(a–f) Front and cross-sectional view of a self-sealing MSICS wound. Frown incision with the center of the arch being around 2–3 mm from the limbus, the sides 4 mm away (a), and depth of the scleral wound being one-third to half the thickness of the sclera (d). Dissection is continued 1–1.5 mm into the clear cornea, such that the total length of the tunnel is 4 mm in the center and 5–6 mm at the sides (b, e). Entry is made at the anterior end of the tunnel with a sharp keratome (c) to make a “triplanar” incision (f)
No additional anesthesia is required to convert to MSICS if the phacoemulsification was under peribulbar block. If the surgery was under topical anesthesia, it can be augmented with a sub-Tenon’s anesthesia [7, 8] given intraoperatively (Fig. 19.2). This will provide additional anesthesia and akinesia. A 3 cc syringe is prepared with equal parts of 2 % lidocaine and 0.75 % bupivacaine. A curved lacrimal cannula is attached to the syringe. The temporal quadrant is preferred to avoid inadvertent damage to the oblique muscles. Holding the conjunctiva and Tenon’s capsule 7–10 mm from the limbus, with fine Lim’s forceps, a small incision is made with Westcott scissors down to the sclera. The Westcott scissors are redirected backward with the curve toward the globe, and the Tenon’s space is bluntly dissected in that quadrant, to a point beyond the equator of the globe. The lacrimal cannula is introduced through this opening, with the tip beyond the equator, before injecting 2–3 cc of the mixture. If the cannula is in the right plane, it should flow without resistance and cause only minimal chemosis. Otherwise, the cannula is withdrawn, and the Tenon’s space dissected posteriorly, before injecting further. A pair of sterile cotton applicators can be used to spread the anesthetic solution uniformly into all the quadrants.
Sub-Tenon’s anesthesia. (a) The conjunctiva and Tenon’s capsule are held 7–10 mm from the limbus with Lim’s forceps and incised down to the sclera. (b) Blunt dissection into the sub-Tenon’s space with the curve of the Westcott scissors directed toward the sclera. (c) Injecting the anesthetic solution beyond the equator of the globe. (d) A well blocked eye with minimal chemosis at the conclusion of block
19.3 Method of Converting from Phacoemulsification to MSICS
There are two methods of converting from phacoemulsification to MSICS (Fig. 19.3). If the original incision is clear corneal, a sclerocorneal tunnel is made 90° away (superior if a temporal clear corneal incision has been made, and vice versa). If the initial wound was sclerocorneal, one could modify the same to convert it into an MSICS wound.
(a–f) The two methods of converting from a phacoemulsification to MSICS. (a–c) Conversion to an MSICS wound remote from the clear corneal phaco wound. (d–f) Conversion of a sclerocorneal phacoemulsification wound into an MSICS wound
As described in another chapter, it is important to not withdraw the phacoemulsification needle from the eye on noticing a PCR or ZD. While the phacoemulsification and the vacuum are stopped immediately, the irrigation is kept on, that is, one moves from foot pedal position 3 to foot pedal position 1. A dispersive ophthalmic viscosurgical device (OVD) is then injected into the area of PCR or ZD before stopping the irrigation and drawing the phacoemulsification needle out of the eye. This prevents collapse of the AC and further vitreous herniation into the AC and wounds.
