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Single Instrument Phacoemulsification through a Clear Corneal Microincision

Robert M Kershner

Introduction

An increasing number of surgeons have adopted phacoemulsification as the preferred method for cataract removal, since its introduction as a method of cataract removal over one-quarter of a century ago, The advantages of removing a cataract through a small incision have been recognized by surgeons the world over. Phacoemulsification has made it possible to abandon suture closure, utilize smaller incisions, replace injection anesthesia with topical anesthesia, and improve our ability to correct refractive error with cataract surgery.1

Today’s new techniques of topical anesthesia, clear corneal cataract surgery, and injection of elastic intraocular lenses through small incisions have placed new constraints on the ability of the surgeon to perform phacoemulsification. Introducing the phacoemulsification tip through a small clear corneal refractive microincision limits access to the cataract and can restrict the surgeon’s ability to manipulate the lens within the capsular bag. As a result of the challenge and demands of smaller incision cataract surgery, surgeons have adopted several new approaches to the strategy for phacoemulsification.

All methods of cataract removal have essentially one goal in common—to take a large anatomic structure (the lens) and dismantle it into smaller pieces for ease of removal through an incision smaller than the overall size of the lens. Whether one adopts a divide and conquer technique, a quadrantic phacoemulsification method, a chip and flip, or a stop and chop method, the goal remains the same. One can either mechanically divide the cataract into segments and remove the individual segments, or chip away at the larger structure and remove it piece by piece.

Many surgeons use two incisions through the cornea, and two instruments for phaco: one for the phaco tip and one for a sideport lens manipulating instrument. The author does not believe that a second-handed instrument is necessary for effective and efficient phacoemulsification of the cataract. There are distinct advantages of maintaining the phaco incision as one incision. Placing an additional incision in the eye is not only unnecessary, but it increases the likelihood of incisional leaks, an additional portal for infection, synechiae and encourages excessive instrumentation of the eye. We learned to drink a glass of milk as children by holding onto the glass with two hands. As adults, we can learn to hold a glass with one hand, freeing up the other hand for other needs. So, it is with phacoemulsification.

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Single Incision Phacoemulsification: The Four-step Keyhole

Technique

Early in its development, phacoemulsification was performed entirely through a single incision. This single incision or single instrument phacoemulsification technique has previously been called a “one-handed” phaco technique. The name is a misnomer, however, as two hands are required to successfully perform phaco. They just do not each require their own incision! The maneuvers of lens rotation and segmental removal of the cataract can be performed with a single hand on the instrument, thus, freeing the left hand for manipulating the eye, stabilization of the globe, retrieval of instruments, or to hold the phacoemulsification handle and tubing.

It is important that the surgeon adopt an efficient method of phacoemulsification through today’s small corneal microincisions. The single instrument phaco technique is elegant, more efficient, easier to learn, and less traumatic to the eye. The time is right, as we enter the next millennium, to take a new look at an old technique—the single incision or single instrument phacoemulsification method that the author calls the keyhole technique.6

Incision Construction

The clear corneal microincision has placed new demands on the surgeon for evacuating the cataract through a single small corneal incision. These incisions can be very unforgiving—they must not be distorted, torn or heated during the procedure without creating profound refractive effects for the eye.

Incision construction is critical to a successful phacoemulsification procedure. The incision needs to be accurately sized for the size of the phacoemulsification tip to be used. Today’s microincision corneal procedures utilize an incision of 2.5 mm or smaller that must accommodate a micro phaco tip. The clear corneal refractive microincision technique has been described elsewhere.1–3 Following fabrication of the clear corneal incision with a diamond keratome, the anterior chamber is entered, and a viscoelastic placed to deepen the chamber. Capsulorhexis is performed using the technique of onestep capsulorhexis with a cystotome/forceps which the author developed in 1984.4,5

In early phacoemulsification methods, it was important to maintain the position of the cataractous lens within the capsular bag to stabilize it. Following the introduction of capsulorhexis, it was found that the limited access into the capsular bag created difficulties for the surgeon in rotating the lens for emulsification and removal. To facilitate these maneuvers, hydrodissection must be performed to cleave the strong cortical attachments between the lens capsule and the cortex of the cataract. By slipping a curved 27-gauge cannula through the incision and positioning it beneath the subincisional anterior lens capsule, a fluid wave can be created across the posterior lens. This maneuver prematurely loosens the cortex beneath the incision making it easier to remove with irrigation and aspiration later in the procedure.

