Hyaluronic Acid Gel Biodegradation After Intrapalpebral and Intraorbital Injection in Experimental Study

Amid the increasing clinical application of hyaluronic acid (HA) fillers in the ocular adnexa is a paucity of histological data concerning the fate of the injected material. The current study documents the in vivo biodegradation of HA deposited in the eyelid and orbit.The study included 22 chinchilla rabbits. The right upper eyelid of 12 rabbits received a single 0.2 ml Restylane (Galderma, Uppsala, Sweden) subcutaneous injection. In 10 different rabbits, the right orbit was injected with 1.0 ml Restylane SubQ (Galderma, Uppsala, Sweden) in the extraconal space. The rabbits in the eyelid group were euthanized at 2 weeks, 1 month, 2, 4, 6, and 9 months, while the rabbits in the orbit group were euthanized at 1 month, 3, 6, 12, and 18 months. Histological analysis was performed on the harvested samples.In the eyelid, the HA assumed a sponge-like structure that diminished gradually over time. At 9 months, the injected HA partially persisted, mainly in the peripheral areas of injection. A similar histologic pattern was observed in the injected orbits, with slow changes persisting at the eighteenth month. In both cohorts, clear signs of collagen deposition and pseudocapsule formation were observed around HA droplets, with no signs inflammation.HA injected subcutaneously into the eyelid and orbit of rabbits undergoes slow and gradual biodegradation, with HA persisting to no less than 9 months in the eyelid and 18 months in orbit. Neocollagen synthesis and lack of hyaluronidase activity could explain the unexpectedly prolonged HA persistence.