9.3Corneal Endothelium and Other Safety Issues

H. Burkhard Dick1

Core Messages

ßMany surgeons are still apprehensive to convert their surgical technique for fear of increased

complications, including endothelial cell loss, intraocular pressure, and endophthalmitis. The density of the nucleus affects endothelial cell loss because of the number of small, hard fragments in the anterior chamber.

ßWhen MICS is performed correctly, risk of these complications is minimized.

ßIt is important to learn to avoid complications during MICS, such as endothelial cell loss and

elevated intraocular pressure, as well as manage these complications when they arise.

ßEndothelial cell loss was only weakly associated with the average of phaco power used in

foot position three.

ßUsing power modulation as well as pulse/ hyperpulse and burst/hyperburst should not

only reduce the loss of endothelial cells but also provide quicker visual recovery for the patient.

ßThe longer standard coaxial as well as microcoaxial phacoemulsification lasts and the more

power that is used, the greater is the endothelial cell loss.

ßThe correlation between endothelial cell loss and total phacoemulsification energy and length

of the procedure is weak.

ßAdditional risk factors for an increase in endothelial cell loss include operating on harder cata-

racts, size of the cataractous nucleus, infusion volume, and total phaco energy.

ßAccepting the challenge to convert comes with many rewards, including less wound-related

complications and quicker visual recovery.

1The author has no financial interest in any materials or products mentioned in the article.

H. B. Dick

Center for Vision Science, Ruhr University Eye Hospital, In der Schornau 23-25, 44892 Bochum, Germany e-mail: burkhard.dick@kk-bochum.de

The evolution of cataract surgery in the past few years has been bountiful. In addition to innovative technologies, new and enhanced surgical techniques and smaller incision sizes have increased the development of cataract surgery. Patients are enjoying improved results and faster visual recovery. However, the threat of intraand postoperative complications, including endothelial cell loss, is enough for some surgeons to shy away from tackling a small-incision technique.

Most complications are avoidable, and the advantages of minimizing cataract surgery incisions to sub-2 mm outweigh the potential complications associated with it. Although a learning curve can be expected for those surgeons who have not previously used smallincision cataract surgery, it is relatively short and may easily be overcome by paying close attention to details and quickly learning to manage complications or difficulties that arise.

When discussing incision lengths, I like to use the following terms to distinguish the size of the incision:

•Long-incision cataract surgery. This term coincides with extraor intracapsular cataract extraction via a 10-mm incision.

•Small-incision cataract surgery. This term is meant for phacoemulsification with a PMMA IOL with a 6-mm incision.

•Mini-incision cataract surgery. When a foldable IOL is inserted through a 3-mm incision, I refer to it as mini-incision cataract surgery.

•Microincision cataract surgery. Any procedure employing a 1.5-mm or smaller incision is referred to as microincision cataract surgery (MICS).

For the purpose of this article, we will be discussing mini-incision and microincision surgery. Although the size of the incision is likely to vary depending on the surgeon’s preference, such as his choice of instrumentation, and skill level, any decrease in incision size may come with the benefits of: decreased postoperative intraocular inflammation, less wound-related complications and surgically induced astigmatism, and shortersurgicalandrehabilitationtime[1].Additionally, biaxial and coaxial MICS allows the surgeon to vary the power during the surgery, thus decreasing the necessary amount of ultrasound energy, creating a stable anterior chamber, and promoting clearer corneas and faster visual rehabilitation [2].

Reducing the incision size during cataract surgery has recently become more common worldwide; however, the techniques of MICS are still evolving. Many surgeons debate the safest and easiest options for MICS

or mini-incision cataract surgery. While some surgeons use unsleeved phaco tips through two 1.5-mm incisions and enlarging the incision size to 2.8 mm for IOL insertion (i.e., biaxial MICS), others use sleeved phaco tips through larger, 2-mm incisions (i.e., coaxial phacoemulsification). The controversy regarding which of these two methods is better will continue, just as some surgeons will continue to argue that reducing the incision size is altogether unnecessary.

The advantages of mini-incision cataract surgery and MICS compared with standard phacoemulsification are well documented [1, 3, 4]; however, many surgeons are still apprehensive to convert their surgical technique for fear of increased complications, including endothelial cell loss [3, 5], intraocular pressure [6], and endophthalmitis [7]. The density of the nucleus affects endothelial cell loss because of the number of small, hard fragments in the anterior chamber [2]; however, when MICS is performed correctly, risk of these complications is minimized. Mencucci et al. [3] performed biaxial MICS with a stop-and-chop phacoemulsification technique and compared endothelial cell loss with that during standard cataract surgery. The investigators found that endothelial cell loss and endothelial morphology was not significantly different between the two groups (difference between the standard group and the MICS group: baseline, 25 cells/mm2; 1 month, 19 cells/mm2; 3 months, 19 cells/mm2).

