When should a change in the base curve of a lens be considered?

A change in the base curve of a lens should be considered primarily when there is a significant difference in the new prescription compared to the old one. This is because a new prescription that alters the refractive error may impact the fit and effectiveness of the lenses. The base curve of a lens is crucial for proper centration and alignment with the wearer’s eyes, and a significant change in prescription may require an adjustment in base curve to ensure optimal visual performance and comfort.

When a new prescription differs significantly, it could necessitate a different lens design or curvature to provide the best possible vision. The base curve affects how light is refracted through the lens, and without adjusting it appropriately, the wearer may experience issues such as distortion or discomfort.

Considering the other scenarios: a scratched lens may require replacement of the lens itself, but it does not necessarily need a change in base curve. A broken frame would warrant repairs or replacement without directly involving the base curve unless the lens also needs to be reassessed due to the change in fit. Finally, while dirty lenses require cleaning but not a change in base curve, as the lens curvature still remains the same regardless of surface cleanliness. Thus, option C stands out as the valid condition for considering a change in base curve