Phacoemulsification Parameters

It is preferable to use a phacoemulsification machine whose individual parameters are controllable by the surgeon. When utilizing a peristaltic pump, the factors of flow rate, rise time, vacuum and phacoemulsification power can be set to the individual needs of the surgeon. By setting the flow rate, the surgeon can control how rapidly the fluid moves into the eye and out of the aspiration port. This is important in cooling the phacoemulsification tip during brief bursts of phaco power. The faster the flow rate, the quicker the rise time, and the more fluid which is utilized during aspiration. The vacuum level can also be set by the surgeon. Under normal conditions, the vacuum level is zero until the aspiration port of the phacoemulsification tip is occluded, when it will reach the maximum preset. As soon as the occlusion is broken, the vacuum will return to zero. Phacoemulsification power should be set to a reasonable level which allows the surgeon adequate control with the phaco pedal. The author will rarely use phaco powers above 30 to 40 percent maximum. For most cataracts, the author uses a vacuum level of between 150 and 200 mm Hg and a flow rate of approximately 20 to 50 rpm of the peristaltic pump (4–6 cc/minute). The higher the height of the infusion bottle, the greater the pressure head of fluid within the eye. With single incision phacoemulsification, a higher head of pressure is required. This maintains the chamber, and allows the delicate maneuvers with the phaco tip without danger of collapsing the capsular bag or injuring the corneal endothelium.

Phacoemulsification tips are available in zero degree, 15 degree, 30 degree, and 45 degree angulations. For most purposes, a 30 degree angulated tip is most effective for soft to medium cataracts. Hard cataracts should be removed using a 45 degree tip which has a sharper cutting edge but less occludability.

Step 1: Central Sculpting

When performing central sculpting, occlusion of the phacoemulsification tip rarely occurs. Therefore vacuum levels can be quite low (less than 20 mm Hg). In fact, vacuum levels of zero for central sculpting work quite well. Low flow rates are required during the central sculpting maneuver. The goal of central sculpting is to remove the densest, hardest part of the nucleus at the beginning of the procedure when it is easiest to do so. The lens is kept entirely within the capsular bag. Using the phacoemulsification tip, gentle sculpting of the central nucleus is carried out (Fig. 22.1). Many surgeons wonder how far and how deep they should sculpt? Fortunately, there is a way to measure within the eye when performing phacoemulsification. The phaco tip is approximately 1 mm in width, and therefore three phaco tip width is approximately 3 mm deep. The average cataractous lens is at least 4.5 mm in anterior/posterior thickness, therefore one would have to place the phaco tip at least 3 to 4 tip width deep until the posterior capsule is encountered. With gentle aspiration and emulsification, the central nucleus can be safely and completely removed without damaging the posterior capsule. In soft lenses, the author suggests keeping the emulsification furrows narrow and shallow to leave enough cortical rim to be removed in the second and third steps. With hard, more mature cataracts, wide sculpting of the central dense nucleus and sculpting deep up to the level of

Step 2: Creating an Inferior Notch: The Keyhole Method

Once central sculpting is completed, the surgeon is left with a cortical bowl. To remove the cortical bowl, an inferior notch must be aspirated to release the tension on the cortical ring of the cataract (Fig. 22.2). Low-power phacoemulsification and a higher vacuum is required to adequately aspirate and remove two clock hours of cortical rim. By gently placing the phacoemulsification tip at the edge of the lens capsule, the cortex can be aspirated into the tip and the vacuum level will rise. A small section of the rim can be aspirated and pulled into the center of the pupil. Here it is in the deepest portion of the chamber and furthest from the lens capsule, capsular rim, iris and endothelium. This is the triangle of safety which is an imaginary triangle bordered by the corneal incision at the apex and the east and west edges of the pupil. Only within this region should emulsification be performed (Fig. 22.3).

