A pupil called Worry: Mydriasis in orbital surgery

Surgeons routinely check the pupils to assess, in part, the brain stem function and the neural integrity of the visual system. Where a relative afferent pupillary defect is difficult to notice during surgery, an efferent pupillary defect or mydriasis is clearly recognizable. Visual loss in orbital surgery is attributed to compromised perfusion of the optic nerve, retina, or choroid, but an association with mydriasis is generally not assumed. This study investigates the clinical significance of mydriasis in orbital surgery to identify visual threatening situations and prevent operative complications.

PubMed search of MEDLINE and OLDMEDLINE databases, and of references in related articles, using the following Mesh and non-Mesh terms: "Mydriasis", "Pupil", "Pupillary defect", "Orbital surgery", "Visual loss", "Ciliary ganglion", "Short ciliary nerves", "Complications", and corresponding keywords of the specific lesions and surgical techniques discussed.

During an orbital procedure mydriasis regularly occurs and emerges in different shapes. The variants in mydriasis follow distinct types of injury. With surgery near the optic nerve and apex, classical circular mydriasis reflects ischemic injury involving the parasympathetic ciliary ganglion. Located deep in the orbit, the ciliary ganglion is nourished by ultrafine arteries directly or indirectly originating from the ophthalmic artery. In a varied amount of cases the ischemic event includes critical arteries for vision with resultant operative visual loss. On the other hand, oval mydriasis is related to structural injury to the short ciliary nerves. These are situated in the anterior two third of the orbit, and their injury is not associated with operative visual loss.

In orbital surgery circular mydriasis may portend visual loss whereas an oval pupil has no prognostic visual functional significance.