps avoid visual distortions and ensures optimal vision correction.

Option B, which mentions a plus DBL (distanced between the lenses), aligns with this understanding as it involves the relationship between the frame design and the positioning of the lenses. Proper alignment of the frame PD ensures that the user experiences comfortable and effective vision through their eyewear.

The other options, such as diameter of the lens, overall frame height, and temple length, while related to different aspects of eyeglass fitting, do not pertain to the measurement of frame PD and its significance in achieving proper visual alignment.