Step 3: Removal of the Cortical Rim

Using the phacoemulsification tip as a fulcrum, the remaining cortical rim can be gently rotated counterclockwise. The rotational maneuver is

FIGURE 22.3 The triangle of safety— that region bounded by the incision and the east and west margins of the pupil where the anterior chamber is deepest and the furthest distance from the phacoemulsification tip to the corneal endothelium and the posterior capsule. The safest zone in which to perform phacoemulsification

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performed as follows: the tip is gently embedded into the cortical rim at a convenient location (usually 3 O’clock), the tip is brought to the center of the lens within the triangle of safety along with the rim of cortical cataract and gently emulsified (Fig. 22.4). Consecutive low levels of emulsification power are applied until each individual quadrant is removed.

Step 4: Removal of the Nuclear Plate

Following complete removal of the cortical rim, a small flat section of posterior nucleus remains. The phacoemulsification tip is turned over (bevel down) and placed flat against this plate. Using very low levels of aspiration, the remaining nuclear plate is elevated off the posterior capsule and removed (Fig. 22.5). Low power levels are used at this the final stage of cataract removal. To enhance followability, the surgeon can select pulsed phaco mode. This prevents excessive pushing away of the final piece when emulsification is engaged. Avoid the tendency to chase the final piece around the chamber—

FIGURE 22.4 Step 3—Removal of the cortical rim

patience is rewarded if the surgeon waits for the piece to come to the tip.

Before removing the phacoemulsification tip, check on either side of the incision for any loose remaining pieces of nucleus, which should be removed prior to completing the phacoemulsification procedure.

FIGURE 22.5 Step 4—Removal of the nuclear plate

Conclusion

The single instrument phacoemulsification procedure is quick, requires only one incision, one instrument and is less traumatic to the eye. The benefits of this technique are less induced astigmatism, more rapid visual recovery, better uncorrected visual acuity and a happier patient.1 Any difficulties encountered when using a single instrument technique are quickly overcome when the surgeon performs all of the maneuvers of central sculpting, aspiration of cortical rim, nuclear rotation and removal of the nuclear plate using just one instrument—the phacoemulsification tip alone.

The single incision or single instrument approach to phacoemulsification paves the way to a fully integrated microincision refractive cataract procedure. With less portals into the eye, the procedure is amenable to topical anesthesia. Suturing is no longer required. Bandaging is unnecessary. The single microincision allows injection of onepiece elastic intraocular lenses without enlarging the incision. The patient’s refractive status can therefore be taken into account when correcting both spherical and astigmatic error simultaneously with one procedure. By using a single incision, implantation of a toric or multif ocal intraocular lens is facilitated. This translates into immediate visual recovery for the patient, without glasses.

The ultimate goal of outpatient cataract surgery is less intervention with better visual results and more rapid visual rehabilitation. As our techniques to remove a cataract and implant an intraocular lens evolve toward smaller and smaller incisions, the single instrument method of phacoemulsification will become appealing to more and more surgeons.

References

1.Kershner RM: Clear corneal cataract surgery and the correction of myopia, hyperopia and astigmatism. Ophthalmology 104(3):381–89, 1997.

2.Kershner RM (Ed.): Refractive Keratotomy for Cataract Surgery and the Correction of Astigmatism Thorofare: Slack, 1994.

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3.Kershner RM: Keratolencticuloplasty—arcuate keratotomy for cataract surgery and astigmatism.

J Cataract Refract Surg 21:274–77, 1995.

4.Kershner RM: One-step forceps for capsulorhexis. J Cataract Refract Surg 16:762–65, 1990.

5.Kershner RM: Embryology, anatomy and needle capsulotomy. In Koch PS, Davison JA (Eds):

Textbook of Advanced Phacoemulsification Techniques Thorofare: Slack, 35–48, 1991.

6.Kershner RM: Sutureless one-handed intercapsular phacoemulsification—the keyhole technique.

J Cataract Refract Surg 17(suppl):719–25, 1991.