As you know, the clear corneal procedure is now the choice of many cataract surgeons. Last month, we looked at ways to incorporate it into your surgical routine, and how to improve your technique.
Here, we'll take a closer look at one aspect of this cataract surgery choice -- the temporal clear corneal incision. We asked leading surgeons to tell us why (and when) they choose the temporal location, to share their temporal incision approaches, and to offer some strategies for adjusting your OR procedure.
Location, location, location
After I. Howard Fine, M.D., presented his clear corneal incision to the American Society of Cataract and Refractive Surgery in 1992 (emphasizing the temporal location), it became apparent to many surgeons that the temporal location provided the most advantages.
Shortly thereafter, Charles H. Williamson, M.D., of Baton Rogue, La., became the first surgeon to perform temporal clear cornea using topical anesthesia. He offered the first seminar for surgeons touting the temporal location in August 1992.
"There are several reasons for doing the surgery temporally," Dr. Williamson says. "When the patient is undergoing surgery under topical anesthesia, they're asked to fixate on the microscope light. If you're temporal, the patient can look directly at the light. If you're doing it superiorly, the patient has to look down, and there's nothing to fixate on."
Drs. Fine and Williamson list other reasons they've chosen the temporal location:
� Temporally, you have better exposure to the surgical limbus, even in deep-set eyes.
In 1992 incisions were
larger. Dr. Williamson says it was his belief that because the incision was essentially perpendicular to the direction of lid blink, there would be less wound gaping and leaking.
� The end of Bowman's membrane is elliptical, meaning that the temporal cornea is farther from the visual axis. As a result, any surgically-induced astigmatism caused by the surgery will be minimized.
Harry Grabow, M.D., started superiorly with clear cornea in 1992, but switched to temporal for several reasons.
"Originally I started with a 3.2 mm phaco and foldable incision, but after fewer than 20 cases I discovered that I could induce as much as three diopters of against-the-rule astigmatism with that incision," Dr. Grabow says. "Later on, when I did cell counts on those patients, I found a central corneal cell loss of around 14% in some cases.
"I quickly moved to the temporal location, and I found that the induction of astigmatism was half that induced at the superior location. The loss of endothelial cells was also half that of the superior location."
Clear corneal pioneer Dr. Fine agrees. "The temporal location is the furthest distance from the visual axis on the cornea. The central axis is nasally placed. As a result, the flattening that occurs at the incision site is less likely to be transmitted to the visual axis from the temporal location than from any other.
"The temporal location also provides much easier access to the temporal periphery than any other area in the cornea," he continues, "and that's because the angle of the lid sits beneath it. So in deep-set eyes or prominent brows we don't have to use bridal sutures, and we don't have to turn the eye down. We don't have to cut or touch a needle through the conjunctiva.
"In addition, it's much easier to move instruments in and out of the eye."
Dr. Fine adds that along with the temporal location being the most astigmatically-neutral and ergonomically easiet for the surgeon, there's an even bigger benefit. "The location of the lateral canthal angle lets the eye drain naturally," he says. "That's the greatest advantage. With other incisions, fluids can pool in the conjunctiva. With the temporal incisions, fluids drain away -- there's no pooling."
Incision shape and plane
When Dr. Fine introduced clear cornea, most cataract incisions were larger. With the introduction of injectable intraocular lenses (IOLs), surgeons were able to make much smaller incisions. Today, there are three prominent temporal clear corneal approaches.
"We learned from the studies of Paul Ernest and others, the closer we can make the clear corneal incision to a square in dimension, the stronger the incision will be postoperatively," Dr. Grabow explains. "However, most surgeons make a self-sealing incision that's physiologically stable.
"I prefer to make a trapezoid incision that has a smaller internal opening and a larger external opening. That type was originally designed by Dr. Williamson. It gives me a safer internal valve for sealing the incision and allows increased maneuverability of the instruments.
"The incision can be made as a single-plane or as a two-plane incision. The two-plane incision involves a vertical groove incision that's parallel to the limbus and extends slightly beyond the margins of the second-plane incision, which will enter the anterior chamber. The depth of that groove can be 300, 400, or 600 microns.
"The 600 micron depth was recommended by David Langerman for separation of compression forces postopera- tively," he adds. The Langerman hinge incision was designed to be more resistant to eye rubbing.
"In 80% to 90% of cases, I use a single-plane incision," Dr. Grabow continues. "This is because I don't intend to use that incision to alter astigmatism.
"If the patient has against-the-rule astigmatism, I'll make a limbal relaxing incision (LRI) of 550 microns for the appropriate arc length, and possibly couple it with an additional LRI or astigmatic keratotomy (AK) at the opposite meridian. I'll use the proximal LRI as the vertical groove component of the two-plane phaco incision.
"At the conclusion of all cases I hydrate the stroma with balanced salt solution."
Using a groove
Surgeons may choose different approaches for different patients, but they usually favor one type. Dr. Williamson prefers to use the groove, or step, incision.
"People talked about the two-step incision, or groove incision, and said the incisions were stronger. We started making a hinge for the same reason," he says. "We found that once the wounds got below 3 mm, it didn't really matter which of the three incision types you made: a single, a grooved incision (or a step), or the hinge. The wounds didn't leak."
With that said, Dr. Williamson explains why he still favors the step.
