Cataract Surgery Report

Does incision size matter?

Two key opinion leaders debate the pros and cons of microincision cataract surgery.

By Paul S. Koch, MD, and Robert J. Weinstock, MD

	About the Authors: Paul S. Koch, MD, is editor emeritus of Ophthalmology Management and medical director of Koch Eye Associates in Warwick, R.I.
	Robert J. Weinstock, MD, is a cataract and refractive surgeon The Eye Institute of West Florida, Largo.

Micro-incision cataract surgery — known as MICS — has made inroads into ophthalmic surgical suites, but the approach isn’t without controversy. Advocates say that because MICS uses smaller incisions than the traditional technique, it causes less trauma to the eye, reduces the likelihood of postoperative astigmatism and carries fewer risks of dry eye and other postoperative problems. The technique and equipment MICS requires are the same as the conventional approach, so the learning curve is virtually nonexistent.

Those who take the opposite view note that few IOLs are suitable for MICS, the smaller incision is more prone to uneven edges and irregular healing, and may actually restrict a surgeon’s ability to manipulate instruments inside the capsule, and the improvement over the conventional approach is too incremental to merit broad acceptance.

Diving deeper into the debate are two well-respected surgeons: Paul Koch, MD, editor emeritus of Ophthalmology Management and medical director of Koch Eye Associates in Warwick, R.I., taking the position that MICS is not ready for prime time; and Robert J. Weinstock, MD, a cataract and refractive surgeon at the Eye Institute of West Florida in Largo, Fla., arguing for MICS.

MICS DEFINED

Micro-incision cataract surgery utilizes incisions ranging in size from 1.8 mm to 2.4 mm vs. 2.7 mm to 3.2 mm for traditional surgery. The smaller incision can accommodate phaco tips as small as 1.8 mm in diameter. Two types of MICS exist.

Coaxial, or C-MICS

This approach most closely resembles traditional cataract surgery. Incision size can range from 2 mm to 2.2 mm. The phaco tip enters through a primary incision. A second incision, smaller than 2 mm, accommodates the “chopper” tool. High vacuum levels are possible with advanced fluidics, and power modulation generates less heat than in conventional phacoemulsification.

Bimanual, or B-MICS

This more advanced approach separates irrigation from phacoemulsification and aspiration, allowing for superior control of fluid dynamics, advocates say. A steady flow of irrigation into the anterior chamber allows for highly controlled manipulation of the phaco handpiece and nuclear particles.

The sleeveless irrigating chopper acts as an additional instrument inside the eye by directing particles to the phaco tip, whereas in coaxial surgery the irrigation tends to repel lens material away from the phaco tip. B-MICS is faster, uses less phaco energy, causes less endothelial cell loss and less postoperative inflammation and promotes faster healing and visual recovery, according to its proponents.

ENOUGH IOL OPTIONS?

Q Do surgeons have enough IOL options to broadly embrace MICS?

Dr. Koch: I’m not sure how many lenses can be used with MICS. I know there are a handful, including the Akreos from Bausch + Lomb Surgical (Aliso Viejo, Calif.). But with the traditional phaco incision, you have the freedom to use any IOL you want.

Dr. Weinstock: We do not have a lot of lenses right now can go through a 2.2-mm incision. With a good wound-assisted injection technique, the AcrySof (Alcon, Forth Worth, Texas) can go through that incision. The Akreos MICS platform can actually easily go through a 2.2-mm incision, and with wound assist it can actually go through a 1.8-mm incision. So the arsenal of lenses available to go through these smaller wounds is already beginning to expand and will continue to expand.

WOUND CLOSURE

Q How can wound management during IOL injection influence outcomes?

Dr. Weinstock: Some lenses, such as the Crystalens (B + L Surgical) and the multifocal intraocular lenses require a slightly larger incision, but there is some merit in doing MICS and then enlarging the wound for the IOL at the end of the procedure. With this approach, you are operating through a smaller wound with a more closed and sealed chamber and more stability in the chamber during the most critical parts of the surgery, when complications often occur.

In my experience, that adds an element of increased safety and can reduce complications by having the smaller, tighter wound where the fluid dynamics are more predictable and under the surgeon’s control.

Dr. Koch: When you make an incision with the blade, you have perfectly smooth and sharp edges to the incision, and it seals very nicely. If someone is tempted to squeeze or force in an injector through an incision that is too small, to fit it into the eye, the edges of the incision necessarily have to rip. This will create an irregular contour, and that will damage the water tightness of the incision. We’re more likely to get a nice seal on the incision if we don’t have to damage it while injecting the lens.

PHACO BEHAVIOR

Q How does phaco behavior differ between conventional cataract surgery and MICS?

Dr. Weinstock: I use exclusively bimanual sleeveless 19-gauge instruments through a pair of trapezoidal 1.4/1.6 incisions 80º apart. Howard Fine taught me this incredibly refined, elegant and controlled way of removing cataracts a decade ago.

This setup is the right balance of efficiency, chamber stability and safety for me. And now, with the Akreos MICS, I can use a wound-assisted injection technique and operate through these small wound start to finish.

I have compared my B-MICS to C-MICS phaco time, case time, day one vision and complication rate. B-MICS outperforms in all areas in my hands.

Dr. Koch: My preference is to have as little resistance as possible when comes to removing lens fragments from the eye. I use a 19-gauge needle with a 0.9-mm central opening, and I am able to emulsify the nucleus to pieces that will fit out through that needle. If I had a smaller needle, I would have to emulsify a little more. We’re talking very small quantities either way.

In terms of surgical efficiency, with the larger sleeve I have the ability to put in more fluid if I want to flush quicker and the ability to use a wider needle, so I can aspirate out quicker. I’m happy with that balance that we have.

