Although transillumination is not part of a routine examination, it is often helpful when sinus tenderness or other symptoms suggest sinusitis. The room should be thoroughly darkened. Using a strong, narrow light source, place the light snugly deep under each brow, close to the nose. Shield the light with your hand. Look for a dim red glow as light is transmittted through the air-filled frontal sinus to the forehead. Absence of glow on one or both sides suggests a thickened mucosa or secretions in the frontal sinus, but it may also result from developmental absence of one or both sinuses.