November 2012

 

RESIDENTS

 

Cataract tips from the teachers

The first cut is the deepest


 

Sherleen Chen, M.D.

Assistant professor of ophthalmology Harvard Medical School Director of Cataract and Comprehensive Ophthalmology Massachusetts Eye and Ear Infirmary

Roberto Pineda, M.D.

Assistant professor of ophthalmology Harvard Medical School Director of Refractive Surgery Massachusetts Eye and Ear Infirmary

All phaco surgeons have at some point directly experienced the veracity of the statement, "Each step of phaco builds upon the preceding step." As the initial step of phaco, the importance of wound construction cannot be overemphasized. Successfully performed, its relevance can fade into the background as the ensuing steps of phaco more dramatically unfold. But when poorly constructed, cataract incisions can become a source of continued struggle and, unfortunately, complication. Whether too tight or wide, long or short, anterior or posterior, each compromise has its own surgical consequence. In this column, three expert teachers share their techniques for teaching, learning, and troubleshooting cataract wound construction.

Sherleen Chen, M.D., and Roberto Pineda, M.D.

 

Jose de la Cruz, M.D.

Assistant professor, Department of Ophthalmology Director, Millennium Park Eye Center University of Illinois Eye and Ear Infirmary, Chicago

Dr. de la Cruz: In order to be successful at wound construction, we need to understand the three goals in corneal incisions: adequate size, shape, and architecture. This is true for both types of cataract wounds, clear corneal as well as scleral tunnel incisions. I will focus on the clear corneal incision, since it is currently favored for phacoemulsification. The size of the wound will be dictated by the instruments used during surgery, as well as the type and size of intraocular lens to be implanted. I teach our residents to construct their wounds with a 2.4 mm keratome blade. This size allows for a snug fit of the phacoemulsification probe and sleeve, allowing for optimal fluidics. This same size wound is appropriate for most one-piece IOLs without having to expand the wound or inducing any significant amount of astigmatism. Ideally, I like to see a clear corneal wound tunnel that is as long as the width of the wound. Too short of a tunnel increases the risk of iris prolapse. Too long and the entry is too anterior, increasing the possibility of distorting the wound and affecting visibility.

Our preferred shape for clear corneal incisions is a square or trapezoid. With the recent availability of a femtosecond cataract system in our institution, we are now more accurately constructing trapezoidal wounds that keep our entry in the anterior chamber at 2.4 mm and 2.7 mm at the corneal limbal end, allowing a greater angle of movement without wound distortion. When we teach architecture to our residents, we all have different preferences ranging from uniplanar to triplanar wound construction. Attempting multiplanar wounds is where I see the inadvertent nicking of the capsule entering the anterior chamber with the keratome vertical. To avoid this, I teach our residents to first have counter pressure diametrically opposite to where the wound is being constructed. I prefer using .12 forceps wide open resting on the conjunctiva. This gives me confidence that it will be a controlled entry into the anterior chamber. In addition to this, I ask the resident to enter the cornea from the edge of the limbus with a slight "push down, move forward, push down movement" without pointing the tip of the keratome vertically. This allows a more controlled entry, eliminating the possibility of nicking the anterior capsule and still having a wound that's multiplanar and of adequate length.

Rebecca C. Metzinger, M.D.

Associate professor of ophthalmology Tulane University Health Sciences Center Department of Ophthalmology Chief of ophthalmology Southeast Louisiana Veterans Healthcare System, New Orleans

Dr. Metzinger: In teaching cataract surgery to novice surgeons, I start by having them think about basic wound construction. In order to be self-sealing, watertight incisions, the incisions are typically made in a triplanar fashion. It is important that the beginning surgeon understands that this means there are three separate parts or "planes" of the incision, and he or she needs to concentrate on how each part of this incision is made. The clear corneal wound (Figure 1a) and the scleral tunnel (Figure 1b) are essentially constructed the same way, but the incision is simply longer (and a bit more involved) for a scleral tunnel.

Many different blades and combinations of blades are available to the beginning surgeon. I suggest using only the metal keratome blade with the addition of a crescent blade for cutting the sclera in scleral tunnel incisions. Once the basic principles of wound making have been learned and achieved, residents can then try other types and combination of blades.

Clear corneal incisions

The clear corneal incision (once the eye is filled with viscoelastic) is started by stabilizing the globe with .12 forceps and then making an approximately thickness groove with the blade perpendicular to the surface of the cornea on or just anterior to the limbus. For the beginning surgeon, it is typically easiest to do this with one side of the keratome blade. This groove should be roughly 1-2 mm in length. The tip of the keratome is then placed in the groove with the heel of the blade down. The blade is tunneled upward into the clear cornea for approximately 1 millimeter. I highly recommend that the novice utilize a keratome blade that has a horizontal mark on the surface to indicate the correct distance of this tunnel (Figure 1a, upper left corner). Once the tunnel is made in clear cornea, the heel of the keratome is raised and the tip pointed down until wrinkling around the tip is seen. The anterior chamber is entered with the blade to its full width and then removed. The end result will be a watertight triplanar clear corneal incision. Pitfalls encountered while making this incision include: entering straight into the anterior chamber, thus not being a self-sealing incision, forcing the blade forward or out too fast, which makes the incision too wide and thus not watertight during phaco, poor stabilization of the globe with ripping of the tunnel with the blade, thus having issues of not being watertight, and an entrance into the anterior chamber too close to iris root, thus causing issues with iris prolapsing out of the wound.