Any time a surgeon changes the surgical technique, there is the risk of increased complications. This is no different when upgrading from standard phacoemulsification to biaxial or coaxial MICS technique; however, learning to (1) avoid complications and (2) manage them if and when they occur will help the surgeon to overcome the learning curve quickly. Bausch & Lomb developed its so-called MICS Platform to address the issue of the learning curve and make the MICS conversion easier and minimize complications.

First, it helps to understand how MICS works. In biaxial MICS, irrigation and aspiration are separate, allowing the surgeon to create and use smaller incisions during phacoemulsification. Using a sub-1.5-mm incision, biaxial MICS employs a sleeveless phaco tip and a separate irrigating chopper (Fig. 9.3.23). In most instances, one incision is enlarged to at least 1.8 mm to allowing insertion of a foldable IOL (Fig. 9.3.24). However, the use of smaller incisions during the phacoemulsification period means decreasing the outflow and vacuum and increasing the inflow, thus creating a stable anterior chamber. Biaxial MICS also gives the surgeon the ability to control power modulation with

Fig. 9.3.23 Biaxial phacoemulsification: ergonomic balanced light-weight handpiece employing six crystals for increased stroke length with tighter curve for more precise and accurate delivery of US power on demand (optimised 28.5 Hz cavitation)

Fig. 9.3.24 Hydrophilic acrylic foldable one-piece aspheric IOL (MI60, B and L) with 360° sharp edge design for MICS (overview, scanning electron microscopy)

fixed or linear control of onand off-times. One advantage of controlling the power modulation is a reduced risk of wound burn [8]. Coaxial small-incision surgery is also a newer phacoemulsification technique that is gaining popularity. In coaxial, a sleeved phaco tip is used, and the incision size is often enlarged from 1.5 to 1.8-mm (as in my technique). For example, the Stellaris system (Bausch & Lomb) features a 1.8-mm sleeved phaco tip for coaxial MICS in addition to its biaxial MICS phaco tip. The 6-crystal handpiece operates at a lower frequency of 28.5 kHz, using a longer stroke length to optimize cutting and minimize the thermal loading. When using the vacuum mode, additional chamber stability is provided by the StableChamber Tubing System (B&L). The tubing system incorporates restricted tubing and a mesh to capture lens material over 5 mm to protect against post occlusion surge.

Second, the surgeon should know what types of complications are the most common during MICS or mini-incision cataract surgery. During biaxial MICS, complications include occlusion of the phaco tip, which most likely will occur if a high viscosity ophthalmic viscosurgical device (OVD) is used; folds in the cornea, occurring when a small incision is manipulated and the wound stretches; and anterior chamber instability, sometimes caused by a larger incision that creates turbulence in the anterior chamber. Additionally, the surgeon must keep in mind that the use of a small irrigating chopper will limit the amount of irrigation in the eye, which has the tendency to result in an unstable anterior chamber if high vacuum is used [9].

Although some surgeons worry that endothelial cell loss is associated with the use of MICS, Mathys et al. [2] concluded that endothelial cell loss was only weakly associated with the average of phaco power used in foot position three. Although phaco time was slightly longer when using biaxial MICS, endothelial cell loss and proportional loss of cells were not affected by the duration of the procedure. Perhaps the use of OVDs or disorders such as subclinical endothelial or systemic diseases also affect endothelial cell loss. Using power modulation as well as pulse/hyperpulse and burst/hyperburst, such as the custom control software II (CCS II, B and L), should not only reduce the loss of endothelial cells but also provide quicker visual recovery for the patient [10].

Several clinical trials found a greater endothelial cell loss with greater phacoemulsification time and power used [11–14]. Other studies found either no correlation or only a weak association between endothelial cell loss and total phacoemulsification energy and length of procedure [15, 16]. Additional risk factors for an increase in endothelial cell loss include operating on harder cataracts, the size of the cataractous nucleus, infusion volume, and total phaco energy [15, 17]. Mathys et al. [2] found that the nuclear color strongly correlated to the loss of endothelial cells. Furthermore, power modulation during biaxial MICS showed less correlation to central endothelial cell loss, phacoemulsification time, and energy used during surgery.

