The Oculocardiac Reflex in Identical Twins

To the Editor.  —The oculocardiac reflex (OCR) is a slowing of the heart rate due to ocular manipulation and particularly tension on the extraocular muscles. The response is variable from one patient to the next and rarely produces profound bradycardia.¹ Only ten of 77 patients with strabismus who had not received a vagolytic drug had heart rate reductions greater than 40%, and only two of 77 had reductions greater than 50%.² Anesthesiologists have concentrated primarily on methods of reducing the prevalence of OCR, such as intravenous anticholinergic medications or retrobulbar local anesthesia.³ There has been minimal effort to determine means of predicting the OCR.⁴ In fact, it is not known whether a given patient has a repeatable tendency toward low heart rates with ocular manipulation.⁵Two healthy 4-year-old female identical twins underwent strabismus surgery for V pattern esotropia. Each had general endotracheal anesthesia with fentanyl