‘Ceja’ is the term for ‘eyebrow’ and we use one on each window and door.  They serve two purposes:

1. Provide a visual break to the dome's flat surface - giving texture to the outside of the dome.
   
   
2. Offer framing for the window and door installer to gain more vertical space.  When setting the doors and windows flush with the ground to top, the dome has arched inward where the door or window would vertically meet.  Thus, the ‘eyebrow’ provides the horizontal space to frame the door/window.

Making the poured concrete to support the ‘Keyhole door’ frame.

Against my better judgement, I let my crew talk me into purchasing ‘caseton’, a styrofoam block that they thought was faster and easier than making a form and pouring concrete to build the eyebrow (‘ceja’).  It makes a mess and I don't think it saved any time or money.  It was also likely imported from outside Baja.  A stupid decision, IMHO. During Hootenanny 1,  I used wood to build frames and pour a simple mix of concrete in the same time, about 2 ‘cejas’ per day.  And likely less $$.

A Window eyebrow: