How does the front vertex power of a high plus lens compare to its back vertex power?

The front vertex power of a high plus lens is less plus than its back vertex power due to the geometric characteristics of lens design. In high plus lenses, the front surface is more curved than the back surface, which leads to an increase in power at the back vertex when compared to the front vertex.

The back vertex power is calculated considering both the curvature of the lens surfaces and the distance from the front of the lens to the back, which typically includes the thickness of the lens. As a high plus lens tends to be thicker in the center, this increased thickness alters the power when measured at the back surface compared to the front.

This relationship is particularly pronounced in high plus lenses due to the significant curvature differences, often leading to a situation where the front vertex power appears less plus. Understanding this relationship is crucial for practitioners in prescribing and fitting lenses appropriately, ensuring optimal visual acuity for patients.