Fig. 4. A. Important anatomic landmarks on the anterior aspect of the globe. B. Schematic cross section of the limbal area at the 12 o'clock position on the globe. The corneoscleral groove (sulcus), a landmark of paramount importance, is located posterior to the termination of conjunctiva and just anterior to the termination of Tenon's capsule. A perpendicular incision (dashed line) at the corneoscleral sulcus should enter the anterior chamber just anterior to Schlemm's canal. Normally, the uvea is adherent to the anterior uvea in only one area, a narrow ring at the scleral spur. *, approximate position at which anterior ciliary vessels penetrate sclera. (Spaeth GL. Glaucoma surgery. In Spaeth GL (ed). Ophthalmic Surgery: Principles and Practice. Philadelphia: WB Saunders, 1990.)