The study was a randomized, double-masked clinical trials planned to include 1,200 infants born over 3 years. The trial compared the efficacy of two treatment regimens (silver nitrate and erythromycin) in two treatment groups to the outcomes in a control group receiving no prophylaxis. (Erythromycin was chosen over tetracycline as the antibiotic in this study because it is more commonly used in the United States for ocular prophylaxis.)