Author Block: Charlotte Lussier ¹, Victoria C. Leung², Jessica El-Khazen Dupuis¹, Davin C. Ashraf³, Oluwatobi O. Idowu³, Erika Massicotte¹, Reza M. Vagefi³, Robert C. Kersten³, Evan Kalin-Hajdu¹.  ¹Université de Montréal, ²William Osler Health System, ³University of California, San Francisco.

Author Disclosure Block:   C. Lussier:  None.  V.C. Leung:  None.  J. El-Khazen Dupuis:  None.  D.C. Ashraf:  None.  O.O. Idowu:  None.  E. Massicotte:  None.  R.M. Vagefi:  None.  R.C. Kersten:  None.  E. Kalin-Hajdu:  None.

Abstract Title: "Prevalence and predictors of Hering’s response in Müller’s muscle-conjunctival resection"

Abstract Body: Purpose:  "Determine the prevalence and predictors of Hering’s response following Muller's Muscle-Conjunctival Resection (MMCR)."  Study Design:  "Seventy-five consecutive patients undergoing unilateral MMCR were recruited in this prospective, multicenter, cohort study."  Methods:  "Margin-reflex distance-1 (MRD1) of both eyelids was recorded preoperatively and postoperatively. One hundred forty-five variables were investigated as potential predictors of a late postoperative (≥3 months) Hering’s response using regression analyses.   Main outcome measures were Hering’s response (≥0.5 mm descent of the unoperated eyelid from baseline), and a clinically relevant Hering’s response (descent of the unoperated from baseline to a MRD1 2.0 mm, or descent from baseline such that the MRD1 of the unoperated eyelid became >1 mm lower than the operated eyelid)."  Results:  "Twenty-four (32.0%) patients had a late postoperative Hering’s response, but only 6 (8.0%) responses were clinically relevant. A Hering’s response at the immediate (OR 16.24, p=0.02) and 1-week postoperative (OR 8.94, p=0.04) timepoints predicted a late postoperative response. However, the presence (OR 7.84, p=0.07) and amplitude (OR 8.13, p=0.06) of a preoperative phenylephrine Hering’s response did not predict a late postoperative response. Of the 10 patients with a clinically relevant phenylephrine Hering’s response, only 1 demonstrated a clinically relevant response late postoperatively."  Conclusions:  "Unilateral MMCR induces a clinically relevant Hering’s response in 8% of patients. A preoperative phenylephrine Hering’s response does not predict a late postoperative Hering’s response. Therefore, when unilateral phenylephrine testing unmasks contralateral blepharoptosis, only the side with blepharoptosis at baseline should be operated."