Although most ophthalmic medications have low systemic concentrations,
this is not true for all eye medications.  Dorzolamide (note correct
spelling) is systemically absorbed.  The ocular administration of
dorzolamide three times a day equals an oral dose of 2 mg three times a
day.
Fortunately for the breastfeeding mother, dorzolamide is 33% bound to
plasma proteins and accumulates in RBCs where it is bound to carbonic
anhydrase.  This should mean that not much of the drug enters
breastmilk.
Dorzolamide is a sulfonamide, so the mother should monitor the infant
for any possible sulfa adverse reactions.
When dorzolamide was administered to lactating rats, decreases in body
weight of 5 to 7% occurred, BUT the oral dose given to the rats was 94
times the recommended human ophthalmic dose.  Although the manufacturer
states that a decision should be made whether to discontinue nursing or
discontinue the drug, it does make the above 94 times statement and also
states that the importance of the drug to the mother should be taken
into account.
Given the above information, hopefully the mother will decide to use the
medication and continue to breastfeed.

Frank J. Nice, DPA, CPHP