Objective To identify risk factors involved in the development of idiopathic orbital inflammation (IOI).

Methods Case–control study of 69 adults who had had a first episode of IOI and 296 adult controls with rhegmatogenous retinal detachment (RD) selected from three orbital centres in The Netherlands between 2000 and 2006. Participants filled out a questionnaire on demographic factors, medical history, health status and exposures for the 2 years prior to disease presentation. In addition, women were questioned about previous or current pregnancies and their hormonal status. ORs and accompanying 95% CIs for IOI in relation to potential risk factors such as body mass index (BMI), bisphosphonates and autoimmune disease were estimated. ORs were adjusted for age, sex, socio-economic status, smoking and blunt orbital trauma using logistic regression. Analyses were carried out both with and without multiple imputation of missing values.

Results The risk of IOI was increased in participants who had a higher BMI (third vs first tertile: OR, 2.88; 95% CI 1.32 to 6.32) and in participants who used bisphosphonates (OR 8.68; 95% CI 1.16 to 65.0). The risk was decreased in participants with a higher socio-economic status (third vs first tertile: OR 0.38; 95% CI 0.17 to 0.84) and in women who were older at first childbirth (third vs first tertile: OR 0.14; 95% CI 0.03 to 0.64). An almost significant association was found for IOI and autoimmune disease (OR 2.56; 95% CI 0.93 to 7.05).

Conclusions IOI is associated with lower socio-economic status, higher BMI and use of oral bisphosphonates. In women, IOI is also associated with younger age at first childbirth.