This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of orbit, Lids and lacrimal apparatus, Subject name: Ophthalmology
Most common cause of unilateral proptosis is- 
Select and explain. 
A. Thyrotoxicosis, B. Retinoblastoma, C. Intraocular haemorrhage, D. Raised intracranial tension
A: Thyrotoxicosis
Answer: A: Thyrotoxicosis 
Explanation: *Thyroid orbitopathy is the most common cause of bilateral and unilateral proptosis. Ref: Head & Neck surgery 2nd/e p.1513