The cone of light, or light reflex, is a visible phenomenon which occurs upon examination of the tympanic membrane with an otoscope.[1] Shining light on the tympanic membrane causes a cone-shaped reflection of light to appear in the anterior inferior quadrant. This corresponds to the 4 o'clock to 5 o'clock position in the right eardrum and the 7 o'clock to 8 o'clock position in the left eardrum.[2] The apex of the cone is at the most depressed part of the tympanic membrane, known as the umbo.[3]
The absence of a cone of light does not necessarily signify an ear disorder, as it could be due to the slope of the tympanic membrane or the shape of the ear canal.[4] However, distortions in the cone of light can also be a sign of increased middle ear pressure or otitis media.