"The real reason to make a step incision is that the beveled incision made the corneal edge of the incision so thin it would sometimes fray and cause a problem. That thin little edge would get chewed up. So what I did by making this incision or groove into the cornea was make the edge much thicker. That was my reason for making the groove -- not to reduce wound leakage.
"I also think it's the easiest incision to learn. The doctor can make a groove and then make the tunnel incision."
Dr. Williamson explains his technique: "I make a 2.5 mm groove into the clear cornea just ahead of the conjunctiva. I use a Diamatrix step knife with a guarded blade to make a groove 300 to 400 microns deep. I then extend the blade and do a side stab incision to the left, because I'm right-handed. I inject a viscoelastic through the side-step incision and fill the anterior chamber, replacing the aqueous as I inject. I use a 2.5 to 2.9 mm Diamatrix trap blade diamond to create a trapezoidal corneal tunnel about 1.75 mm in length."
Roger F. Steinert, M.D., also chooses the groove, or step, temporal incision.
"I use a Rhein diamond keratome that has a step advancement. First I make a 300 micron-deep groove. Then I advance the blade fully, and use it to make a 2.8 mm clear corneal tunnel, with a length of 1.75 mm before it enters the anterior chamber," Dr. Steinert says.
"The reason for the groove is that it gives strength to the external corners of the incision. Especially for beginning surgeons, this step helps avoid tearing of the external corners during surgical maneuvers that stress the incision," Dr. Steinert explains. "In some cases, I also use a single-plane incision. I get the same wound integrity either way."
Tips for beginners
If you're thinking of incorporating temporal clear cornea into your surgical routine, Dr. Steinert suggests:
� Insure strong incisions. Do a groove to ensure that the external corners of the incision are stronger.
� Finish as phaco. If you can't complete the case as phaco and you have to convert to extracapsular cataract extraction, go to a superior site and make a conventional corneoscleral incision. Otherwise, high astigmatism is likely from the wide corneal wound.
Be comfortable. The enhanced visualization and maneuverability from
temporal incisions is vastly superior to going over the brow for superior
incisions. Once you adapt, you'll love it!
The biggest obstacle is being comfortable during the surgery. A few surgeons sit superiorly and use instruments both nasally and temporally, which Dr. Steinert says doesn't work well for his technique. He has a Stryker OR bed that lets him sit to the side and allows good access for his legs.
If necessary, you can adjust the patient's position. This usually means moving the patient superiorly and/or toward you. The oculars of the microscope may need to be tilted to full horizontal. If you're short, you can tilt the whole microscope as well to create adequate comfort.
� The opposite eye. When operating on the eye that is opposite your dominant hand, the incision can be skewed superotemporally. But don't do a clear cornea incision between 11 and 1 o'clock, because the induced astigmatism may be considerable. Astigmatism shifts are minimal from incisions made between 8 and 10 o'clock.
When you move to the temporal location, it's also important to make sure you can fit your legs under the table and still reach the microscope pedal and phaco machine pedal, Dr. Grabow says. He found it helpful to change the objective lens on the microscope to a shorter working distance, so that he could raise the table a little higher to allow more room for his legs.
Dr. Grabow also suggests that you tilt the patient's head slightly toward you and angle the microscope body tube slightly toward you. This keeps the microscope's body tube perpendicular to the plane of the iris, while allowing you to sit up straight.
"The surgeon will also notice that he can no longer rest his hands on his patient's forehead for stability," Dr. Grabow says. "I recommend gentle placement of the hands on the temporal area. Excessive pressure will cause the head to rotate away from the surgeon, a phenomenon prevented by taping the head to the table."
Dr. Grabow adds that it's important to remember that your hands will be held more closely together for temporal surgery than they usually are during superior surgery.
Finding your spot
All the surgeons who've outlined the merits of the temporal clear corneal incision above agree that it may take you some time to adapt to working from the different location. But they also agree that after the transition, this approach will become ergonomically easier than other approaches.
Considering the benefits both you and your patients will reap, this is definitely an incision worth trying.
When the Temporal Location Isn't Appropriate
While a temporal clear cornea incision is the right location for many cataract patients, in some cases, you may need to look elsewhere.
Roger F. Steinert, M.D., says he chooses another location:
� when a patient has peripheral degeneration of the cornea
when enlargement of
the incision is needed (such as when inserting a non-
� when a combined glaucoma procedure is planned.
Charles H. Williamson, M.D., adds that when you want to induce astigmatism you should use a different approach. Also, for peripheral corneal disease such as corneal melt, a scleral incision is more appropriate.
What About Refractive Surgery Patients?
How does refractive surgery affect your temporal location preference? Some surgeons say it shouldn't, while others recommend some precautionary measures to take so that laser-assisted in situ keratomileusis (LASIK), photorefractive keratectomy (PRK) or radial keratotomy (RK) patients don't become hyperopic after cataract surgery.
"It's important to note that with RK you have to modify the current IOL calculations, and you have to have a corneal topographer to calculate the true keratometric reading, rather than using a manual keratometer," says Charles H. Williamson, M.D. "Otherwise your result will be too hyperopic."
"I would consider using a superior scleral pocket incision in eyes that have had corneal refractive surgery such as LASIK or RK," says Harry Grabow, M.D. "I know there are some surgeons who've been successful with temporal clear corneal incisions in eyes that have had RK. However, there have also been cases reported where a temporal clear corneal incision was used in an eye with previous RK in which the RK incisions split open and required significant suturing in order to stabilize the cornea."