In the US, store clerks don't fit contacts or write prescriptions.

You presumably paid for a contact lens fitting. At the conclusion of a
reasonable fitting period, the doctor must give you a written copy of your
contact lens prescription. Your loophole is that you were unhappy with the
Ciba lenses and you want to try something else. If you never received a
written prescription, your position is stronger, but no good doctor wants
you wearing contacts that aren't comfortable or don't work.

The "free trial coupon" is a come-on. There's always a fitting fee (usually
just one) but the lenses aren't supposed to be charged. The only time you
_pay_ for trial lenses is when they're sold illegally in flea markets and
nail salons and tattoo parlors.

It's possible that the doctor isn't familiar with B&L lenses or has trouble
getting trials, but you've already paid for the service.

-MT, OD

In the U.S., contact lenses can only be purchased by prescription.
That prescription must specify the lens parameters, including the Brand
Name.  A prescription can only be written by an licensed eye care
professional.  A coupon is not a prescription.  If you want to try
another brand of lenses, you must go back to the person who ordered
your Ciba trial lenses and request a trial of B&Ls.

As was said, doctors who fit contact lenses have free trial lenses
available, which makes the coupon totally unnecessary.  The coupon is
just a gimmick to get you to request a specific brand of lenses.
Sometimes, the best contact lenses are manufactured by companies that
are too small to advertise.  For example, when I began having problems
with my own lenses, I came across an ad in a professional newsletter
for the Proclear lens which was manufactured by Biocompatibles, Ltd.
The rights to that lens were later purchased by Coopervision.  Going
waaay back, some of us are old enough to remember the revolutionary CSI
soft lens which was manufactured by Syntex, who also manufactured the
first mass-market RGP lens, the Polycon.  Syntex was later bought out
by Barnes-Hind, which was acquired by Pilkington.  Even the Acuvue lens
started out as the Vistamarc lens manufactured by Vistakon, which was
acquired by J&J 20 years ago.  The Acuvue polymer dates back to that
time.

DrG