This column is one in an invited series by Dr. Osher. The series highlights techniques that may be helpful in particular to young practitioners.
If each step of the operation had a personality the incision would be chronically depressed. Why? Because so little attention is given to this crucial step of the operation. Can you imagine an Olympics without an opening ceremony? Yet if you compromise incision construction, there is a price to be paid later in the operation.
Let's begin with the obvious. When the external incision is too long, there is more fluid leakage and the chamber is more difficult to maintain. Induced astigmatism is related to incision length. When the external incision is too short, the surgeon may feel “oar-locked” when performing the phacoemulsification or the irrigation/aspiration. It is also more difficult to inject the intraocular lens (IOL) through a tight incision, which I described as a complication when microcoaxial phacoemulsification was introduced in 2007.1 There is also a greater likelihood of compressing the infusion sleeve, which can lead to thermal consequences. When the incision is too far posterior, there may be inadvertent pressure on the globe that can cause positive pressure and chamber shallowing. When the incision is too far anterior, endothelial cell loss may occur when the cornea is distorted, which also compromises visualization. When the incision is too shallow, a watertight closure may not be possible. When the incision is too deep, iris prolapse may be encountered. When I designed one of the first micrometer diamond knives in the early 1980s, we had an epidemic of hypotony due to penetration into the suprachoroidal space. To avoid any of these complications, the incision should be meticulously constructed.
The amount of surface area is important for consistent watertight closure. Paul Ernest, MD, from Michigan raised the intraocular pressure (IOP) in cadaver eyes and demonstrated that the square incision resulted in optimal self-sealing closure.2 Based on his study, I worked with BVI to develop a guarded knife with a snub-nosed blade that was scored to facilitate a 2-plane or 3-plane square incision for microcoaxial phacoemulsification. Although the closure was consistently watertight, it was difficult to inject a full size IOL through a 2.2 mm opening when the incision was used as an extension of the cartridge.
The solution was a flared incision, which I published in the Journal of Cataract & Refractive Surgery, measuring 2.2 mm on the outside and 2.4 mm on the inside.3 This was constructed by simply withdrawing the knife while it was still in the tunnel and angling first to the left and then to the right (Figure 1).3 Not only was it easier to use the incision as the extension of the cartridge without fear of the IOL getting stuck in the tunnel, but there were other advantages too. The internal flare allowed better maneuvering of the ultrasound and irrigation/aspiration tip without causing the eye to move due to oar-locking. Moreover, there was less compression of the irrigation sleeve with some leakage that resulted in a lower temperature profile within the incision.
Surgeons have different preferences for a 1-plane, 2-plane, or 3-plane incision. David Langerman, MD, introduced the grooved incision, and Richard Kratz, MD, taught the world the scleral tunnel incision.4 I personally like the consistency of a 3-plane incision with a groove, an uphill tunnel, and a final downhill entry. It is important to keep in mind the chamber depth before the final entry to avoid inadvertent penetration of the anterior capsule or damage to the iris. It is also important to avoid compressing the sleeve during the phacoemulsification, which can cause a thermal injury. Years ago, it was not uncommon to have a significant “fish mouth” because of thermal contraction of collagen, which caused high astigmatism, terrible wound leak, and was nearly impossible to close. I published the gape suture, which was a method of adding tissue by using a horizontal suture from the back of the roof to the front of the floor.5 Nowadays, we do not see these horrible thermal injuries, but it is possible to have a microthermal injury by compressing the sleeve against the lateral wall of the incision, as initially described by Hiroko Bissen-Majima, MD.6 I subsequently published the shark fin sign, which was due to focal collagen damage observed at the slitlamp the day after surgery.7 A final word of caution pertains to the introduction of any instrument that should be depressed in the incision on entry to avoid damage to Descemet membrane. But that's another story.
What about ocular sealants? ReSure sealant (Ocular Therapeutix) was approved by the U.S. Food and Drug Administration in January 2014. At that time, I began using ReSure in cataract operations combined with vitreoretinal procedures. After routine hydration of the flared incision, a Weck-Cel (Eye Care and Cure) sponge was used to dry the surface and the ReSure sealant was applied. The retinal procedure followed, which included trocar insertion and scleral depression. To determine the efficacy and safety of the sealant in combined procedures, one of our senior medical students, Andrew Stephenson, BS, independently reviewed the medical records of 29 eyes of 28 patients.
The results showed no instances of either wound leak or dehiscence during surgery, and no incision-related complications were identified on the first postoperative day. Hypotony was present in 2 patients with an IOP less than 6 mm Hg, presumably related to the trocar insertion rather than the watertight flared incision. The average IOP on postoperative day 1 measured 15.6 mm Hg, while the average pressure in the fellow eye measured 14.3 mm Hg. When the patients were examined 3 to 4 weeks later by the cataract team, all incisions were noted to be well healed and all eyes were normotensive. We concluded that ocular sealants are very effective and eliminate the disadvantages of sutures.
It has been satisfying to watch incisions shrink from 12 mm when I watched my father perform intracapsular surgery to 10 mm when extracapsular surgery became popular. Then, the incision was reduced to 6 mm after the phacoemulsification to allow the introduction of a PMMA IOL. When Thomas Mazzacco, MD, developed the foldable lens, the incision shrank to 3 mm and was again reduced to 2.75 mm as smaller tips were designed. I was fortunate to work with Alcon in introducing microcoaxial phacoemulsification through a 2.2 mm incision, which gave superior control of the intraocular environment and induced negligible cylinder.1 Technology will continue to improve, and perhaps someday there won't even be an incision. What an exciting subspecialty we've chosen!
1. Osher RH. Microcoaxial phacoemulsification—part 2: clinical study. J Cataract Refract Surg 2007;33:408–412
2. Ernest PH, Lavery KT, Kiessling LA. Relative strength of scleral tunnel incisions with internal corneal lips constructed in cadaver eyes. J Cataract Refract Surg 1993;19:457–461
3. Osher RH. Internal flare:
modification of wound construction for micro incisional cataract surgery. J Cataract Refract Surg 2012;38:721–722
4. Langerman DW. Architectural design of a self-sealing corneal tunnel, single-hinge incision. J Cataract Refract Surg 1994;20:84–88
5. Osher RH. How do I proceed if I see a small wound burn with whitening of the corneal stroma? How would I close a severe corneal burn? In: Chang D, Kim T, Oetting TA, eds. Curbside Consultation in Cataract Surgery 49 Clinical Questions. Thorofare, NJ: SLACK Incorporated; 2007:97–101
6. Bissen-Miyajima H, Shimmura S, Tsubota K. Thermal effect on corneal incisions with different phacoemulsification ultrasonic tips. J Cataract Refract Surg 1999;25:60–64
7. Osher RH. Shark fin: a new sign of thermal injury. J Cataract Refract Surg 2005;31:640–642