['To determine the impact of enucleation with hydroxyapatite implant on bony orbital development in survivors of retinoblastoma (RB) by measuring orbital volume based on CT imaging.', 'The authors used CT images obtained at a median age of 6 years to measure orbital volume of RB and contralateral orbits in 18 patients who underwent enucleation with hydroxyapatite implant for RB. Comparison of the orbital volume of RB and contralateral orbits was done using the Wilcoxon rank sum test.', 'The mean age at diagnosis and operation was 29±23 months, and the mean follow-up was 49±31 months. The mean volume difference between RB and contralateral orbits was 0.93±1.13 cm(3). RB orbits with hydroxyapatite implant were statistically significantly smaller than contralateral orbits (p=0.002). The age at operation was significantly negatively correlated with orbital volume difference (p=0.033). Orbital volume differences for children treated by enucleation before the age of 12 months were also statistically significantly larger than those treated later. (p=0.03).'] Do orbital development in survivors of retinoblastoma treated by enucleation with hydroxyapatite implant?