Pubmed is filled with references to the toxicity of benzalkonium chloride to the eye. It's been well studied and well documented. This is a (probably partial) list of damage done by BAK to the eye, which I copied and pasted from a medical article:

Decreased corneal, conjunctival, trabecular meshwork, and ciliary epithelial cell survival;
Corneal epithelial cell injury;
Conjunctival goblet cell loss;
Delayed corneal wound healing;
Lymphocyte infiltration of conjunctival; epithelium and stroma;
Elevates inflammatory marker concentrations in ocular tissues;
DNA fragmentation and oxidative damage in TM cells leading to altered gene expression ;
Induction of corneal epithelial cell apoptosis .

I've attached a pdf of this specific article, however there are many supporting article. BAK is a dangerous preservative.