In this video, a 7-month-old patient presenting with primary congenital glaucoma and corneal clouding has an ab externo trabeculotomy performed on her left eye. The procedure begins with subconjunctival dissection and formation of a temporal scleral flap to locate the back wall of Schlemm’s canal (SC). A 270-degree circumferential trabeculotomy is performed with an illuminated microcatheter. The microcatheter is blocked from completing a full 360 degree pass due to scarring from a previously failed superior trabeculectomy. A scleral cutdown is used to retrieve the microcatheter. Another 40 degrees of trabecular meshwork (TM) is incised in the opposite direction using a metal trabeculotome.