As with other immune disorders such as rheumatoid arthritis or Sjogren’s disease, TED typically has a progressive (active) inflammatory phase followed by a stable (inactive) post-inflammatory phase. This pattern of the disease was first described by Rundle, and the plot of orbital disease severity against time has been called Rundle’s curve. [17,18] The steepness of the graph in the active phase reflects the acuity of progression, with a steeper slope often leading to more serious sequellae. 
The duration of the active phase may last from 6 – 18 months, during which the patient may experience inflammatory symptoms of orbital discomfort, periocular and conjunctival edema (swelling) and redness, and progression in proptosis, strabismus or optic neuropathy. Management during this phase is aimed at reducing the immune response and inflammation, usually with the use of steroids, radiotherapy, or other immunosuppressive agents, and hopefully limiting the destructive consequences of the active phase.
A useful analogy is that the inflammatory phase is like a house on fire. While ignited, efforts are made to staunch the flames or allow them to smolder if not too severe. Reconstruction is not carried out while the fire is still active.