Intraoperative OCT allows analysis of corneal phaco incision
Positioning, tunnel length and architecture are the three most important considerations for a good corneal phaco incision.
The corneal phaco incision is a critical component in the success of cataract surgery. The incision is important for providing intraocular access to remove the cataract and insert the IOL, but it is also critical for maintaining fluid balance within the anterior chamber. An incision that is poorly constructed will limit the access to the anterior segment during surgery, and it can also leak fluid, thereby throwing off the fluidic balance of inflow to outflow, which will result in surge, a destabilized anterior chamber and a higher risk for complications such as posterior capsule rupture.
The incision will have an astigmatic effect that we can attempt to minimize or shift to the steep axis of the cornea. In addition, the incision should seal well with good long-term stability in order to prevent ocular surface contaminants from entering the eye, which could lead to infection and further inflammation. Finally, the incision is your signature on the eye: Even years after the cataract surgery has been performed, the primary evidence of your work is the phaco incision and the capsulorrhexis.
The three most important considerations for an excellent corneal phaco incision are:
The incision should be at the limbus with care taken to barely nick the superficial blood vessels. This will ensure great long-term sealing. You must avoid making a completely avascular incision because the healing is more limited and it can be opened with blunt instruments even years later. The incision should also be radial and aimed toward the center of the pupil, and care should be taken to make it only as wide as the keratome. The specific phaco tip and sleeve require an exact incision width in order to have stable fluidics.
2. Tunnel length
The incision should have a sufficient enough tunnel length to provide good sealing, but not so long as to cause oar-locking of instruments. For most incisions, this means a tunnel length of between 2 mm and 2.5 mm from the corneal epithelium until the endothelium. A short tunnel length will not seal as well because there is less surface area for the valve effect. Too long of a tunnel length will seal well but will restrict the movement of instruments within the eye.
The incision architecture should be such that the roof and floor of the incision are balanced. A single-plane, dual-plane or even triple-plane incision can be done with equally good results as long as they all have a balanced architecture. The most common mistake is starting the incision too superficial with the roof being quite thin as compared with the floor. Once this is noticed by the surgeon, an attempt is made to enter the anterior chamber before the tunnel becomes too long. The error committed is to then “dimple down” by making the angle of the blade steep and diving into the anterior chamber. While this does prevent the tunnel length from extending farther, it also creates an imbalanced incision with a roof that is too thin and a floor that is too thick. At the slit lamp, these imbalanced incisions have a characteristic chevron appearance, and they will induce more astigmatism than a properly constructed incision.
With newer surgical microscopes, there is an ability to perform an intraoperative OCT of the corneal incision. This allows us to see a cross-section of the corneal tissues in two or more planes to better understand the architecture. In the examples shown here, one cataract surgery has a good incision whereas the other surgery has a poorly constructed incision. Both surgeries were performed by the same resident ophthalmologist, on the same day, using the same instrumentation. The resident surgeon has about 100 cases of experience at this point and will certainly blossom into an excellent ophthalmologist.
In the first case (Figure 1), the incision has all three characteristics of a good incision. The positioning is appropriate, right at the limbal vessels, and the incision is radial and of the correct width. The tunnel length is good at a little more than 2 mm. Finally, the architecture is excellent, with good balance between the roof and the floor of the incision. Descemet’s membrane is pierced in a linear manner and not with a chevron appearance.
In the second case (Figure 2), the incision starts appropriately at the limbal vessels and is aimed toward the center of the pupil, but the tunnel length is much too long. This is because the angle of the keratome was too flat and the surgeon made the roof too thin. The keratome was advanced farther into the eye, and when the surgeon realized that it was too long of a tunnel, the “dimple down” error was forced in order to enter the anterior chamber. This results in an incision with imbalanced architecture with a thin roof and a thick floor. In this case, the incision caused 1 D of astigmatism and required a suture for closure.
Previously, we have drawn figures to explain incision construction (Figure 3), and now with intraoperative OCT, we can image the incisions directly to ensure that we are doing the best for our patients. The incision is a critical step of cataract surgery, and by following the guidelines of positioning, tunnel length and architecture, we can ensure the best results for our patients.
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- For more information:
- Uday Devgan, MD, is in private practice at Devgan Eye Surgery, Chief of Ophthalmology at Olive View UCLA Medical Center and Clinical Professor of Ophthalmology at the Jules Stein Eye Institute, UCLA School of Medicine. He can be reached at 11600 Wilshire Blvd. #200, Los Angeles, CA 90025; email: email@example.com; website: www.CataractCoach.com.