All animal-handling procedures were approved by the Allergan Animal Care and Use Committee and complied with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Fourteen Dutch-belted rabbits weighing 2 to 3 kg, with ages ranging from 3 months to 2 years, were involved in the developmental phase of the model. Before the start of the experiments, the eyes of all animals were examined externally to exclude abnormalities. Before intravitreal injections, the rabbits were anesthetized locally with topical 0.5% tetracaine HCl ophthalmic solution USP (Bausch & Lomb, Tampa, FL), and their pupils were dilated with topical 10% phenylephrine HCl (Akorn, Inc.) and 1% tropicamide USP (Alcon Laboratories, Fort Worth, TX). Twenty microliters of a hyaluronidase solution of 0.005 IU (n = 11) was intravitreally injected to induce vitreous liquefaction; another four animals received bilateral injections of 20 μL normal saline to act as the control. The animals were euthanatized 24 (n = 5) or 48 (n = 6) hours later with intravenous injection of pentobarbital (Eutha-6; Western Medical Supply Co., Arcadia, CA), and the eyes were enucleated and dissected to obtain the vitreous humor. The vitreous samples were then collected onto a Petri dish, and the gel–liquid ratio was determined by first weighing the entire vitreous and then weighing the liquid phase after removing the gel phase with a pair of forceps. The percentage of vitreous gel content was calculated as [(mass of gel phase/total mass of vitreous) × 100%]. The significance of differences in the percentage gel phase between normal and enzyme-treated eyes was evaluated by Student's t-test with the significance level defined at P < 0.05. During the study, evidence of ocular toxicity was monitored with a fundus camera.