<prompt> The most common cause of proptosis in adults:-Orbital cellulitisPreseptal cellulitisThyroid eye diseaseCapillary hemangioma  <response>: Most common cause of unilateral proptosis in children is orbital cellulitis and in adults is thyroid ophthalmopathy. Most common cause of bilateral proptosis in children is neuroblastoma and leukemia chloroma and in adults is thyroid ophthalmopathy. 