Introduction
Cataract surgery is considered to be the premier surgery for ophthalmic surgeons. With declining interest in refractive surgery, ophthalmic surgeons are now faced with cataract surgery in the baby-boomer generation. Over the past several years, the impression given by many authors has been that cataract surgery is as good as it gets and that there would be little change to look forward to. Nothing could be further from the truth. Cataract surgery is on the verge of a major technological revolution. Looking at the information being disseminated from manufacturers, one can see that there is a major effort being placed in revolutionary ways of managing cataracts. This raises the question: "How will you be performing cataract surgery 5 years from now or even 2 years from now?"
Incision Size
The era of the 3-mm cataract incision is coming to an end. Over the last several years, we had the visceral impression that a 3-mm incision is small and that a 2.8-mm incision is miniscule. In light of the developments that have taken place, however, these incisions are large and their size has significant implications for the postoperative structure of the cornea, ranging from induced astigmatism to failure of the wound to remain sealed. We now are looking at cataract incisions that rival paracentesis sideport incisions; cataract incisions are moving into the arena of 1 mm to 1.5 mm.
Several years ago, Charles Kelman, MD, was asked if there was any significant implication to further reducing the size of the cataract incision. Dr. Kelman responded that the implications are staggering. He argued that as the wound size decreased to smaller than 2 mm, the possibilities for cataract surgery are immense. First, he indicated that the smaller incision would make it more difficult to introduce infectious contaminants, thereby facilitating in-office cataract surgery. I believe Dr. Kelman was correct and cataract surgery 5 years from now is going to be as different as cataract surgery was 20 years ago. A host of technologies will be developed from novel cataract extraction units to thin optics that will fit through 1.5-mm incisions. Not only will the eye remain more physiologic, but also, as stated by Dr. Kelman, cataract surgery will be conducted in office suites that resemble the familiar radial keratotomy suites or excimer laser suites.
New Device
I have been involved with the development of a new blade that has come into focus in the ophthalmic community over the last 4 years. This device is called the Fugo Blade in the United States and the Plasma Blade outside of the United States (Slide 1). The Fugo Blade is approved by the Food and Drug Administration for anterior capsulotomy in cataract surgery. The unit uses a disposable cutting tip, operates on flashlight-size rechargeable batteries and produces an incision that is unlike any other cutting device on the surgeon's table. The Fugo Blade ablates like a laser rather than cutting like a knife. It provides resistance-free incisions. The Fugo Blade operates much like a laser by focusing Planck electromagnetic quanta into an incising path using low power yet producing such high-energy density at the incising tip that one can actually visualize the electromagnetic field that exists around the cool, hair-thin cutting filament (Slide 2).
Over the past 2 years, many ophthalmologists have stated that this device is a diathermy unit. Categorically, the unit is unrelated to cautery or diathermy. First, the unit is powered by flashlight-size rechargeable batteries and has a total cut time of more than 1 hour in duration. Therefore, the amount of energy per unit of time, for example "per second," must be miniscule because the total amount of energy stored in the batteries is very low. Therefore, there is not enough power in the unit to act as a diathermy unit.
Furthermore, independent studies presented by David Apple, MD, at the 2002 and 2003 American Society of Cataract and Refractive Surgery (ASCRS) meetings show that the Fugo Blade is a unique cutting device producing ablation paths unrelated to diathermy. M. Edward Wilson Jr, MD, in conjunction with Rupal H. Triverdi, MD, and Garima Lal, MD, presented a video at the 2003 ASCRS meeting entitled "On Guard; Pulling, Cutting, or Burning Capsulotomies in Kids." In this video, Dr. Wilson and colleagues demonstrated that unlike the rough, blistered capsulotomy margin of diathermy, the Fugo Blade capsulotomy margin is relatively smooth and clean, comparable to a capsulorrhexis margin (Slide 3). The Fugo Blade margin is not as "perfectly" smooth as a capsulorrhexis margin because the capsulorrhexis tears along tissue planes, whereas the Fugo Blade causes an ablation path outside of tissue planes. If one examines an excimer laser ablation of cornea under high magnification, one will see minute irregularities due to ablation of tissue outside of tissue planes. This minute irregularity is due to differing energy absorption characteristics of adjacent tissues as well as other factors.
In 1991, Dr. Apple’s group wrote a paper on capsulotomy margins1 and listed the linear capsulotomy and the can-opener capsulotomy as "undesirable" capsulotomies, while listing capsulorrhexis and the postage-stamp capsulotomy as "desirable" capsulotomies (Slide 4). Furthermore, Dr. Apple’s 2003 ASCRS poster also studied the Fugo Blade postage-stamp margins.
