January 2002 marked the 12th anniversary of the sutureless operation. Since that surgical leap forward, incisions have become progressively smaller in accordance with continuing advances in intraocular-lens technology. These changes in the field have rendered obsolete many arguments and achievements of the past. The issues of continued relevance today are those of wound geometry and location. This article will look at where we stand and where our steps are leading.

Geometry
In the mid-1990s, debate about the ideal geometry of the cataract incision led me to perform numerous cadaver studies.^1,2  What I found, essentially, was that a square shape and the presence of at least 1.5 mm of corneal tissue created a secure wound that couldn’t leak under any type of internal or external pressure, even pinpoint pressure behind the incision.

Along the same lines, Rupert Menapace, MD, of Vienna, Austria, conducted topographic studies comparing the astigmatism induced by the different types of incisions at one week and three months postop.³  He found that the square incision was most stable and induced the least amount of astigmatism.

The issue of ideal wound geometry was one of contention, because, of course, older corneal incisions were about 4 mm in width by 1.5 mm in depth—anything but square—and they leaked even under the pressure of only a finger. Many physicians, such as myself, did not embrace corneal incisions specifically because of their rectangular configuration.

Today’s cataract incisions, by contrast, have a very narrow profile. Surgeons are able to extract the natural lens and insert an IOL through incisions of less

A wound’s location impacts its rate of healing. Because they are located much closer to the vascular supply, limbal incisions heal quicker than those made in true cornea.

Harry B. Grabow, MD

than 3 mm. Because the tunnel length now approximates the width, the incisions are nearly square and, as such, inherently stable mechanically. It’s important to realize, however, that leakage is not an all or none phenomenon. Simply put, the more square the wound, the better its integrity and the less likely it is to leak. That does not mean that only square incisions don’t leak, however.

 • Construction. Orangeburg, N.Y., surgeon David Langerman made the valuable contribution to the field of his hinged incision, which added stability to the rectangular wounds of the past. If the eye were pushed on, the extra amount of groove would take up the external pressure without transmitting it to the floor of the tunnel.

As cataract incisions narrowed, wound construction became less important. Nevertheless, grooving continued to be advantageous before more recent improvements of cataract knives. Older style blades often produced an

Figure 1. Whether limbal or corneal, the square wounds do not leak, even with pinpoint pressure of up to 525 lb/in2. The four incisions on the left are all square. That on the far left is a limbal incision, while the other three are corneal. By contrast, the incision on the far right leaks with the application of minimal pinpoint pressure if the pressure is low. Just going to a higher pressure increases the wound’s resistance to leakage by a factor of 8 or 9. Contrarily, if you lengthen the wound by 0.5 mm, shown to the left, resistance increases by a factor of 8 with the same pressure. Lengthening the incision so that it measures 3.2 mm x 3.2 mm, meanwhile, results in an increase in resistance by a factor of 40 compared to the 3.2 mm x 2.0 mm incision.

irregular configuration on the external part of the wound, and grooving first enabled the surgeon to be sure where the incision began. Today’s blades don’t create irregular configurations, which allows us to forego grooving and make a single pass.

 • Knives. One potential issue for continued debate is whether a surgeon should opt for diamond or steel knives. Technological advancements in steel knives have created better designs and an excellent degree of sharpness. The decision, therefore, is a matter of surgical setting and preference.

The advantages of the diamond blade are that incisions created with it are reproducible and, when well-maintained, it will hold up to much use, which makes it more cost efficient than steel. This economy is lost if the blade is shared by multiple surgeons, however, because handling by myriad people makes it more prone to damage.

Surgeons who prefer steel knives are those, such as myself, who like to feel the resistance of a steel blade when making an incision, something diamond blades don’t provide. Steel keratome blades are the best choice for a surgeon who appreciates tactile tension and feedback.

 • Treating astigmatism. Since current cataract incisions are so small, they’re essentially astigmatism neutral. Some surgeons will make larger incisions on the axis of astigmatism in order to allow the wound to slide or shift and thereby offset the preexisting astigmatism. Most surgeons rely instead on limbal relaxing incisions to treat preexisting astigmatism. Other options include secondary procedures like LASIK or implant technology involving toric IOLs. Because the smaller incisions are astigmatically neutral, the surgeon may place the axis of the toric lens in the same direction as the axis of astigmatism.

I personally use a temporal approach and make a sub-3-mm incision. If I want to affect the level of astigmatism, I’ll do so intraoperatively via a toric lens, or I’ll deal with it postop.

Location
Cataract surgeons have long argued the merits of the temporal limbal vs. the clear corneal incision and so forth. Whatever wound location we advocate, it’s important first to be sure that all the parties involved are speaking from the same playbook.

• Defining clear cornea. One of the difficulties that arises when ophthalmologists debate the ideal place to make the cataract incision is one of semantics. The term “clear cornea” is a cute cliché that’s become ingrained in the minds of most cataract surgeons. The problem is that some physicians base their use of the term on a slit lamp definition, when the identification of the limbus and cornea actually depends on histologic definitions. David Apple, MD, of Charleston, S.C., strongly emphasizes the importance of this differentiation, and I wholeheartedly agree with him.

Histologically, the limbus begins where Bowman’s membrane stops in the peripheral cornea. Unless there’s a pathologic condition like pannus, the small blood vessels coming from the conjunctiva and extending into the cornea stop short of Bowman’s membrane. If you cut through these terminal vessels of the vascular arcade and the conjunctiva, you are still in the anterior limbus, even though, from a slit lamp appearance, you’re into the cornea.

The shorthand terminology we use for convenience isn’t important, in the end, provided we—and any audience we’re addressing—understand where we are anatomically. 

