Anatomy of the limbus (view from above).

(a) Limbus prior to the conjunctival dissection

(b) Limbus following the conjunctival dissection. In the drawing, it is outlined by red markings.

The surgical limbus is the blue-gray area lying between the sclera and the clear cornea (outlined by red markings); it can be identified following the removal of the conjunctiva and the Tenon’s capsule (b). Its posterior margin normally overlaps the anterior portion of the sclero-corneal trabecular meshwork. Schematically we can identify the following structures, from anterior to posterior: the anterior margin of the limbus, consisting of the Schwalbe line, the posterior boundary consisting of the scleral spur, and finally the trabecular meshwork that lies between these two structures. The conjunctiva and the Tenon’s capsule are inserted into the cornea at the Bowman membrane, and cover the limbus. In most anti-glaucomatous surgeries (particularly if they are penetrating), the conjunctiva and the Tenon’s capsule must be respected and handled with care: the integrity of these structures makes an important contribution to the surgical outcome. The Tenon’s capsule is firmly adhered to both the conjunctiva above and the episclera below, along a line that extends for approximately 1 mm posteriorly to the sclero-corneal junction. Because of this anatomical relationship during the preparation of a fornix based flap it is possible to dissect the conjunctiva and the capsule together, as though the two structures formed a single layer, starting the incision in correspondence with the external limit of the Bowman membrane. This type of dissection is little traumatic and permits easy and accurate restoration of the original anatomical relationships. A thin and highly-vascularized layer of connective tissue—called the episclera—is located below the Tenon’s capsule. Consequently, from the outside to the inside, there is the alternation of highly-vascularized layers, such as the conjunctiva and the episclera, and completely avascular layers, such as the Tenon’s capsule and the sclera