What's the difference between naphcon and naphcon-a eye drops?

Anti-allergic: Both drops contain a mild vasoconstrictor (naphazolamine) which can help whiten up allergically affected eyes. Naphcon-a, an alcon company brand name, also contains pheneramine, which is a mild anti-histamine. So plain naphcon can briefly eliminate the redness but does not treat anything while naphcon a can decrease the redness but also treat the allergy.