Location of the Ciliary Ganglion within the Orbit
Authors: Hamdan Marah , Balsiger Heather , Gest Thomas 
Published: April 2020

The ciliary ganglion (CG) is a parasympathetic ganglion located in the orbit that controls pupil contraction, accommodation, ocular blood flow, intraocular pressure, and aqueous humor production. Micro and macro‐surgical lesions to the CG can affect nearby structures and lead to Adie’s Tonic Pupil or Argyll Robertson Pupil. This study was performed to better understand the CG location within the orbit. Few studies have analyzed the distance from the CG to neighboring structures with evident variation in the mean distance between the posterior globe (PG) and the CG, which can prove clinically significant in orbital floor surgical procedures. Besides direct clinical impact, this research would be beneficial in medical education by enabling a more accurate depiction of the CG in anatomical illustrations. Lastly, this is a novel study in that it measures the distance in relation to a relatively immobile structure, rather than to a more dynamic and variable neural or vascular structure.MethodsNine cadaver heads were bisected for a total of 18 samples, and two additional bisected half heads were used. The calvaria, brain, cranial fossa dura matter, frontal bone, and lesser wing of sphenoid bone were removed. Once orbital contents were visualized, dissection began by identifying the anterior and posterior ethmoidal nerves that run superior to the upper border of the medial rectus muscle. Blunt dissection was used to trace them back to the nasociliary nerve, an ophthalmic nerve division. The nasociliary nerve sends a sensory root to the CG. The oculomotor nerve (CN III) passes through the common tendinous ring, which was dissected open to allow better visualization of CN III inferior and superior divisions. The inferior division of CN III, which carries parasympathetic contribution to the CG, was dissected. The CG was confirmed by tracing the sensory nasociliary branch and the parasympathetic root from the inferior division of CN III to CG. Once identified, the CG was pinned in the center, in its natural position. The distance from the PG at the optic nerve juncture and the pinned CG was measured three separate times, removing and placing the pin in the center for each measurement. The three measurements average was used. The second measurement was from the posterior clinoid process (PCP) to the pinned ganglion, measured three separate times, and the average was used for each ganglion.ResultsThe average distance range between PG and CG was 8.95 – 24.63 mm, with the average of the 20 mean measurements being 17.853 mm. The average distance range between CG and PCP was 28.23 – 39.58 mm, with the average of the 20 mean measurements being 35.135 mm.ConclusionThe distance from the PG to the CG center was 17.85 mm, and from CG center to PCP was 35.135 mm. This varies from other studies that have reported the distance between the PG and CG to be 12 mm, 2–3 mm, and 15–20 mm. The CG is 2.9 mm lateral to the optic nerve and could be damaged during lateral orbiotomy procedures. In terms of anatomical education, illustrations in Netter and Gray’s differ in the location of the CG. These results support Gray’s proposition that the CG is further posterior relative to the posterior globe rather than being closer to the globe as shown in Netter’s atlas. Ours is a novel study to clarify the position of the CG within the orbit.