Prism direction "in" (base in) and "out" (base out) refer to the orientation of the prism in the eyeglass lenses, used to correct horizontal eye alignment issues:

Base In: The thicker part of the prism is towards the nose. This is used to treat exotropia (when the eyes tend to drift outward) by redirecting light inward, encouraging the eyes to converge.
Base Out: The thicker part of the prism is towards the temples (away from the nose). This is used to correct esotropia (when the eyes drift inward) by shifting light outward, helping the eyes diverge.

The prism direction is tailored to each person's specific misalignment to help the eyes work together more effectively.

Eyewear Accessories

R-5A Temple Replacement Kit

Eyeglass Cords: Set of 3

M40 Mask Mount

M40 Plastic Lens Carrier

Sidestreet Temple Replacement Kit

Croakies Suiters Eggplant

Encore Temple Replacement Kit - Brown

Elite Temple Replacement Kit - Black

Encore Temple Replacement Kit - Black

Croakies Suiters Cotton Red

Croakies Woodland Cords Light Round

Delta Temple Replacement Kit

Encore Temple Replacement Kit - Pewter

Thunder Temple Replacement Kit

Elite Temple Replacement Kit - Satin Brown

Elite Temple Replacement Kit - Brushed Pewter

Croakies Woodland Cords Dark Round

Vista Temple Replacement Kit