Stimulation of orbital growth by the use of expandable implants in the anophthalmic cat orbit

We evaluated the efficacy of expandable orbital implants to stimulate bone growth in the anophthalmic cat orbit. Eighteen cats unilaterally enucleated at 2 weeks of age received either expandable orbital implants (groups A1 and A2), solid silicone sphere implants of 12 mm or 8 mm (groups B1 and B2), or no implant (group C). Those cats with expandable implants (group A) had the implant size increased by 0.5 ml injections of saline at 2-week intervals starting at 8 weeks of age until a final volume of 4 cc was reached. Four of the expandable implants were found to be only partially inflated at 20 weeks and were subgrouped A2. At 20 weeks of age, the anophthalmic orbits with fully inflated expanders showed no significant difference in either orbital volume or orbital entrance area when compared with control orbits: volume (91.2%), area (95.7%) (p = 0.01). These same orbits also showed a significant increase in both orbital volume and orbital entrance area when compared with the growth obtained by any other group. These other groups showed growth, expressed as a percentage of normal growth, as follows: partially inflated implant: volume (63.0%), area (69.0%); 12-mm sphere implant: volume (57.0%), area (54.5%); 8-mm sphere implant: volume (46.5%), area (44.6%); no implant: volume (47.6%), area (43.6%) (p = 0.01). This study suggests that the use of expandable orbital implants stimulates bony growth in the immature cat orbit. Bony stimulation was proportional to volume implanted, and expandable orbital implants achieved maximum bony stimulation in the groups studied.