Yeah, I got that backwards. Point is that CR39 is not exactly better optically. Trivex is significantly better chromatically than PC, 1.60, ... In addition, Trivex acts as a UV cutoff filter.

What I couldn't figure out is whether a CR39 lens' comparative thickness (prism length) vs a thinner Trivex lens degrades its chromatic aberration advantage in practice.

http://eclecticeyewearaustin.com/wp-content/uploads/2016/05/...

Generally, you would expect lenses with a higher refractive index to be thinner.

However, due to the selling point of Trivex being "shatter proof" it has a greater centre thickness (to pass safety lens regulations), and thus the edge thickness is also comparable to CR-39.