We will first describe the creation of an MSICS tunnel remote from the original phacoemulsification wound (Fig. 19.4). The original clear corneal wound is abandoned, and if necessary sutured before shifting to a different site for the sclerocorneal tunnel. This necessitates changing the position of the surgeon vis-a-vis the patient, from temporal to superior position, or vice versa. A peritomy is made followed by adequate coagulation of the bleeding points. One should avoid over-cauterization, as this may precipitate scleral thinning or melting. A partial thickness curvilinear 6 mm scleral groove is then made with the arch toward the limbus (frown incision) . The center of the arch is around 2–3 mm from the limbus, while the sides are 4 mm away (Fig. 19.1a). Various other incisions have been described, such as straight and chevron , but the frown incision is the most secure with the least surgically induced astigmatism. Fresh paracenteses are made, as the original ones may not be convenient to use after changing the surgical site. Using a crescent blade, the sclera is dissected at the same plane along the entire extent of the incision. The depth of the tunnel is one-third to half the thickness of the sclera (Fig. 19.1d). The depth is judged to be correct when the crescent is just visible through the sclera (Fig. 19.4c). While dissecting, the heel of the crescent blade should be flat on the globe to maintain a uniform depth throughout the tunnel. The dissection is continued up to 1–1.5 mm into the clear cornea (Fig. 19.1b, e). The final width of the tunnel (distance from the scleral incision to the corneal entry at the level of the Descemet’s membrane) is 4 mm at the center and 5–6 mm at the sides. While dissecting the cornea, a forward-and-backward movement is used, making sure that the tissue is cut during the backward stroke. Scleral pockets are created at the two ends of the tunnel to accommodate the nucleus during delivery. A sharp keratome is used to enter the anterior chamber at the anterior extent of the corneal dissection and extended along the entire length, taking care to cut the cornea only during the forward stroke of the keratome. This wound is stable and secure, and if created with care, sutureless with predictable and stable astigmatism.
(a–f) Conversion of phaco to MSICS due to loss of rhexis in a brown cataract. The sclerocorneal MSICS wound (b, c) is fashioned 90 °away from the temporal clear corneal phacoemulsification wound (a). The 6 mm “frown” incision is 2 mm away from the limbus at the center and curves away from the limbus at the sides. Dissection is 1.5 mm into the cornea, such that the length of the tunnel at the center is 3.5–4 mm. After entry with a sharp keratome (d), the nucleus is dislocated into the AC with a Sinskey hook (e) and expressed out with an OVD (f)
Beginning surgeons could think of modifying their phacoemulsification wounds while operating on challenging cases such as posterior polar cataract, brunescent cataract, subluxated cataract, complicated cataract, etc. Here, one could fashion a sclerocorneal incision instead of a clear corneal one. This incision can be converted into a sclerocorneal tunnel with some modifications (Fig. 19.5). A small peritomy is done superiorly or temporally depending on the site of the wound. This usually does not require cauterization. Depending on the size of the phacoemulsification tip, a 2.2 or 2.8 mm sclerocorneal incision is made starting 1 mm posterior to the limbus. The corneal entry is made 1 mm anterior to the limbus giving a width of 2 mm. Wounds with a long anteroposterior diameter render phacoemulsification difficult by hampering the movement of the phacoemulsification needle and reducing visibility due to the corneal striae produced. For converting this wound into a sclerocorneal tunnel, the peritomy has to be enlarged and the bleeding vessels coagulated. With the aid of a 15° lance tip keratome or a #15 Beaver Blade, two partial-thickness scleral grooves are fashioned starting from the edges of the scleral portion of the phacoemulsification incision. These are directed 2–3 mm laterally and posteriorly at the angle of 45°. Introducing the crescent blade into the original phacoemulsification tunnel, the dissection is extended sideways along the grooves made into the sclera and cornea using backward and forward movements, again cutting during the backward stroke alone. By keeping the crescent blade flat, one maintains the dissection in the same plane. Posteriorly, the dissection follows the incision already made, and the anterior extent is 1–1.5 mm into the clear cornea. Once the dissection of the tunnel is complete, the extension into the AC is completed with the same crescent blade, as the entry has already been made for the phacoemulsification tunnel. The eye should be kept firm during the dissection, as a soft eye causes the wound to be irregular. A good dispersive or viscoadaptive OVD prevents collapse of the AC while dissecting the sclerocorneal tunnel with an open phacoemulsification wound. It is important to note that a clear corneal phacoemulsification tunnel cannot be converted into a sclerocorneal tunnel. A wound thus created is not self-sealing and requires sutures for closure, while a sclerocorneal phacoemulsification wound can be converted into a sutureless MSICS tunnel.