If the customer's pupillary distance is 60 and the finished eyewear pupillary distance is 56, what type of prism is induced?

In this situation, the customer's pupillary distance (PD) is 60 mm, while the finished eyewear PD is 56 mm. To determine the type of prism induced, it is important to understand how the difference in PD impacts the position of the optical center of the lenses in relation to the pupil.

When there is a discrepancy between the customer's PD and the eyewear PD, the optical center of the lenses will not be directly aligned with the customer's pupils if the PD is reduced in the eyewear. In this case, the finished eyewear has a narrower PD than what the customer requires.

This induced effect means that the lenses are positioned such that the optical center is closer together than the actual distance between the pupils. Since the eyewear's PD is 4 mm less than the customer's, the position of the lenses causes the light entering the lenses to appear to diverge outward from the center of the pupil. This is described as base out prism.

Inducing a base out prism occurs because the lenses are set closer together than they would naturally align with the eyes. As a result, the light being directed through these lenses will be displaced to create a visual effect as if the image is being viewed through prisms that are oriented base out.