best-form spheric vs aspheric

I was told by my optician that there would always be a slight benefit
to aspheric lenses. However, my research seems to indicate that a
true best-form spheric is best. My question is, If someone has a
prescription filled with a CR-39 lens, would they automatically be
getting a best-form spheric? If not, how can a person make sure they
are getting a best-form spheric?

 

The real question is: Best for what? Lens design is always a trade-off. That
applies even for simple lenses. For example, how much do you value best
resolution looking straight ahead along the axis of your lens compared to
facing straight ahead and pivoting your eyes to see in and off-axis
direction?

Lens designers use some kind of merit function that is a weighted average of
all kinds of performances. Such a merit function is often subjective. With
that merit function, a lens can be designed to maximize it under whatever
fabrication constraints there may be. It is like asking what combination of
spices will give the best taste to chili.

Fortunately, it is usually not necessary to go to such extremes.

Bill
-- Fermez le Bush--about two years to go.

 

The reason I ask is that my mother has macular degeneration. She can
still see to carry out daily activities, but she is starting to lose
central vision. I am trying to determine what type of lens will give
her the widest field of clear vision.