An explanation of adjustment workflow:
https://youtu.be/GaLWMHGap_k
The adjustment morph targets are the following:
width.Exclusive, forward.Exclusive, up.Exclusive - positioning of front part of the glasses ("width" being distance between eyes);
width_ears.Exclusive,forward_ears.Exclusive,up_ears.Exclusive - positioning of ear hooks;
noseWidth.Exclusive - width of nose part;
scale_lenses.Exclusive - size of the lenses;n
thickness.Exclusive - frame thickness;
scaleX.Exclusive,scaleY.Exclusive,scaleZ.Exclusive - scale entire mesh using head bone as origin. Used to compensate for non-uniform scaling of certain heads.
The "width" shape key is best used in conjunction with lens scale and nose width keys.
Examples of *.xpf preset files:
https://github.com/DimitriX89/IMVU-community-R-D/blob/master/Projects/glasses_female_default.xpf
https://github.com/DimitriX89/IMVU-community-R-D/blob/master/Projects/glasses_female_smaller.xpf
https://github.com/DimitriX89/IMVU-community-R-D/blob/master/Projects/glasses_male_bigger.xpf
https://github.com/DimitriX89/IMVU-community-R-D/blob/master/Projects/glasses_male_default.xpf
https://github.com/DimitriX89/IMVU-community-R-D/blob/master/Projects/glasses_male_pid4509975.xpf
The "pid4509975" is an example of a preset for specific head (with non-uniform scaling)