A comparison of rates of fibrovascular ingrowth in wrapped versus unwrapped hydroxyapatite spheres in a rabbit model

Purpose: To compare the rate of fibrovascularization of wrapped versus unwrapped hydroxyapatite (HA) spheres in an animal model and to investigate how drilling small-diameter access holes at the time of implantation affects the rate of fibrovascular ingrowth in wrapped implants. Methods: The right eyes of 20 New Zealand White rabbits were removed and a 12-mm HA sphere was implanted in each socket. The spheres were left bare in 8 of the animals. In the other 12, the implant was wrapped in an autologous sclera shell. In 4 animals from each group, a 1-mm diameter access hole was drilled into the spherical center of the implant at the sites of extraocular muscle insertion and at the posterior pole before implantation. All implants were explanted after 1 week. Results: The mean depth of fibrovascularization in the bare group without access holes (n=4) was 100% (SD=0). The mean depth of fibrovascularization in the wrapped group without access holes (n=8) was 30.1% (SD=11.0). The difference between these two groups was statistically significant (P<0.001). The mean depth of fibrovascularization in the wrapped group with access holes (n=4) was 91.5% (SD=9.8). Compared with the wrapped group without access holes, the difference was statistically significant (P<0.001). The difference in the mean depth of fibrovascularization between the bare group without access holes and the wrapped group with access holes failed to reach statistical significance (P=0.18). Conclusions: On the basis of this preliminary study, we conclude that whereas scleral wrapping does significantly slow the rate of fibrovascular ingrowth, the concomitant placement of access holes greatly improves the rate of fibrovascularization.