The authors report a case of reversible tadpole pupil, which occurred during a routine primary uncomplicated bimedial recession in a 2½-year-old child. This case highlights a phenomenon underreported by the ophthalmic community significant in the assessment of depth of anesthesia.
From William Harvey and East Kent University Hospitals NHS Trust (REW, BPG), Ashford; and John Radcliffe Hospital Oxford University NHS Trust (SDH), Oxford, United Kingdom.
Presented at the European Vision and Eye Research Meeting (EVER) October 2–5, 2002, Alicante, Spain.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Robert E. Weir, MBBS, MRCOphth, William Harvey Hospital, Ashford, Kent, TN24 0LZ.
Received: September 21, 2009
Accepted: October 08, 2009
Posted Online: May 21, 2010
We report a case of reversible tadpole pupil, which occurred during a routine primary uncomplicated bimedial recession in a 2½-year-old child. Our findings were presented at an international research meeting where there were anecdotal reports of other cases, although none were published. We publish this case to highlight a surgically distinct, known phenomenon, which is underreported by the ophthalmic community.
A 2½-year-old boy presented to our clinic with a 40-diopter squint and cross fixation, which was undiminished by refractive correction. He had no medical or ophthalmological history. He underwent routine bimedial rectus recession of moderate esotropia by an experienced strabismus surgeon (BPG).
Normal inhalational anesthesia was used without opiate analgesics. No pupillary dilating drops were used preoperatively, perioperatively, or postoperatively. Topical anesthetic drops without adrenaline and chloramphenicol were applied to the muscle before conjunctival closure over each muscle. No visible hemorrhage occurred with normal scleral reattachment of the muscles during the procedure. A standard amount of bipolar diathermy was used to achieve hemostasis.
The left medial rectus muscle was recessed by 7.5 mm and reattached to the sclera with 6.0 polyglactin 910 absorbable sutures, and the conjunctiva was closed with buried 8.0 polyglactin 910 absorbable sutures. A few minutes after the conjunctiva closure, during regular hydration of the corneas with balanced salt solution, the operating assistant noted that the left pupil had dilated in a tadpole shape at the 7-o’clock position (Figure). The focal tadpole-shaped dilation had spontaneously resolved entirely at the postoperative ward round approximately 45 minutes later. The right pupil remained normal during right medial rectus recession surgery. The child made a routine recovery achieving an excellent postoperative squint alignment without reoccurrence.
Figure. Tadpole Pupil Orientated Towards Left, Inferior Medial Rectus Suture Placement.
Non-tadpole pupil dilation occurs with muscle manipulation in more than 70% of strabismus surgeries in children receiving inhalation without intravenous anesthesia.1 Pupil dilation is important during strabismus surgery for both anesthetist and surgeon to assess the depth of anesthesia and adequacy of oxygenation. When anesthesia depth is steady, pupil diameter is small as the sympathetic activity is depressed. However, variations in perioperative pupil diameter2 occur with strabismus surgery unrelated to anesthesia.3,4 A review of the literature describes this pupillary dilatation, measured horizontally, occurring during strabismus surgery independent of the number or type of extraocular muscles operated on.3 Pupil contraction was also described in two of these 19 cases.
Horizontal pupil diameter assessments cannot properly assess the more unusual tadpole pupil dilation reported here. Release of chemical messenger from traumatized tissue, surgical ischemia of the iris, and Tournay’s phenomenon associated with lateral gaze have all been suggested as possible mechanisms for pupil dilation,3 although these remain controversial. Tractional damage to the parasympathetic fibers was attributed specifically to a series of inferior oblique myomectomies with longterm persistent pupil anisocoria.4 This tadpole-shaped dilation suggests localized mechanisms of sympathetic nerve stimulation occurring well in excess of any physiological asymmetry. The tadpole peak was orientated toward the inferior placed suture (Figure).
This transient localized effect suggests a non-systemic mechanism that occurred with medial rectus reattachment. Tadpole pupil is a physical description of a variation in shape of the pupil. The focal widening of the pupil in one meridian leads to a tail appearance developing (Figure). Episodic tadpole pupil dilation has been described as early as 1912.4 Sporadic episodes of tadpole pupil appearance have been reported to occur in an older age group associated with Horner’s syndrome,5,6 Adie’s pupil, and migraine.6 The Tadpole pupil shape most likely results from a generalized maintenance of pupil sphincter tone with a simultaneous focal contraction of isolated sympathetic innervated pupil dilator muscles. This is possibly analogous to the hemi-facial spasm findings that occur in facial nerve irritation.
We believe that tadpole pupil associated with strabismus surgery is underreported. The authors are unaware of any long-term consequences. The occurrence with reattachment and the pupil morphology distinguishes this clinical entity of pupil dilation related to strabismus surgery.1,4 Tadpole pupil during strabismus correction causes significant change to the pupil anesthesia depth assessment in the unilaterally exposed affected eye, requiring examination of the fellow pupil, which may also be unreliable.1,3
- Venemans EF, de Keizer RJ, Swart-van den Berg M, Baartse WJ. Reversible mydriasis during strabismus surgery in children. Doc Ophthalmol. 1993;83:65–70. doi:10.1007/BF01203571 [CrossRef]
- Asbury AJ, Lear GA, Wortley D. Pupillometer for use during anaesthesia. Anaesthesia. 1984;39:908–910. doi:10.1111/j.1365-2044.1984.tb06581.x [CrossRef]
- James CB, Elston JS. Effect of squint surgery on pupillary diameter. Br J Ophthalmol. 1995;79:991–992. doi:10.1136/bjo.79.11.991 [CrossRef]
- Bajart AM, Robb RM. Internal ophthalmoplegia following inferior oblique myectomy: a report of three cases. Ophthalmology. 1979;86:1401–1406.
- Balaggan KS, Hugkulstone CE, Bremner FD. Episodic segmental iris dilator muscle spasm: the tadpole-shaped pupil. Arch Ophthalmol. 2003;121:744–745. doi:10.1001/archopht.121.5.744 [CrossRef]
- Thompson HS, Zackon DH, Czarnecki JS. Tadpole-shaped pupils caused by segmental spasm of the iris dilator muscle. Am J Ophthalmol. 1983;96:467–477.