Ophthalmologists most often use a corneal incision. These small incisions are typically 2–3 mm wide, just large enough to accommodate the foldable IOL after phacoemulsification. They generally have little or no effecton pre-existing astigmatism (a common imperfection in the eye's curvature).
Globe stabilization is important in corneal incisions, especially if the process is performed with topical anesthesia. Fixation rings,0.12 mm toothed forceps or instruments supplying counter pressure can be used to stabilize the globe as the incisions are made.
The incisions can be made superiorly, temporally or at the steepest axis of the cornea, depending on the surgeon’s preference.
One common approach for the clear corneal incision is a multiplanar incision using a vertical corneal groove.
In the technique, a metal knife is used to create a 0.3 mmdeep groove perpendicular to the corneal surface.
Another blade is inserted in the groove, and its tip is then directed tangential to the corneal surface, thereby creating a 1.5-mm tunnel through the clear cornea into the anterior chamber.
This multiplanar incision architecture is usually watertight. A variation on the multiplanar incision involves making a deeper vertical groove and creating a hinge.
Another approach is the beveled, multiplanar self-sealingincision, a beveled 3-mm diamond 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.
This technique ideally creates a 3 × 2-mm corneal incision that is watertight. Disposable steel blades can also be used to create these incisions. Newer beveled, trapezoidal diamond blades have been developed for self-sealing clear corneal incisions.
Such blades can be advanced in one motion and in one plane,from 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 and then advanced into the anterior chamber in one smooth, continuous motion.
Regardless of which type of clear corneal incision is used,the goal is to keep the incision just large enough to accommodate the folded IOL with its inserter, generally 2.7–3.2 mm.
A third approach is the “near clear” approach, in which the incision begins within the vascular arcade. Proponents of this approach cite better closure and reduced incidence of induced astigmatism.
However, slight bleeding may occur during the surgery, and a subconjunctival hemorrhage may be present post operatively.
Advantages of Incision of the Cornea:
Avoids dissection of Tenon’s capsule and of the conjunctiva, which decreases the risk of bleeding(e.g., in patients on anticoagulants).
Creates a self-sealing incision that does not usually require sutures and allows for rapid visual rehabilitation.
Offers better accessibility because brow obstruction is eliminated with a temporal approach.
Offers anexcellent red reflex.
Spares the superior conjunctiva for subsequent surgery (e.g., glaucoma filtering procedures or aqueous shunt surgery).
Avoids the need for a traction suture.
Disadvantages of Incision of the Cornea:
Need for the surgeon to adapt to a different surgical position.
Lack of forehead support for the surgeon’s hands (although a wrist rest can be used).
Development of corneal striae intra-operatively if incision extends too far anteriorly, with reduced visualization.
Need to enlarge the incision for use of non-foldable IOL (e.g., anterior chamber IOL ACIOL).
Difficulty in converting to a manual expression ECCE technique.
The proximity of instruments to the corneal endothelium during surgery.
Possible corneal thermal burns.
Higher incidence of endophthalmitis in some studies.