The capsulorrhexis has a smooth margin, whereas the postage-stamp has 60 to 80 small waves on the capsulotomy margin. The postage-stamp is considered to be "desirable" because of the force vector configuration along the capsulotomy margin. The capsulorrhexis has force vectors that are "head to tail" (i.e., in a uniform direction), whereas the postage-stamp capsulotomy margin has force vectors that follow the wavy capsulotomy margin and are sometimes up and sometimes down. Therefore, the postage-stamp capsulotomy margin has force vectors along the margin, which are out of phase or not in a uniform direction. Basic physics tells us that force vectors that are in phase cause force vector amplification, whereas force vectors that are out of phase cause force vector cancellation (Slide 5). A simple analogy is that rowers rowing in synchrony produce a significant amount of force and thereby propel a boat. On the other hand, rowers who are rowing out of synch or phase produce little force and therefore the boat barely moves. The importance of this issue to the capsulotomy margin is significant because when one tears the capsulorrhexis margin, the amount of force that is directed into that tear is extremely large which is why a capsulorrhexis has a tendency to tear through the posterior capsule. On the other hand, this force vector cancellation of the postage-stamp capsulotomy means that a rim tear will create a very small total force vector directed into that rim tear and therefore the probability of that tear continuing into the posterior capsule is very low. That is one of the major differences between capsulorrhexis and the Fugo Blade capsulotomy.
Capsulorrhexis has been popular; however, Assia Ehmud, MD, and Dr. Apple indicated in their 1991 article that the "desirable" postage-stamp capsulotomy was technically difficult to create without ripping the margin in an unwanted fashion. It is important to understand that the Fugo Blade is designed to automatically ablate a waved postage stamp margin. At the 2002 ASCRS meeting, as well as in his poster at the 2003 ASCRS meeting, Dr. Apple demonstrated in micrographs that the Fugo Blade capsulotomy creates that waved configuration along the capsulotomy margin thereby producing a "desirable" form of capsulotomy margin (Slide 4). Combined with Dr. Wilson’s high-resolution micrographs of the edge of the wave margin, we see that although the margin is grossly waved, the edge of the Fugo Blade capsulotomy is almost as smooth as a capsulorrhexis (Slide 3).
Next, the Storm eye group took on the challenge of rim strength. They presented these data in their video entitled "On Guard: Pulling, Cutting, or Burning Capsulotomies in Kids" based on porcine models at the 2003 ASCRS meeting. Their findings can be summarized as follows. In young, healthy capsules, the Fugo Blade capsulotomy margin may be as strong as a capsulorrhexis. As the capsule ages, force vector amplification/cancellation results in an equilibration of the capsulorrhexis and Fugo Blade capsulotomy rim. As a matter of fact, in the older capsulotomies, the capsulorrhexis was suggested to be only 15% to 20% stronger than the Fugo Blade capsulotomy, but it is uncertain whether there is a significant difference between the two. This preliminary study will require further research and statistical analysis, but the data are fascinating. The data pool is not yet sufficient to provide definitive statistical significance.
Dr. Wilson’s group is at the forefront of capsulotomy biophysics and many await the outcome of his important research (Slide 6). However, from Dr. Wilson’s video, both the Fugo Blade capsulotomy and the capsulorrhexis appear to have substantially higher strength than the can-opener capsulotomy, vitrectorhexis or diathermy. The Fugo Blade also offers a unique technical capability to ophthalmic surgeons in that a surgeon easily can create a capsulotomy by ablating capsule in a resistance-free fashion thereby creating a capsulotomy of a desired target diameter. The surgeon is in control of the capsulotomy rather than merely reacting to the conditions of surgery. This has significant implications when one considers the biophysics of the capsulotomy and what causes a capsule rim to tear.
There has been insufficient discussion to date on the significance of the force that is placed on the internal surface of the anterior capsule rim. Thus, the question is raised: "What causes the capsule rim to tear?" Often, rim tears are caused by the total force that is placed on the interior surface of the anterior capsular rim by the cortex and nucleus pushing against the anterior capsular rim internal surface. Therefore, the total tearing force on the capsule rim is equal to the pressure of the lens cortex and nucleus times the total area of the anterior capsular rim.
Currently, the average capsulorrhexis is 5 mm. There is the issue of optic overlap and, as one gets further out toward the periphery, the chance of losing the capsulorrhexis to the equator increases. On the other hand, the Fugo Blade can easily make a 7-mm capsulotomy even in the situation of a small pupil where one is able to ablate under the iris. In this case, a small amount of viscoelastic lifts the iris off the anterior capsule and one can see the tenting effect of the cannula on the inner surface of the iris as one slowly moves along the capsule ablation path. This maneuver should be attempted by only experienced Fugo Blade surgeons who have 50 to 100 cases to their credit.
