I believe that the reference to `optically-scaled' refers to the phenomenon
that, for most people, linear-scaled scaled fonts at small sizes seem less
bold than the larger sizes.  An optically-scaled fonts would be scaled
bolder at small sizes so that, subjectively, the fonts would seem to be
of the same weight.

Randolph J. Herber, [log in to unmask], +1 630 840 2966,
CD/OSS/CDF CDF-PK-149O Mail Stop 318
Fermilab, Kirk & Pine Rds., P.O. Box 500, Batavia, IL 60190-0500.
(Speaking for myself and not for US, US DOE, FNAL nor URA.)
(Product, trade, or service marks herein belong to their respective owners.)
N 41 50 26.3 W 88 14 54.4 and altitude 700' approximately, WGS84 datum.