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Construction of corneal phaco incision key to cataract surgery
The incision affects corneal astigmatism, phaco fluidics and resistance to infection.
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 Uday Devgan |
The primary phaco incision is one of the most critical steps of cataract surgery because it significantly influences the fluidic balance, infection resistance and astigmatic result of the procedure. The corneal phaco incision must be properly constructed and placed at an appropriate meridian to optimize the phacoemulsification surgery and to maximize the patient’s visual outcome.
Incision placement
The phaco incision can be placed in the peripheral clear cornea, at the limbus or in the sclera. A completely avascular incision may not have the same long-term healing ability as an incision that has some degree of vascularity. For this reason, slightly nicking the limbal vessels during incision construction is advised. Scleral incisions typically require dissection of the overlying conjunctiva for access as well as cautery to achieve hemostasis, but they may have a more stable closure.
Every corneal incision will induce some degree of astigmatic change, depending on the location, architecture and width. Because of the natural asymmetry present in the anterior segment anatomy, the superior limbus is closer to the visual axis than the temporal limbus and it has more of an astigmatic effect given the same size incision. If a typical temporal incision induces 0.5 D of flattening at that meridian, then expect the superior incision to cause as much as 1 D of flattening at its axis. This is one of the reasons why temporally placed incisions are often preferred for cataract surgery (Figure 1).
 Figure 1. Due to the natural asymmetry of the eye, the superior limbus (blue) is closer to the central visual axis than the temporal limbus (yellow) and has more of an astigmatic effect given the same size incision. Images: Devgan U |
Incision dimensions
The phaco incision width must be matched to the size of the phaco probe in order to achieve balanced fluidics during surgery. Most phaco machine platforms have options for various sized phaco tips, with the standard being about 2.8 mm wide with options down to 2 mm or even smaller. Because heat is created with the ultrasonic vibrations of the phaco tip, we usually want incisions that are slightly leaky and we want phaco needles to have protective silicone sleeves. This egress of balanced salt solution around the phaco tip allows for cooling, but too much outflow will cause an imbalance of the fluidics and lead to an unstable anterior chamber. This is why it is important to use the correct width incision for your particular phaco tip.
Incisions that are wider, are closer to the central cornea and have a shorter tunnel length will induce more astigmatic flattening at the meridian of placement. If an eye has no pre-existing astigmatism, then the ideal corneal cataract incision would be placed temporally, far from the visual axis, and would have a long tunnel length and a narrow width. This is a case in which moving from a standard phaco incision of 2.8 mm down to a microincision of approximately 2.2 mm or smaller would be preferred. Conversely, if an eye has significant against-the-rule astigmatism (steeper at 180°), then the incision could be constructed to be wider, with a shorter tunnel length, but still at the temporal position. Some surgeons even advocate using a second, paired corneal incision opposite of the main phaco incision to induce further flattening in cases of higher astigmatism.
 Figure 2. The diamond keratome is used to make a temporal phaco incision at the steep meridian (15° in this case) by starting at the very periphery of the cornea (top frame) and slightly nicking the limbal vessels. The blade is advanced in a single plane until the tip just starts to pierce Descemet’s membrane (middle frame) and is then fully advanced to create a square, valve-type incision (bottom frame). |
Incision architecture
Many types of corneal phaco incisions have been described, including those with one, two or even three planes, and others with a hinge function such as the Langerman style. Other incisions are created in a trapezoidal manner with the inner width of the incision different from the outer width. There are many variations, but all good incisions have common characteristics: They are well balanced, watertight and stable.
While corneal stromal hydration can be used to help ensure closure of the incision, the most appropriate treatment for a leaking incision is placement of a suture. A poorly sealed incision can wick contaminants from the ocular surface into the eye and may increase the risk of complications such as endophthalmitis. Healing of corneal tissue is slow and occurs over the course of months to years, with slightly vascular incisions achieving stability somewhat faster than avascular ones.
The corneal phaco incision is more than the access point for completing the cataract surgery; it is also a refractive tool that can be used to address corneal astigmatism, a barrier to infection and a large determinant of phaco fluidics. Start your next surgery with a well-constructed phaco incision and realize these benefits for your patients.
- Uday Devgan, MD, FACS, FRCS, is in private practice at Devgan Eye Surgery in Los Angeles and Beverly Hills. He can be reached at 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025; 800-337-1969; fax: 310-388-3028; email: devgan@gmail.com; website: www.DevganEye.com.
- Disclosure: No products or companies are mentioned that would require financial disclosure.