At what point does lens thickness affect lens power?

Lens thickness affects lens power primarily when it is considered in conjunction with curvature. The power of a lens is determined significantly by its shape, which is defined by the curvature of its surfaces, and this is often affected by the thickness of the lens as well.

When a lens is thick, the way light is refracted can change depending on both the curvature and the thickness. Specifically, as thickness increases, it can introduce additional optical effects such as increased spherical aberration and changes in effective focal length. These factors become especially relevant in thicker lenses, where simple curvature alone may not accurately predict how the lens will perform.

The other choices do not capture the relationship between lens thickness and power as comprehensively. While thickness can influence power in general, it is the interaction with curvature that truly dictates the net effect on lens power.