The advantages of producing a 7-mm capsulotomy with the Fugo Blade in an easy, quick and repeatable fashion are based on the biophysics of anterior capsular rim force. As stated above, the total force on the capsule rim is directly proportional to the total area of the anterior capsule rim. When one increases the capsulotomy from 5 mm to 7 mm, the capsule rim width decreases from 3 mm to 2 mm. Studies at our facility and at other facilities have shown that this is sufficient to protect zonular attachments. On the other hand, the increase from a 5-mm to 7-mm capsulotomy diameter reduces the total area of the anterior capsule rim by 46%. Therefore, since we are taught by biophysics that total force is directly proportional to the surface area of the anterior capsule rim, we see that the total force on a 7-mm rim is 46% less than a 5-mm capsulotomy rim. This is important to avoid rim tears.
Many surgeons avoid a large capsulorrhexis because of increased risk of tearing into the periphery of the capsule. Dr. Wilson’s data suggested an advantage in capsulorrhexis strength by 15% to 20% over Fugo Blade capsulotomy; however a 7-mm Fugo Blade capsulotomy has an effective strength advantage over a 5-mm capsulorrhexis of 26% (46% - 20% = 26%). For this reason, one is able to impale the cortex and nucleus with the phaco tip and pull the entire bulk through the anterior capsule rim with the 7-mm Fugo Blade capsulotomy. This is an efficient way to handle difficult cases such as small pupils. In this situation, I pull the nucleus and cortex bulk into the pupil and use this bulk as a pupil expander and slowly nibble away at the cortical nuclear bulk. This bulk holds the pupil open while keeping the posterior capsule away from the phaco tip. Also, phacoemulsification is performed substantially in the iris plane so that it is sufficiently far away from the endothelial cells so as to avoid damage to that structure.
We are beginning to see that the capsulotomy margin is not as "simple" as usually portrayed. Okihiro Nishi, MD, has shown that anterior capsular rim overlap of the optic and sharp optic edges alone may not provide a barrier for posterior capsule opacity (PCO) formation. Firm adhesion between the anterior capsule rim and the posterior capsule is crucial to reduce PCO.2 With a 2-mm to 2.5-mm anterior capsule rim, the rim adheres to the posterior capsule in 4 to 6 weeks thereby inhibiting PCO and also "locking" the haptic into place. Rather than purely protecting the posterior capsule from PCO, capsule overlap of the optic actually is the major cause for some of our most severe short-term and long-term complications that have developed since the implementation of capsulorrhexis. Some of these problems include capsular contraction syndrome, capsular retention syndrome, capsular phimosis, progressive zonular breakage and a progressive myopic shift. These complications are largely due to the progressive capsule fibrosis along a capsulorrhexis. This fibrosis is stimulated by the large force vectors (force vector amplification) that exist along the capsulorrhexis margin.
Another unique characteristic of the Fugo Blade has been presented by my research group as well as by Dr. Wilson and his associates. If a tear is introduced in the capsule rim, a small (2-mm to 3-mm) Fugo Blade ablation path can be made in front of and perpendicular to the capsule tear which will promptly stop the tear in capsule. Although off-label, if the posterior capsule becomes perforated, the Fugo Blade can be used to place a posterior capsular ablation path in the posterior capsule around the entire capsule tear. Therefore, one has an intact posterior capsule Fugo Blade capsulotomy. A small vitrectomy can be performed, if needed. One can proceed to place a posterior chamber IOL in the bag between the anterior capsule rim and the posterior capsule rim without fear of spontaneous tearing of the posterior capsule. Likewise, international surgeons routinely use the Fugo Blade to create bloodless iridotomies by merely tracing the ablation tip over the area in which the iridotomy is desired. The importance and versatility of this maneuver was highlighted by Daljit Singh, MD, who demonstrated in his 2003 ASCRS video presentation bloodless pupiloplasties that required several seconds to create. The lack of bleeding is not caused by cautery but by a new process called "autostasis."
Conclusion
An advantage of the Fugo Blade is that it allows surgeons to perform procedures heretofore considered technically impossible. The Fugo Blade allows the surgeon to control surgery. It is helpful in difficult cases. One such case was performed by Luther Fry, MD. Dr. Fry wrote, "The patient was an elderly gentleman with an old traumatic membranous cataract. The anterior capsule looked like leather and it would have been a challenge to cut with scissors. A cystotome would have been impossible, but the Fugo Blade worked like a charm."
Posted December 2003
References
- Assia EI, Apple DJ, Barden A, Tsai JC, Castaneda VE, Hoggatt JS. An experimental study comparing various anterior capsulectomy techniques. Arch Ophthalmology. 1991;109(5):642.
- Nishi O, Nishi K. Effect of the optic size of a single-piece acrylic intraocular lens on posterior capsule opacification. J Cataract Refract Surg. 2003;29(2):348-353.