The influence of hyperbaric oxygen therapy and irradiation on hydroxyapatite ocular implant exposure and fibrovascular ingrowth in New Zealand white rabbits

Purpose: Lack of adequate fibrovascular ingrowth has been implicated as a c ause of exposure of hydroxyapatite (HA) implants in anophthalmic sockets. W e investigated the vasculopathic effects of external beam irradiation, and the fibrovascular-enhancement effects of hyperbaric oxygen (HBO), on HA imp lant exposure and fibrovascular ingrowth in a rabbit model. Methods: Eighteen rabbits underwent enucleation with implantation of a 12-m m HA sphere. Six rabbits received 20 Gy of external beam orbital irradiatio n prior to enucleation. Three irradiated and 6 nonirradiated rabbits receiv ed postoperative HBO. Three weeks postoperatively, all rabbits were evaluat ed clinically for evidence of implant exposure. Implants were then removed, and histopathologic analysis of fibrovascular ingrowth was performed. Results: The amount of vascularization as measured by the depth of ingrowth was greater for nonirradiated (89% ingrowth) than for irradiated (71% ingr owth) animals. HA implant exposure occurred in 1 of 12 (8%) of the nonirrad iated, and 4 of 6 (67%) of the irradiated rabbit orbits. HBO did not protec t irradiated rabbits from exposure, but did enhance fibrovascular ingrowth in nonirradiated rabbits (100% ingrowth vs. 77% ingrowth). Conclusion: Impaired orbital vascularization from prior irradiation appears to retard fibrovascular ingrowth into HA implants, and is associated with an increased incidence of exposure. While HBO did not diminish the likeliho od of exposure in irradiated sockets, HA fibrovascular ingrowth in normal o rbits appeared to increase with HBO. This may have beneficial clinical appl ication in cases of exposure in nonirradiated orbits.