TY - CHAP M1 - Book, Section TI - Horner Syndrome A1 - Singh, Manpreet A1 - Whitfield, Denise A2 - Knoop, Kevin J. A2 - Stack, Lawrence B. A2 - Storrow, Alan B. A2 - Thurman, R. Jason Y1 - 2021 N1 - T2 - The Atlas of Emergency Medicine, 5e AB - Horner syndrome (miosis, ptosis, and anhidrosis) is secondary to loss of ocular sympathetic innervation. Ptosis is less than 2 mm, the result of paralysis of Müller muscle, innervated by the sympathetic pathway. Anhidrosis is often not apparent to patients or clinicians. A pupillary finding specific in Horner syndrome is dilation lag. Because the dilator muscle is weak, the pupil dilates more slowly than the normal pupil. SN - PB - McGraw-Hill CY - New York, NY Y2 - 2024/11/09 UR - accessemergencymedicine.mhmedical.com/content.aspx?aid=1181038482 ER -