Recently, my colleagues and I studied the use of biaxial MICS vs. coaxial small-incision in complicated cataract cases, such as exfoliation syndrome, uveitis, anterior or posterior synchia, phacodonesis, or previous intraocular surgery [18]. Of the 94 eyes (94 patients), half underwent biaxial MICS via a 1.5-mm incision and

the other half underwent coaxial small-incision phaco with pulsed ultrasound energy and variable duty cycles. The endothelial cell loss in the biaxial vs. coaxial group was similar, 8 weeks after surgery (343 cells/mm2 vs. 222 cells/mm2). Complications included early postoperative corneal edema surrounding the tunnel, a fibrin reaction in the anterior chamber, and pupillary distortion; however, the most common complications after cataract surgery often include transient corneal edema, wound leakage, elevated intraocular pressure, and fibrin reaction [19–25], and, therefore, our rate of complications was not uncommon. Additionally, we did not have any incidence of elevated intraocular pressure or wound leakage. When biaxial MICS was used, effective phaco time was statistically significantly lower than when coaxial small-incision phaco was performed (median, 1.34 vs. 5.4 s, respectively). Mean phaco power was also lower (3.3 vs. 12.9%, respectively).

Many other surgeons have had success with biaxial MICS as well. Dada et al. [26] performed biaxial MICS in a vitrectomized eye. In combination with silicone oil removal, Data and colleagues concluded that biaxial MICS was a safe alternative to standard phacoemulsification in vitrectomized eyes. Kurz et al. [27] found that patients who underwent biaxial MICS experienced an earlier visual rehabilitation time than standard phacoemulsification. Furthermore, according to Alió et al. [28] biaxial MICS in healthy eyes had a significantly lower mean phaoemulsification time, mean total phacoemulsification percent, mean efficient phacoemulsification time, and surgically induced astigmatism compared with conventional phacoemulsification.

As of recently, many studies have compared the advantages and disadvantages of MICS with standard cataract surgery techniques. Other studies have compared biaxial and coaxial MICS [29–31]; both techniques have been found to be safe and effective alternatives for phacoemulsification. Only time will tell which method will be the most advantageous. In the time being, I suggest researching several MICS techniques and crafting your own.

I am well versed in both coaxial and biaxial MICS. For biaxial MICS, I create a 1.2-mm corneal incision at the 11-o’clock position, parallel to the limbus (in the plane of the cornea). I choose to use the front of a trapezoidal microkeratome. I begin the second incision at the 2-o’clock position (Fig. 9.3.25) and insert the irrigating sleeve through this 1-mm incision. After filling the anterior chamber with Healon (Advanced Medical

Fig. 9.3.25 Trapezoidal two-step self-sealing tunnel incision to maintain chamber stability allows more lateral maneuverability and limit collateral fluid loss

Optics, Inc., Santa Ana, California), I create a continuous curvilinear capsulorhexis with a 24-gauge bent needle. Alternatively, you can use a capsulorhexis forceps designed for MICS. Then, I perform hydrodissection and hydrodelineation. The phaco tip is inserted through the 11-o’clock incision, using my right hand, and the 19-gauge irrigating chopper is inserted through the 2-o’clock incision with my left hand. The irrigating handpiece should go in first to expand the anterior chamber before the phaco tip. If you put the phaco tip in first, you may shallow the anterior chamber and not be able to get the irrigating handpiece in.

Rose [32] suggested that biaxial MICS is the appropriate option for patients with small pupils, endothelial disease, pseudoexfoliation, traumatic cataracts, zonular loss, and high myopia. Rose’s study also suggested, much like Dada et al. [26], that biaxial MICS is safe to use in vitrectomized eyes.

My technique is different for coaxial small-incision surgery. I use a metal microkeratome and make a 2.75mm clear corneal tunnel incision, in two steps, at the 12-o’clock or temporal position. The second step is to use another steel microkeratome to create two 1-mm incisions at the 10and 2-o’clock positions. I again fill the anterior chamber with Healon and perform the capsulorhexis, hydrodissection, and hydrodelineation just as I would for biaxial MICS. I use a 19-gauge, sleeved phaco tip, and two irrigating choppers are inserted into the sideport incisions. A manual chopper is inserted at the 2-o’clock position.

Choosing to learn a MICS technique is, of course, a surgeon’s individual choice; however, accepting the challenge to convert comes with many rewards, including less wound-related complications and quicker visual recovery. Additionally, handling difficult situations and complicated cases is sometimes easier with MICS than with standard phacoemulsification. For these reasons, I suggest investing time and energy in developing a MICS technique. Once the short learning curve is overcome, MICS enhances the surgeon’s ability to offer patients the best surgical option, care, and outcomes possible.

Take Home Pearls

ßUsing power modulation as well as pulse/hyperpulse and burst/hyperburst should not only

reduce the loss of endothelial cells but also provide quicker visual recovery for the patient.

ßAdditional risk factors for an increase in endothelial cell loss include operating on harder

cataracts, the size of the cataractous nucleus, infusion volume, and total phaco energy.

ßBiaxial MICS has a shorter effective phaco time and a lower mean phaco power as com-

pared with coaxial small-incision cataract surgery. Biaxial MICS also provides patients with an earlier visual rehabilitation time.

ßMICS is a safe alternative to standard cataract surgery, with a low rate of complications.

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