Scleral Tunnel Incision
An alternative to the clear corneal incision is a scleral tunnel incision (Fig 8-8). One advantage of this incision is that it may reduce the incidence of both early and late surgically induced astigmatism. Another advantage may be more-controlled conversion to ECCE when this becomes necessary.
For this incision, a limited conjunctival peritomy is created over the intended incision site. The surgeon then clears the overlying Tenon capsule from the sclera and may apply light bipolar cautery to achieve hemostasis. Excessive cautery should be avoided because it can cause scleral shrinkage and postoperative astigmatism.
The scleral incision is usually linear, but it may be either curvilinear (smile shaped, following the limbus, or frown shaped, following the curve opposite the limbus) or chevron shaped. After making the incision, the surgeon uses a blade to enter the scleral groove at a depth of half the scleral thickness, dissecting anteriorly into clear cornea just anterior to the vascular arcade, creating a partial-thickness scleral tunnel. If the scleral groove is entered too deeply, the scleral flap will be very thick, and the blade may penetrate the anterior chamber earlier than anticipated, closer to the vascular iris root. If the scleral groove is entered too superficially, the scleral flap will be very thin and prone to tears or buttonholes.
To enter the anterior chamber from beneath the scleral flap, the surgeon uses a keratome sized to match the width of the phaco tip. The keratome is inserted into the corneal stroma until the tip reaches the clear cornea beyond the vascular arcade. The heel of the keratome is elevated, and the tip of the keratome is pointed posteriorly, aiming toward the center of the lens and creating a dimple in the peripheral cornea. The keratome is then slowly advanced in this posterior direction, creating an internal corneal lip as it enters the anterior chamber.
Figure 8-8 Illustration showing scleral tunnel incision, side view: The initial groove is one-third to one-half of the scleral depth. The incision is traditionally 2–3 mm posterior to the limbus. The tunnel is traditionally dissected past the vascular arcade. A short third plane is made by changing the angle of the blade before entering the anterior chamber.
(Reproduced with permission from Johnson SH. Phacoemulsification. Focal Points: Clinical Modules for Ophthalmologists. American Academy of Ophthalmology; 1994, module 6. Illustration by Christine Gralapp.)
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.