What could affect the accuracy of the PD measurement?

The accuracy of the pupillary distance (PD) measurement can be significantly influenced by the proposed working distance. Working distance refers to the distance from the lenses to the patient's eyes when they are wearing glasses. If the working distance is not properly considered, it can lead to misalignment of the optical centers of the lenses with the patient’s pupils, especially in single vision and multifocal lenses. This misalignment can lead to visual discomfort or reduced visual acuity.

If the working distance is too close or too far when taking the measurement, the PD obtained may not correspond to the glasses' actual use. Therefore, correctly measuring PD at the appropriate working distance is crucial for ensuring that prescription lenses will perform optimally in their intended setting.