Here’s how to move quickly through the learning curve
By Robert M. Kershner, MD, FACS
I would encourage almost any surgeon who is currently using scleral tunnel incisions to consider switching to topical anesthesia and clear corneal incisions. You will appreciate the time savings these incisions provide, and your patients will love the fact that their eyes are fully functional and appear normal almost as soon as they leave the operating room. But I feel compelled to add the following caution: clear corneal incisions require that you observe a different set of rules than those that apply to scleral incisions. You’ll find that you need to make changes in the way you prepare patients, the way you create and manipulate the incision, and the way you operate through that incision. To help you through the learning curve, consider the following six tips.
1. Minimize eye movement
With topical anesthesia, patients can feel many sensations that they could not feel with peribulbar blocks. Many surgeons have difficulty getting used to this fact, and make mistakes as a result.
Here are a couple of ways to help:
First, use one drop of 2.5% hydroxypropylmethylcellulose, (HPMC), rather than balanced salt solution. When doing scleral tunnel surgery and using a retrobulbar block, our scrub techs routinely direct a stream of balanced salt solution over the ocular surface to keep it clean and moist. This is not a good idea with clear corneal surgery. For one thing, there’s no longer any need to irrigate blood away from the operative field, since clear corneal surgery is bloodless. Second, patients under topical anesthesia feel the BSS and move their eyes when it contacts the surface.
Several ophthalmic products contain HPMC. They include Occucoat, Celluvisc, Refresh artificial tears, and Goniosol. In our practice, we typically transfer a bottle of Goniosol (maintaining sterility) into TB syringes on the morning of surgery. Goniosol is the most viscous at 2.5% HPMC, is optically clear, coats the cornea beautifully, and even provides 1.5X magnification. After you’ve applied one drop onto the center of the cornea, your scrub tech can do something else. The ocular surface is protected.
Second, remember to always warn patients about what you are going to do to them ahead of time. For instance, when placing a speculum, you may want to alert the patient that “you are about to feel some pressure on your eye.”
2. Keep your incision in shape
Unlike scleral tunnel incisions, corneal incisions are not very forgiving. It’s easy to distort, tear or stretch a corneal incision, and when you do, it will leak, induce unwanted astigmatism and heal more slowly. Here are a few basic rules:
• Size matters. The most common error inexperienced surgeons make when constructing clear corneal incisions is to use a keratome that’s too small for the instruments they plan on passing through the incision. This causes stretching or tearing of the incision, and striae that can obscure visualization during the procedure. It can also cause post-operative healing problems. Unlike scleral incisions, corneal incisions do not snap back into place after stretching. If your incision is too small, you will likely wind up distorting the incision when passing instruments through it, causing it to gape like a fish mouth rather than seal shut like a paper cut. The easiest way to avoid this is to use a keratome that is properly sized to accommodate your largest instrument.
Typically, corneal incisions wider than 3.2 mm will induce flattening and unwanted aberration in the refractive power of the central cornea. These incisions usually do not seal on their own, and require suturing. Incisions 3 mm wide or less seal neatly.
• Use the right tools for the job. Standard disposable steel keratomes used routinely for scleral tunnel incisions won’t work for clear corneal incisions. Only very sharp keratomes can atraumatically penetrate Descemet’s membrane.
Some of the most successful and busiest clear cornea surgeons I know are diamond blade users. They use these blades because of their unrivaled sharpness. The cutting edges can be made as thin as 1 µm, enabling these knives to pass through the corneal lamella smoothly and easily, leaving behind an incision as smooth as a paper cut.
However, many surgeons lack the trained surgical team necessary to maintain these expensive instruments. For these surgeons, there is now an alternative. A new clear corneal incision system designed by Becton Dickinson Beaver features a blade that rivals a diamond’s sharpness, contour and geometry, yet is made from surgical steel. The complete disposable kit also includes a fixation ring to keep the eye stable and an inkless marker that helps to mark the proper size, location and configuration of the ideal clear corneal incision. The marking device creates two marks, a curved one where the entrance to the incision should be and a linear mark for the entrance into the eye through Descemet’s. By simply fixing the globe in place with the fixation ring, and marking the incision with the marker, the surgeon can properly position the keratome for the ideal incision. Place the tip of the corneatome on the incision entrance line, aim and line up the blade with the second line mark, then pass the blade into the cornea until it reaches the laser mark on the blade. At this point, the tip will enter the eye at the proper angle and the ideal tunnel length will be achieved automatically. The length to width ratio will be maintained at 3:2, which is proven to be stable.
The keratomes are available in a variety of widths to accommodate whatever phacoemulsification tip and lens insertion method you use. The knife has a specially designed double-bevel slit blade in either angular or straight form for proper clear cornea incision construction and an accurate depth blade to construct the two-step arcuate keratotomy incision.
3. Reduce, don’t induce, astigmatism
Where you make the incision is just as important as how you make it.
