Construction of the corneal incision during the iridectomy. The incision is created just in front of the limbus (0.5–1 mm) at the anterior edge of the limbal vessels. It is created with a 15° knife and must be 3 mm long. It is recommended to initially extend the incision to the Descemet membrane and then penetrate the AC for the 3 mm of the incision, slightly detaching the corneal tissue upwards with toothed forceps. With the approach in clear cornea, the surgeon must enter the AC perpendicular to the cornea to allow access to the root of the iris; nevertheless, the basal iridectomy can sometimes prove difficult in technical terms. Prior to the iridectomy procedure, the surgeon can opt to inject 0.5–2 ml of acetylcholine hydrochloride into the AC. This will assist the contraction of the iris sphincter and stimulate miosis. The injection can be performed through this or a second incision created in the temporal sector of clear cornea (paracentesis). Some authors recommend an additional injection of 1% lidocaine anesthetic in the AC with a 30G cannula. The iridectomy can now be performed (Fig. 6.3)

Basal Iridectomy. In the basal iridectomy procedure , the iris is caught and carried outside of the AC through the scleral opening, with dedicated toothed forceps with fine arms (iris forceps) or with Colibrí forceps. Sometimes, once the AC has been opened, the iris will tend to prolapse spontaneously through the incision. The iris is cut peripherally, in parallel to the limbus, using Vannas or DeWecker scissors. The surgeon must pay attention to the position of the stroma and the pigmented layers of the iris when he is creating the full-depth iridectomy. Ideally, the peripheral iridectomy should lie between the external third and the middle third of the iris: the surgeon must avoid cutting the larger iris vessels in this area. During the iridectomy, it is essential that the surgeon checks the position of the pupil to avoid an excision that lies excessively close to the pupil. The surgeon must not remove tissue that is excessively posterior: this should prevent rupture of the base of the iris, creation of an iridodialysis, damage to the ciliary body or intraocular bleeding

Manoeuvre that facilitates iris prolapse prior to the iridectomy Prior to performing the iridectomy, some surgeons recommend delicately prolapsing the iris through the incision, exerting slight pressure on the posterior lip of the incision with a blunt instrument. Once the iridectomy has been completed, in most cases, the iris will spontaneously tend to return into the AC through the incision and the peripheral iridectomy can be visualized through the cornea. In the event the iris remains trapped in the incision, the problem will be often be resolved by applying light pressure on the scleral side of the incision with an iris spatula. If this maneuver is unsuccessful, the iris can be repositioned in the AC by delicately touching the cornea with a blunt instrument (for example, an iris spatula or a muscle hook), smoothing the tissue with a centrifugal movement from the center of the cornea to the limbus. In the event of further failure, injecting BSS in the direction of the incision should return the iris to its rightful position. Generally-speaking, the AC is not lost during this procedure and consequently, does not need to be reformed. Once the surgeon has repositioned the iris in the AC, he must check that the iris is circular and that the iridectomy has included the pigmented layer: he must identify the red reflex through the iris fistula with back lighting, using the co-axial light of the operating microscope or by directly observing the presence of pigment on the piece of tissue removed. Some authors have suggested an iridectomy with a vitrectome as an alternative to the traditional procedure we described above. The final phase of the procedure involves placement of the sutures. As the incision in clear cornea is not a tunnel, the closure of the incision will be a more critical phase and will often require a suture in 10.0 nylon to seal the incision and prevent leakage. One or two suture points are passed full-depth at the center of the cornea. These will be tightened to ensure the correct positioning of the incision edges, without pulling excessively on the tissues. The sutures are then recessed in the tissue. The advantage of the approach in clear cornea is that the cornea itself is not manipulated, an extremely important factor in view of a potential filtering procedure at some stage in the future. Variations of this technique include the creation of an incision; as mentioned previously, some authors prefer a limbal approach, others prefer the approach in clear cornea and others prefer the sclera-corneal tunnel. Charleux described a variation of the corneal approach : the incision is created in a slightly anterior position with respect to the limbus, though at a different angle. The cut is described as “inverted” because the blade resting on the peripheral cornea is tilted in an antero-posterior direction to direct the lip towards the irido-corneal angle, and creates a chamfered connection. The iris is caught with forceps and, given the orientation of the cut, the surgeon will be certain he is correctly performing the basal iridectomy. Moreover, it will not be necessary to close this cut with a suture as it is valved and self-sealing