The effect of maturation on the ability to stimulate orbital growth using tissue expanders in the anophthalmic cat orbit

Tissue expanders were used to stimulate orbital growth at different stages of maturity in the immature anophthalmic cat orbit. Twelve cats had the right globe enucleated at 2 weeks of age and tissue expanders implanted in the orbit. The cats were randomized into four groups (A, B, C, and D). The tissue expanders remained in the nonexpanded state for a preassigned length of time. Orbital volume was determined on each cat using computed tomography (CT) immediately prior to expansion of the implant. Expansion began at age 10 weeks for group A, 15 weeks for group B, and 25 weeks for group C and involved 0.7 cc injections of saline at 2-week intervals until a final volume of 4.5 cc was obtained. Group D remained as a nonexpansion control group. Four to 5 weeks after expansion was completed, a second orbital volume CT was obtained on each animal and compared with the pre-expansion CT. The right orbits of group A, had pre-expansion (week 10) orbital hypoplasia with a volume 26.2% smaller than the left control orbits. Postexpansion (week 25), the right orbital hypoplasia had decreased to a volume 10.3% less than the left control orbits. The right orbits of group B had pre-expansion (week 15) orbital hypoplasia with a volume 35.6% smaller than the left control orbits. Postexpansion (week 31), the right orbital hypoplasia had decreased to a volume 25.9% less than the left control orbits. The right orbits of group C had a preexpansion (week 25) orbital hypoplasia with a volume 39.8% smaller than the left control orbits. Postexpansion (week 41), the right orbital hypoplasia had decreased to a volume 29.3% less than the left control orbit. Tissue expanders, expanded in the hypoplastic immature cat orbit stimulated orbital growth and reversed orbital bony hypoplasia to varying degrees. The amount of growth stimulated was inversely proportional to the age at which expansion began. Orbital growth, stimulated by tissue expander expansion, was also demonstrated after the normal age of cat orbit maturation (weeks 28-30).