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To analyze orbital morphological parameters that potentially could influence the effect of decompression surgery on exophthalmos reduction in Graves orbitopathy, thus making decompression surgery more predictable.To generate a reference database, a CT-based study was performed in 140 orbits obtained from adult patients with unaffected orbits in a European white ethnicity. The following parameters were chosen: orbital volume, globe volume, globe to orbital volume ratio, and orbital cone angle. Volumes were measured on postprocessed CT data using morphometric techniques. To define the cone angle, a 3-dimensional approach was chosen using the program Amira.Significant interindividual variation was found in orbital volume from 18.9 to 33.4 ml and in globe volume from 6.0 to 10.1 ml. The globe to orbital volume ratio showed a relatively broad variation from 0.25 to 0.4. Differences in the orbital cone angle from 39.7° to 65.7° were observed.The experienced large variations in orbital morphology might significantly influence the degree of exophthalmos reduction, which can be obtained by standardized decompression procedures. Based on our results, a prospective clinical study will be conducted to test our hypothesis.