Prior to surgery note in the chart the position of the patient’s steepest meridian on the cornea. As all transverse or arcuate corneal incisions flatten the corneal architecture, always locate your incision on the steepest meridian. Can't determine the steepest meridian? Simply refract the patient in plus cylinder or take a corneal topographic map. Placing the incision anywhere other than the steepest part of the cornea will make the astigmatism worse. Since most elderly patients have against-the-rule astigmatism, temporal incisions typically are best. These incisions are also best if the patient has a spherical cornea. The temporal limbus is located further away from the optical center than is the superior limbus, and so temporal incisions will create less induced corneal astigmatism. Patients with significant pre-existing astigmatism may benefit from limbal relaxing incisions or astigmatic keratotomy (keratolenticuloplasty) at the time of surgery.
4. Avoid corneal burns
The best defense against this complication is making a properly sized corneal incision. Incisions that are too small will crimp the irrigation sleeve on your phaco tip, causing the probe’s temperature to skyrocket. In my experience, using thick, cohesive viscoelastics also increases the incidence of wound burn. I use thinner viscoelastics for all my cases.
5. Prevent capsule complications
If you are a beginning clear-corneal surgeon, you will most likely discover that your access and ability to maneuver through the small incision is much less than you are used to. I compare this technique to sewing the wings on a mosquito through the neck of a bottle. Because of this, you may find it useful to make a few alterations in your technique.
The first challenge is making a good capsulorrhexis; this is critical to preventing problems during phaco and IOL implantation. Obviously, you should use the instrumentation with which you are most comfortable, but I happen to like two devices made for me by Rhein Medical for this task. One is a forceps of my own design which allows you to open the capsule and conduct the tear with a single instrument. The other allows you to make the capsulorrhexis through the paracentesis incision even before you ever make the corneal incision. Both save time, are more convenient and reduce wear and tear on the incision.
It’s not uncommon to fumble the capsulorrhexis once or twice as you learn to use the clear-corneal incision. If the tear starts to head off toward the equator, stop, inject viscoelastic to tamponade the lens and push the lens-iris diaphragm posteriorly. This reduces the stress on the capsule from the peripheral zonules. Then regrasp the flap and pull it towards the center of the eye to bring it back into line. Then you can complete the tear.
When you are emulsifying the nucleus, keep the phaco tip within an imaginary triangle right in the central portion of the cataract, as far away as possible from the iris, posterior capsule, and corneal endothelium. This will help prevent damage to all three structures.
If you do break the capsule before you have removed the nucleus, you will need to stop and do a vitrectomy and then remove the remaining lens pieces manually. There are two ways to handle this. You can abandon your clear cornea incision and make a new scleral incision through which to deliver the nuclear pieces, or you can enter your clear-corneal incision along with a left-handed instrument through a paracentesis, securing and removing each piece one at a time.
6. Use injectable lenses
The IOL you use is a matter of personal preference, of course, but for clear corneal incisions I prefer injectable plate-haptic lenses. These make it possible to use a 2.4 mm incision or smaller, which has little impact on corneal cylinder, they are easy to implant in one step and they are fun to use.
There is a downside to these lenses, however. They can be a bear to remove. Because we are squeezing these lenses through such a tight space, they tear on rare occasions. If the tear occurs in the haptic, it’s OK to just leave the lens in place, but if the tear affects the optic, removal is necessary.
When this occurs, I like to employ another Rhein instrument, the Utrata lens snare and forceps. It allows you to cut the lens into tiny pieces and remove them without enlarging the incision.
If you have similar trouble with three-piece silicone or acrylic lenses, you will generally have to enlarge the incision to remove them. And remember, any incision you create that is greater than 3.2 mm should be sutured.
The clear cornea incision is here to stay. More and more surgeons are mastering the finesse of the technique and more and more patients are demanding the rapid recovery and clear uncorrected vision this technique provides. By incorporating these six tips into your approach to cataract surgery, you will save time and avoid trouble. You too, will be a believer-clear cornea is best.
Dr. Kershner is Clinical Professor of Ophthalmology at the University of Utah College of Medicine, Moran Eye Center, Salt Lake City, Utah, Director of the Orange Grove Center for Corrective Eye Surgery in Tucson, Arizona and a board member of the American College of Eye Surgeons. Dr. Kershner has no financial or proprietary interest in any of the instruments, lenses or techniques described.
Legends to Slides:
1. Slide 1- Keep the cornea clear with one drop of 2.5% HPMC at the start of the case.
2. Slide 2-Hold the globe without undue discomfort to the patient with the Beaver disposable fixation ring.
3. Slide 3-Use the inkless marker to create two marks on the cornea for incision location and size.
4. Slide 4-The Beaver Clear Corneatome can create the ideal incision without the hassel.
5. Slide 5-Make the incision on the steepest meridian.
6. Slide 6-Make the clear cornea incision by following the corneal marks.
7. Slide 7-Use the one-step microcapsulorrhexer to create a round, central capsulorrhexis.
8. Slide 8-The one-piece injectable IOL goes through the clear corneal incision without enlarging.