 • Healing. The significance of wound location is its impact on the rate of wound healing. In a study designed specifically to determine how fast incisions heal, I found that limbal incisions heal faster than corneal ones.⁴  Specifically, when the incision was made even at the most anterior portion of the limbus, the wound healed completely in seven days. Incisions made in true cornea, however, took up to 60 days to heal.

Because limbal incisions are so much closer to the vascular supply, they heal more quickly via a fibroblastic response. In the true corneal incision, wound healing entails metaplasia of the keratocytes into fibroblasts, which seals the incision in 30 to 60 days.

The downside of operating in the anterior limbus is potential conjunctival ballooning. This complication may be avoided by careful surgical planning and intraoperative care, since it derives from a definite source: the sub-Tenon’s space. If the surgeon cuts into it, the fluid that comes out of the incision will get under the space and cause the conjunctiva to balloon. There’s an area of the limbus that does not have a sub-Tenon’s space, and that is, therefore, the ideal place to make the cataract incision.

Even so, problems can still arise as the surgeon passes the keratome blade into the incision. Friction from the bottom part of the blade tends to drag some of the posterior conjunctiva into the incision, where it’s easily nicked by the shoulder of the blade. The result is a tiny buttonhole in the conjunctiva. It acts almost like a peripheral retinal hole that the fluid goes through, which results in ballooning. Preventing conjunctival drag is, therefore, important. If you do happen to drag and nick the conjunctiva and ballooning begins, you can remedy the problem by using a very small pair of Vannas scissors to extend the buttonhole into a mini-peritomy.

 • Endophthalmitis. The idea that clear corneal incisions may result in a higher incidence of endophthalmitis has been with us since Eugene, Ore., surgeon I. Howard Fine introduced the incision during a 1992 presentation at the annual meeting of the American Society of Cataract and Refractive Surgery. To date, information has been anecdotal, although Samuel Masket, MD, of West Hills, Calif., made a valiant effort to verify these reports scientifically. During a retrospective study of the issue, he was unable to prove the matter one way or the other via statistical analysis, however. Anecdotally, a lot of surgeons who

Figure 3. In the same feline study, the true corneal incision had not healed at 7 days postop (left), while a limbal incision on the fellow eye at 7 days postop had (right). In the latter image, note the line of fibroblasts between the two areas of cut tissue.
Paul H. Ernest, MD

used clear corneal incisions have reverted to starting their incisions slightly more posteriorly in the limbal area, because they truly feel that this location results in a lesser incidence of endophthalmitis.

Obviously, infection is an issue, especially when considering whether to seal a wound in seven or 60 days. Most infections occur at the time of surgery upon the introduction into the eye of a contaminant from the flora of the conjunctiva. The real question is whether these infections described with clear corneal incisions come from contaminants that are introduced postoperatively, as many suspect, based on how the wound behaves. There’s no way to prove this theory.

The Future Looks Small
In many respects, it’s the cataract procedure of tomorrow that holds the greatest interest for our subspecialty. The new emphasis in the field rests on the 1-mm cataract incision, and I anticipate that surgeons will be operating through incisions sized, at most, 1.0-1.5 mm within the next few years. At that point, the topic of incisions will be moot, because they’ll be essentially square and excellently stable.

It is the manufacturers that are making the 1.0-mm incision seem a soon-to-be-realized reality. They are busily making exciting strides in phaco technology and working with a variety of modalities, including laser phaco and the infusion of hot water. Other companies are splitting the standard phaco handpiece in two to create bimanual phaco. We already do bimanual vitrectomies and irrigation/aspiration, so this idea shouldn’t seem outlandish. The technology uses intermittent bursts of phaco so that the needle never reaches a high temperature.

Advances in phaco technology will spur on research in implant technology. We will need an IOL that can go through the smaller incisions, and they’re already working on such lenses in Europe. One sort has an extremely thin profile, and another is desiccated; both types are then rolled up into tiny scrolls for insertion through incisions of about 1 mm. The stability of these lenses has yet to be proven, however, and we’ll want to be sure that, when the capsular bag retracts, they aren’t so thin that they contract and become distorted.

All of these technological changes will entail an alteration of how we do the capsulorhexis, since we’ll no longer be able to use our current instrumentation. Surgeons won’t trade in technology that gives their patients a high degree of satisfaction, however, just to save a millimeter on wound size. First, we’ll need proven benefits. 

Dr. Ernest pioneered the current no-stitch technique in cataract surgery that is widely used today. He is actively involved in several areas of ophthalmic research, has written dozens of articles and papers, and is a much sought after lecturer, both nationally and internationally.

1. Ernest PH, Fenzl R, Lavery KT, Sensoli A. Relative stability of clear corneal incisions in a cadaver eye model. J Cataract Refract Surg 1995;21:1:39-42.
2. Ernest PH, Lavery KT, Kiessling LA. Relative Strength of scleral corneal and clear corneal incisions constructed in cadaver eyes. J Cataract Refract Surg 1994;20:6:626-9.
3. Pfleger T, Skorpik C, Menapace R, Scholz U, Webhaupt H, Zehetmayer M. Long-term course of induced astigmatism after clear corneal incision cataract surgery. J Cataract Refract Surg 1996;22:1:72-7.
4. Ernest P, Tipperman R, Eagle R, Kardasis C, Lavery K, Sensoli A, Rhem M. Is there a difference in incision healing based on location? J Cataract Refract Surg 1998;24:4:482-6.

For Further Reading
Ernest PH, Fine IH, Fishkind WJ. Incision Wound Healing. In: Buzard KA, Friedlander MH, Febbraro J, eds. The Blue Line Incision and Refractive Phacoemulsification. Thorofare: Slack 2000, 15-52.