Question

Measuring Near PD with a PD ruler:

Dispenser is positioned at the subjects working distance, closing his or her poorer eye, the dispenser aligns his or her better eye directly before the subjects nose and instructs the subject to look into the open eye. The PD ruler is lined up with ____ point corresponding to the center of the subjects right pupil.

Answer 1

When measuring Near PD with a PD ruler, the dispenser aligns the ruler's zero point with the center of the subject's right pupil. This ensures proper alignment of spectacle lenses for clear vision at near work distances, taking into account factors like the individual's near point and the accommodation process of the eye.

Step-by-step explanation:

When measuring Near PD (Pupillary Distance) with a PD ruler, the dispenser aligns the ruler with the zero point corresponding to the center of the subject's right pupil.

This measurement is important for ensuring that spectacle lenses are properly aligned with the patient's line of sight to aid in clear vision, particularly at near work distances.

For clear vision, the image must be on the retina, and factors such as the individual's near point, the distance from lens to retina, and the process of accommodation come into play. If a person has a near point of 25 cm, spectacle lenses or contact lenses need to produce an image at this distance, even if the physical object is closer.

Answer 2

The zero point on the PD ruler should align with the center of the subject's right pupil to accurately measure Pupillary Distance.

Step-by-step explanation:

When measuring Near PD (Pupillary Distance) with a PD ruler, the PD ruler should be lined up with the zero point corresponding to the center of the subject's right pupil. This ensures that the measurements taken for corrective lenses, such as glasses or contact lenses, are accurate to provide clear vision. For clear vision, the image must fall precisely on the retina, which is accomplished by the eye's lens adjusting its power (accommodation) for objects at various distances. A person with normal vision has a near point of approximately 25 cm, whereas this distance can increase with age.

To measure the near PD (pupillary distance) with a PD ruler, the dispenser positions themselves at the subject's working distance, closes the subject's poorer eye, and aligns their better eye directly before the subject's nose. The dispenser then instructs the subject to look into the open eye. The PD ruler is lined up with a point corresponding to the center of the subject's right pupil.