Description: OBJECTIVE To compare the efficacy of various concentrations and combinations of serum, EDTA, 3 tetracyclines, and N-acetylcysteine (NAC) for collagenase inhibition in an in vitro corneal degradation model. SAMPLE Grossly normal corneas from recently euthanized dogs and horses and fresh serum from healthy dogs and horses. PROCEDURES Serum was pooled by species for in vitro use. For each species, sections of cornea were dried, weighed, and incubated with clostridial collagenase (800 U/mL) in 5 mL of a 5mM calcium chloride-saline (0.9 PROCENT NaCI) incubation solution and 500 pL of I of 19 treatments (homologous serum; 0.3 PROCENT, 1.0 PROCENT, or 2 PROCENT EDTA; 0.1 PROCENT, 0.5 PROCENT, or 1.0 PROCENT tetracycline, doxycycline, or minocycline; 0.5 PROCENT, 1.0 PROCENT, or 5.0 PROCENT NAC; serum with 0.5 PROCENT tetracycline; serum with 1.0 PROCENT EDTA; or 1.0 PROCENT EDTA with 0.5 PROCENT tetracycline). Positive and negative control specimens were incubated with 5 mL of incubation solution with and without collagenase, respectively. Each control and treatment was replicated 4 times for each species. Following incubation, corneal specimens were dried and reweighed. The percentage corneal degradation was calculated and compared among treatments within each species.RESULTS Treatments with tetracyclines at concentrations =0.5 PROCENT, with EDTA at concentrations = 0.3 PROCENT, and with NAC at concentrations = 0.5 PROCENT were more effective at preventing corneal degradation than serum in both species. The efficacy of each combination treatment was equal to or less than that of its components. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested EDTA, tetracyclines, and NAC may be beneficial for topical treatment of keratomalacia, but in vivo studies are required.