Figures 1a and 1b. The clear corneal wound (1a) and scleral tunnel (1b) are essentially constructed the same way, but the incision is longer and more involved for a scleral tunnel Source: Son Ho, M.D.

Scleral tunnel incisions

The scleral tunnel incision requires more steps and can be more challenging to the beginning surgeon. The first step in this type of incision is to perform a 5 mm conjunctival peritomy at the limbus where the incision will be made. Blunt dissection of Tenon's is performed followed by hemostasis with electrocautery. The scleral tunnel incision is then started by stabilizing the eye with .12 forceps and making an approximately thickness groove with the blade perpendicular to the surface of the sclera 1-2 mm posterior to the limbus. This groove should be approximately 3 mm in width (enough to easily accommodate the metal keratome). The sharp edge of the crescent blade (#66 blade) is typically used to make this groove, but a #74 or #64 blade can be utilized for this purpose. The tip of the crescent blade is then placed in the groove and with the blade heel down, tunneled forward into the sclera by gentle circular movements. Once the blade has advanced to clear cornea, the heel of the blade remains down but the tip is elevated to tunnel slightly forward into clear cornea. The crescent blade is removed. The metal microkeratome is then placed into the tunnel and up into clear cornea, with the heel down. As with the clear corneal incision, after the keratome is tunneled 1 mm into clear cornea the heel of the keratome is raised and the tip pointed down until wrinkling around the tip is seen. The anterior chamber is entered with the blade to its full width and then removed. The end result is a watertight triplanar incision. Pitfalls encountered while making this incision include: a thin scleral flap that may tear and interfere with being watertight during phaco, cutting too deep into sclera, which could lead to injury, disinsertion, or bleeding from the ciliary body, globe perforation and difficulty during phaco, entering straight into the anterior chamber too close to the iris root causing issues with iris prolapse from the wound, bleeding from scleral or episceral vessels, which can interfere with visualization during the case, and a poorly closed scleral incision, which can lead to bleb formation or potential infection.

I encourage all the residents to get bovine or pig eyes from the butcher or eyes not suitable for transplantation from the local eye bank and practice making these incisions many times before performing their first surgery. Hopefully with practice and using the techniques I have described, they will avoid the pitfalls above.

Jessica Ciralsky, M.D.

Assistant professor of ophthalmology Weill Cornell Medical School New York

Dr. Ciralsky: In cataract surgery, every step builds upon the previous step. Since clear corneal and scleral tunnel incisions are initial steps, it is essential to have proper wound construction for successful cataract surgery. A poorly constructed wound may lead to wound leakage, shallowing of the anterior chamber, and ultimately, complications.

Most wet labs use porcine eyes to practice cataract surgery. Although porcine eyes are not a perfect substitute for the human eye, the corneal similarities make them ideal for learning wound construction. The tactile feedback provided allows residents to get comfortable with the "feel" of the instruments and tissues. Our residents are required to practice wound construction in supervised wet labs prior to starting cataract surgery.

Several principles apply when teaching wound construction both in the wet lab and operating room. 1) Prepare the eye: The eye must be firm, from generous viscoelastic application through the paracentesis site, prior to making the main incision. A firm eye is more stable, less prone to distortion, and allows more predictable wound construction. 2) Stabilize the eye: Using a second instrument in the sideport incision is my preferred method for securing the eye. This technique is easy to teach and easy to master. 3) Use familiar instruments: Disposable stainless steel blades are my favorite because they provide better tissue resistance feedback and can be used in practice wet labs.

For clear corneal incisions, incision location, shape, and size are all important. I place incisions at the anterior limbus to incorporate vascular tissue to help with wound healing. I prefer a biplanar incision. Start with the heel of the blade flush against the sclera and then advance 2 mm within the plane of the cornea before lifting the heel of the blade and entering the anterior chamber. If possible, obtain keratomes with 2 mm depth marks for beginning cases. I prefer 2.2 mm keratome incisions, if available, as square incisions have been shown to be the most stable.

For scleral tunnel incisions, incision site preparation and incision architecture are critical. Adequately prepare for the incision by making peritomies larger than the planned incisions and achieving good hemostasis. Correct incision configuration is accomplished by consistently creating partial thickness scleral grooves and tunnels and by avoiding second planes with the introduction of the keratome. Novice surgeons frequently create scleral grooves that are too deep or tunnels that are too shallow. Practice makes perfect. A good wound sets the stage for successful surgery.

Editors' note: Dr. de la Cruz has financial interests with Alcon (Fort Worth, Texas). Drs. Ciralsky and Metzinger have no financial interests related to this article.

Contact information

Ciralsky: jessciralsky@gmail.com
de la Cruz: 312-996-2020, josedlc@uic.edu
Metzinger: Rebecca.Metzinger@va.gov

The first cut is the deepest The first cut is the deepest
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