prepared by methods that are known in the art or according to the working examples below the compounds below are especially preferred representative of the compounds of the present invention a pharmaceutically acceptable salt is any salt which retains the activity of the parent compound and does not impart any deleterious or undesirable effect on the subject to whom it is administered and in the context in which it is administered of particular interest are salts formed with inorganic ions such as sodium potassium calcium magnesium and zinc pharmaceutical compositions may be prepared by combining a therapeutically effective amount of at least one compound according to the present invention or a pharmaceutically acceptable acid addition salt thereof as an active ingredient with conventional ophthalmically acceptable pharmaceutical excipients and by preparation of unit dosage forms suitable for topical ocular use the therapeutically efficient amount typically is between about 0 0001 and about 5 w v preferably about 0 001 to about 1 0 w v in liquid formulations for ophthalmic application preferably solutions are prepared using a physiological saline solution as a major vehicle the ph of such ophthalmic solutions should preferably be maintained between 6 5 and 7 2 with an appropriate buffer system the formulations may also contain conventional pharmaceutically acceptable preservatives stabilizers and surfactants preferred preservatives that may be used in the pharmaceutical compositions of the present invention include but are not limited to benzalkonium chloride chlorobutanol thimerosal phenylmercuric acetate and phenylmercuric nitrate a preferred surfactant is for example tween 80 likewise various preferred vehicles may be used in the ophthalmic preparations of the present invention.