Efficacy of hyaluronidase in reducing increases in intraocular pressure related to the use of viscoelastic substances.

OBJECTIVE: To evaluate the efficacy of hyaluronidase in preventing increases in intraocular pressure related to injections of hyaluronan-containing viscoelastic substances. METHODS: Twenty-five white rabbits were divided into 5 groups. In groups 1 through 4, 0.15 mL of aqueous humor was removed and replaced with 0.10 mL of a viscoelastic substance in both eyes. Additionally, 10 units of hyaluronidase (0.05 mL) was injected in the anterior chamber of the right eye, whereas the left eye was injected with a volumetrically equivalent dose of balanced saline solution. Viscoelastic substances tested were Healon and Healon GV (Pharmacia & Upjohn, Kalamazoo, Mich), Viscoat (Alcon Laboratories, Fort Worth, Tex), and Ocucoat (Storz Ophthalmics, Clearwater, Fla). In group 5, right eyes were injected with 10 units of hyaluronidase and the left eyes were treated with balanced saline solution. RESULTS: After injections of viscoelastic substance, intraocular pressure rose rapidly, reaching a peak at approximately 46 hours after injection and returning to preinjection levels within 24 hours. Hyaluronidase significantly decreased intraocular pressure when used with Healon, Healon GV, and Viscoat, but not with Ocucoat. When injected in the absence of viscoelastic, hyaluronidase appeared to decrease intraocular pressure, but this result was not statistically significant. CONCLUSIONS: Injections of hyaluronidase into the anterior chamber of rabbits effectively prevent increases in intraocular pressure induced by hyaluronan-containing viscoelastic substances. This effect may be related to the ability of hyaluronidase to cleave hyaluronan moieties.

Efficacy and safety of enzymatic posterior vitreous detachment by intravitreal injection of hyaluronidase.

PURPOSE: To investigate the efficacy and safety of intravitreal injection of hyaluronidase in producing liquefaction resulting in a posterior vitreous detachment. METHODS: Fifteen young pigmented rabbits were randomized into 3 groups that received 5 (group 1), 10 (group 2), or 20 (group 3) IU of hyaluronidase. The fellow eyes were injected with a volumetric equivalent dose of balanced salt solution as control. The rabbits were followed for 9 weeks and examined for signs of ocular and retinal toxicity. The animals were then euthanized and their eyes were examined histologically. RESULTS: Biomicroscopic evaluation in all but one rabbit revealed no evidence of ocular toxicity. One rabbit showed evidence of vitreous traction on the retina with transient retinal elevation. Biomicroscopically and histologically, all rabbits in group 3 and four of five rabbits in group 2 had evidence of a posterior vitreous detachment. CONCLUSION: Intravitreal injection of hyaluronidase in doses of 10 IU or higher induces posterior vitreous detachment in rabbits over a period of 5 weeks. Intravitreal doses of 20 IU or less do not appear to affect the biomicroscopic morphology or function of ocular structures adversely. Injections of hyaluronidase, therefore, could be considered as an alternative or adjunct to conventional mechanical vitrectomy.