Salomon said:

just use sterile saline solution.

they sell it for contacts

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Assuming op needs eye drops because of bud smoking red eyes....saline solution will not work because the cannabis is a vasodilator, so the blood vessels in your eye are dilated and more blood flowing and can see through the sclera. 

Sooooooooo op needs a vasoconstrictive solution of which normal saline solutiom won't work. Instead try finding something with naphozaline hydrochloride or tetrahydrozoline hydrochloride. and with glycerine helps because of.the lube effects. 

Op check out visine red eye maximum redness.  Or if another country try ikul or eye kul.

Beware of overuse of drops, if you use too much your eyes will be used to the reduced eye pressure and in  short you will go through some problems probably.  Your eyes will be red unless it returns to proposed homeostasis blah blah blah

But ya good luck,hopefully I helped a bit