Clear Corneal Incision
During phacoemulsification, most surgeons use a clear corneal approach for the main incision (Fig 8-7). These small incisions are typically 2.2–3.2 mm wide, just large enough to accommodate the phaco handpiece and allow insertion of the IOL. Globe stabilization is important in clear corneal incisions, especially when the procedure is performed with topical anesthesia. Fixation rings, 0.12-mm toothed forceps, or instruments supplying counterpressure can be used to stabilize the globe as the incisions are made.
Various types of corneal phacoemulsification incisions have been described, including biplanar and multiplanar incisions. Regardless of which type of clear corneal incision is used, an important objective is to create a stable, watertight incision to minimize the risk of wound leak and endophthalmitis. In the multiplanar technique, a diamond or metal blade is used to create a 0.3-mm-deep groove perpendicular to the corneal surface. Another blade is inserted into the groove, and its tip is then directed tangentially to the corneal surface, creating a tunnel through clear cornea into the anterior chamber.
Another approach is the beveled, self-sealing biplanar incision. A beveled blade is flattened against the eye, and the tip is used to enter the cornea just anterior to the vascular arcade. The blade is advanced tangentially to the corneal surface until the shoulders of the blade are fully buried in the stroma. The point of the blade is then redirected posteriorly so that the point and the rest of the blade enter the anterior chamber parallel to the iris.
Figure 8-7 Illustration of the architecture of clear corneal incisions: biplanar (left) and triplanar (right).
(Illustration developed by Lisa Park, MD, and rendered by Christine Gralapp.)
Self-sealing clear corneal incisions can be created with beveled, trapezoidal diamond blades. Such blades can be advanced in one motion and in one plane, from the clear cornea into the anterior chamber. The blade is oriented parallel to the iris, and the tip is placed at the start of the clear cornea, just anterior to the vascular arcade. The blade is tilted up and the heel down so that the blade is angled 10° from the iris plane; it is then advanced into the anterior chamber in one smooth, continuous motion.
Another type of incision uses the “near-clear” approach, in which the incision begins within the vascular arcade. Proponents of this approach cite better wound closure and a reduced incidence of induced astigmatism. However, there may be slight bleeding during surgery, and conjunctival ballooning may occur. In addition, a subconjunctival hemorrhage may be present postoperatively.
Clear corneal incisions may also be made using a femtosecond laser; see the section Alternative Technologies for Cataract Extraction for further discussion.
Regardless of which type of clear corneal incision is used, the length of the wound should permit optimal visualization and instrument manipulation during phacoemulsification. If the corneal incision is too long, the surgeon may have problems manipulating the phaco tip within the anterior chamber and corneal striae may reduce visibility as the surgeon manipulates the handpiece. If the tunnel is too short, the incision may not seal postoperatively. The phaco tip may also abrade the iris, causing atrophy and possible pupil distortion.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.