Hi,
Methafilcon is an ultra high molecular weight copolymer of
2-Hydroxyethyl methacrylic and methacrylic acid (MMA). Methafilcon is
an ionic polymer with a 55% water content that does not yellow after
repeated disinfection cycles. The
polymerization process ensures a material that results in a lens with
good dimensional stability.
http://www.benzrd.com/englishmanual.pdf
The first member of a series is assigned a unique nonproprietary name
containing the proper -filcon or -focon suffix stem.
A separate capital letter "A" is added after each parent designation.
Subsequent designations for polymers consisting of identical monomers
receive the same parent name but a different appended letter (B,C,D,
etc).
These letters are needed to differentiate between polymers of
identical monomeric units but with different ratios of units that have
different physiochemical properties, as determined by water content,
oxygen permeability [Dk] value, specific gravity, refractive index,
surface charge, wetting angle, elasticity, and toughness of the lens.
http://www.ama-assn.org/ama/pub/category/4853.html
So in other words, Methafilcon A was the first one produced. Then they
changed something slightly so they had to leave the name the same and
assign a new letter resulting in Methafilcon B.
Perhaps another researcher will have more success with finding out
what exactly thay changed. The only thing I can find is that in most
cases A does not need to be fitted and B does, but that is not always
the case.
Good question. Hope someone digs up the answer.
bcguide-ga
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