INCISION SIZE

Q How does incision size influence outcomes in cataract surgery?

Dr. Koch: With a properly made incision, either incision will close perfectly because for all practical purposes, they are the same size. We’re only talking a couple microns difference in size. We saw a big difference when we went from 12-mm to 6-mm incisions and 6-mm to 3-mm, but once you’re at 3,000 μm or 2,400 μm, they really are, for all practical purposes, the same size incision. If you make it properly, it’s going to seal up just beautifully. I don’t think that the proponents of MICS can tout an advantage on the sealing of the incision, assuming the surgeon using either technique is making a good one in the first place.

I’ve assisted doing people doing MICS, and each time failed to see how it is significantly better than surgery with a 3-mm incision. The ability to flush out material is still the key to efficient surgery.

Having the smaller sleeve means less inflow, and the smaller needle means less outflow, but you do not necessarily have less resistance. A smaller incision also restricts how the phaco tip moves through incision to the left and right.

With the 3-mm incision, we are more likely to have unrestricted inflow, and the larger phaco tip is more efficient in getting nuclear pieces out of the eye. The larger incision also makes it easier to move the phaco tip to the left and right within the eye.

Dr. Weinstock: The larger the wound, the more corneal nerves you cut, which can cause dry eye and postoperative dissatisfaction and complications for the patient. In theory, the larger the wound, the higher the risk of endophthalmitis. Although that’s rare today, it is still out there, and endophthalmitis is a devastating event for the patient and obviously for the surgeon.

In addition, we see so many patients these days with floppy iris syndrome, and the smaller wound does a great job of reducing iris prolapse compared to a larger wound. Smaller wounds also create less leakage during the case and more chamber stability in my opinion.

LEARNING CURVE

Q Does MICS require a steep learning curve?

Dr. Weinstock: The learning curve is almost completely transparent and simple — especially in C-MICS if the surgeon does his or her diligence in getting the instrumentation and the phaco machine set on the right mode with the right settings. It is nearly a seamless transition.

B-MICS is a little more involved because you’re learning to use your nondominant hand even more. But again, the surgeons that I’ve trained to do B-MICS have never turned back to do coaxial phaco once they get the hang of it.

They immediately recognize the benefits of separating the irrigation from the aspiration and the phaco and the increased control and predictability they experience inside the eye.

Dr. Koch: No, coaxial MICS does not require a learning curve. It’s the same technique with a small incision and smaller tools. I don’t think there’s a learning curve at all. There is a learning curve if you want to use bimanual MICS.

WHAT LIES AHEAD

Q What’s the next step in the evolution of cataract surgery?

Dr. Koch: If we can get to a 1.5-mm incision, then we have another revolution in cataract surgery. I’ll give you that right now. But we can’t do that with the lenses we have now because they’re too thick, or they have too much bulk.

Although we already use IOLs with refractive indices that allow them to be made thin — thin enough to be rolled up into a micro-injector that fits into a small incision — someday, we will be able to marry everything together, so the patient has what is essentially a needle stick in the eye rather than an incision.

It is only a matter of polymer chemistry and engineering that’s keeping us from getting there. So whether it’s the engineering of a very, very thin and rollable lens or whether it’s the chemistry of a lens of a certain refractive index that will be optically pure and yet have very little bulk, I believe that’s where the future of the next incision revolution lies.

Dr. Weinstock: The logical next step here is to automate the surgery, like we’re doing with lasers, and reduce the risk of complications, such as capsular tear or damage to the iris or damage to the zonules or the cornea, as well as decreasing problems such as surgically induced astigmatism, which becomes significant; the larger the wound is, the more surgically induced astigmatism there is.

The next level eventually — maybe its two or three levels from now — needs to be a combined energy effort across our industry to push toward two separate 1-mm incisions, one for irrigation and one for aspiration; complete laser disintegration of the lens, requiring minimal need for phaco; and then injecting some type of soft jelly-like biocompatible material that hardens or can be adjusted to the appropriate refractive index and power once it’s inside the eye. Then, we would truly be approaching the safest, least invasive and the most precise procedure possible.

When that’s going to be, I don’t know, but I think we need to set our sights on that and incrementally move in that direction. Staying with the 3-mm incision ad infinitum is clearly not going to achieve that goal.

ClOSING ARGUMENTS

Q So is MICS ready for prime time?

Dr. Weinstock: I bet the same question was asked when we went from intracapsular to extracapsular surgery or when it went from extracapsular to phaco.

What defines prime time? In my mind, it’s defined by when the technology has matured enough that the machines and handpieces and instrumentation have been modified or developed or engineered to the point that they are safe for the everyday surgeon to use.

I truly believe, whether it’s C-MICS or B-MICS, the phaco machines we have today are highly evolved to where, if the surgeon wants to make the transition to smaller-incision surgery, the technology is there to do so. We’re not talking about entry-level, first-generation handpieces or phacoemulsification software. We really have the tools we need to do this successfully without any risk.

For that reason alone, I believe MICS is ready for prime time, and the fact that we do have lenses that can go through these wounds makes it so in a majority of cases, you truly can operate start to finish through a 2.2-mm or 1.8-mm wound — the latter if you’re using the Akreos MICS with a wound-assist technique.

Dr. Koch: Again, my position is that C-MICS, for all practical purposes, is the same thing as conventional surgery, because reducing the incision only 600 μm, which is 300 μm to the left and 300 μm to the right of the existing incision, is a tiny, tiny tolerance.

I have not been convinced that it offers any advantage over what I’m doing now, I think MICS may actually restrict my ability to remove a cataract through a large-bore needle. OM