Oculocardiac Reflex During Strabismus Surgery: Conjunctival Incision versus Standardized Rectus Muscle Traction

Background: Extraocular muscle (EOM) tension during strabismus surgery produces trigemino-vagal bradycardia as a form of the oculocardiac reflex (OCR). Surface pain in the eye can cause bradycardia in premature infant eye examinations, so we evaluated the effect on the heart rate of different aspects of strabismus surgery. Methods: Electrocardiograph heart rate (H.R.) was monitored during outpatient strabismus surgery without anticholinergic or local anesthetic. The impact of limbus-based conjunctival incision was compared to 200 gram, 10-second tension on rectus muscles. Results: The 239 patients aged 0.6 to 83 years (16± 20) during the limbal conjunctival incision had median change in H.R. from 100 bpm to 103 bpm, while initial rectus tension changed from 102 bpm to 75 bpm. Compared to median (and interquartile range) %HR with incision of 100% (100%, 101%) the corresponding first rectus tension 82% (65%, 98%) and subsequent rectus tension 80% (65%, 92%) were significantly greater (Kruskal–Wallis X2(2) = 251, p < 0.001) independent of gender, race, iris color, neurologic deficit, use of fentanyl or dexmedetomidine. Younger patients had greater percent heart rate drop with muscle tension but not conjunctival incision. Conclusion: Despite uninhibited pain receptors and general anesthesia in children and adults, conjunctival incision produced essentially no OCR compared to EOM rectus tension. Clinical Trials Registry: Clinical trial registration NCT04353960. Data Access: https://www.abcd-vision.org/references/OCR%20Incision%202025.pdf . Précis: During strabismus surgery without anticholinergic or local anesthetic, rectus muscle tension of 10-seconds and 200 grams produced a median heart rate drop of 18% however the preceding conjunctival incision elicited no change. Keywords: oculocardiac reflex, trigeminovagal reflex, bradycardia, pain, strabismus surgery