Thyroid eye disease is probably the most common clinical case in this section. Most patients in this section will have proptosis as the main feature and thyroid eye disease is the most likely diagnosis in both unilateral or bilateral cases. Nonetheless, you must always remember to consider other possibilities and the mnemonic VEIN is useful
 

• Vascular causes such as cavernous haemangioma and carotid-cavernous fistula,
• Endocrine cause as in thyroid eye disease,
• Inflammatory and Infection such as pseudotumour and orbital cellulitis and
• Neoplasm such as optic glioma, meningioma and orbital lymphom.