Final answer:
The statement regarding the measurement of Near PD with a PD ruler being a procedure that does not require changing gaze or eyes is true. This is crucial for aligning the optical centers of lenses with the eyes' visual axis for clear and comfortable vision, akin to binocular visual processing demonstrated by the 'pen experiment'.
Step-by-step explanation:
The statement that measuring Near PD (Pupillary Distance) with a PD ruler does not require the subject to shift gaze and the dispenser does not need to change eyes during the procedure is true.
Pupillary Distance is the measurement from the center of one pupil to the center of the other. When measured for near tasks, the distance is slightly less than the PD for distance because when the eyes converge, the pupils come closer together.
In the context of optics and vision correction, near PD is vital because it ensures that the optical centers of the lenses in eyeglasses are properly aligned with the visual axis of the eyes, which is crucial for clear and comfortable vision.
This is similar to the way your brain determines the distance of objects by comparing the images from both eyes, as demonstrated by the pen experiment, where the pen's apparent shift against background objects decreases as it is held further away.
Understanding pupillary distance and proper eyeglass fitting is essential for correcting refractive errors, like those experienced by people who are nearsighted and require specific measurements for clear vision at various distances.