Transillumination is used in the evaluation of the maxillary and frontal sinus.

Maxillary Sinus	Dim the light in the room. Place a flashlight / otoscope on maxillary sinus. Examine the hard palate from the patient's open mouth and look for an orange glow.
Frontal Sinus	Dim the light in the room. Place a flashlight / otoscope under each eyebrow pointed upwards. Cover the light source with your hands to shield the light from your eyes. Look for an orange glow over the frontal sinus.

A decrease in the amount of light passing through the sinus indicates that fluid has filled the sinuses and indicates a possible sinusitis.

NOTE: transillumination is not a very good diagnostic tool. It requires an expert examiner and cannot differentiate a viral vs bacterial sinusitis. Therefore, this is not a recommended diagnostic test.