Ординатура / Офтальмология / Английские материалы / The Art and the Science of Cataract Surgery_Boyd, Barraquer_2000

Once mastered, this technique is highly reproducible, it takes no longer than any other chop technique, and reduces the amount of ultrasound energy introduced into the eye. It may be a very good alternative procedure for experienced phaco surgeons.

Potential Complications

To critics, this technique appears dangerous. The belief is that the capsular bag can be dislocated. However, Dodick has not found this to be a problem if the recesses of the capsular bag are identified by vacuuming of the anterior cortical material and the hooks are carefully placed in the capsular bag and not in the sulcus. Critics may point out that the tip is back toward the posterior capsule, and the two hooks brought across the nucleus might rip the posterior capsule. This, according to Dodick, does not happen.

On the contrary, he thinks that this can actually be a safer procedure, especially in eyes with weak zonules and pseudoexfoliation. Rather than sculpting and applying pressure toward the zonules, the vector forces from the special hooks pull toward the center, reducing stress on the zonules.

For more dense cataracts (e.g. 3+), he does use low ultrasound, perhaps 15%, maximum 30%, and again high vacuum, 300 to 400 mmHg, and a high flow rate. To minimize the effect of surge, he uses the MAXVAC high vacuum tubing and the aspiration bypass ABS tip.

Contributions of this Technique

Dodick's procedure shows that using mechanical energy to break up the lens in place of ultrasound is helpful in reducing the

T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y

amount of energy necessary to evacuate the lens. The technique Dodick describes is one method of nuclear disassembly. These methods in general dramatically reduce the amount of energy to break up the nucleus, leading to clearer corneas and quicker rehabilitation of the patient after surgery.

THE CHOO-CHOO CHOP AND FLIP PHACOEMULSIFICATION TECHNIQUE

Eye Institute in Eugene, Oregon and Clinical Professor at the Oregon Health Science University in Portland, is a chopping technique that uses power modulations and high vacuum along with specific maneuvers to minimize the amount of ultrasound energy in the eye and maximize safety and control. It is effective in all types of cataracts and allows hardened nuclei to be removed safely in the presence of a compromised endothelium.

This procedure facilitates the achievement of two goals: minimally invasive cataract surgery and maximally rapid visual rehabilitation. It is designed to take maximum advantage of various new technologies available, mainly the Alcon 20,000 Legacy, the AMO Sovereign (Allergan) and the Storz Millennium phacoemulsification systems (Fig. 85). These technologies include high vacuum cassettes and tubing, multiple programmable features on all systems, as well as the Mackool Micro Tip (Fig. 84) with the Legacy and burst mode and occlusion mode capabilities with the Sovereign (Figs. 86, 87). The result is enhanced efficiency, control, and safety. The procedure is done as shown and described in Figs. 122, 123, 124, 125, and 126.

Origin of the Name “Choo-Choo”

Fine uses high vacuum and short bursts, or pulses, of phaco ultrasonic power. The name “choo-choo” arises from the resulting sound of the pulse mode (Fig. 125). The nucleus is continually rotated so that pieshaped segments can be scored and chopped, and then removed by high vacuum assisted by short bursts or pulses of phaco. (Editor’s Note: scoring the nucleus in this instance means using the wedge-shaped edge of the chopper instrument to groove and then cut the nucleus in half against the countering resistance of the phaco tip which has been securely engulfed in the opposite side of the nucleus.)

The short bursts or pulses of ultrasound energy continuously reshape the pie-shaped segments which are kept at the tip, allowing for occlusion and extraction by the vacuum. The size of the pie-shaped segments is customized to the density of the nucleus with smaller segments for denser nuclei. Phaco in burst mode (Fig. 125) or at this low pulse rate (Fig. 86) sounds like “choo-choo-choo- choo”; this is the reason behind the name of this technique. (Editor’s Note: for a precise description and illustration of the pulse and burst modes, and their clinical applications, see pages 151-156, and Figs. 86, 87).

The term “flip” refers to management of the epinucleus (Fig. 126). Fine considers it important not to remove the epinucleus too

early, to avoid leaving a large amount of residual cortex after evacuation of the epinucleus. The epinuclear rim of the fourth quadrant is utilized as a handle to flip the remaining epinucleus.

Comparison With Other Techniques

The choo-choo chop and flip technique utilizes the same hydro forces to disassemble of the nucleus as in cracking techniques, but substitutes mechanical forces (chopping) for

T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y

ultrasound energy (grooving) to further disassemble the nucleus.

High vacuum is utilized to remove nuclear material rather than utilizing ultrasound energy to convert the nucleus to an emulsate that is evacuated by aspiration.

Fine's Parameters

The parameters used by Fine for this technique and applied to the three main phacoemulsification equipments are the following:

THE TRANSITION TO CHOPPING TECHNIQUES

In the transition to chopping, Fine recommends the following steps:

Impale the nucleus on the phaco tip superiorly. If you have not lollipoped the probe tip deep enough (Fig. 88), return to position 2 and then go back into position 3. (Editor’s Note: lollipoping refers to securely engulfing the tip of the phaco into the nucleus, like a lollipop or candy sucker on a stick. The phaco tip is analogous to the stick and the nucleus is the round candy portion.) A burst takes place each time you enter position 3.

When you have lollipoped deeply enough (Fig. 88), score the nucleus. (Editor’s Note: scoring the nucleus means using the wedge-shaped edge of the chopper instrument to groove the nucleus deeply, against the countering resistance from the lollipoped phaco on the opposite side of the nucleus.) Place the chop instrument in the golden ring (Fig. 75), go from foot position 2 into foot position 3 and floor it (Editor’s Note: pushing the pedal fully all the way to the bottom setting, as when applying full gas pedal pressure in a car). You can chop the nucleus without having to worry about what your foot is doing because your foot is on the floor — the vacuum will hold the nucleus as you manipulate the chop instrument.

Then break the nucleus in half by separating the two instruments while depressing the chopper and slightly elevating the phaco needle. You will not have to worry about what your foot is doing because you are already in control of the nucleus — you will not have to manipulate your foot at all. This technique will allow you a much easier transi-

tion with fewer factors to worry about.

For mobilizing the nuclear tissue, Fine likes a burst width of 80 milliseconds in surgeon control (Fig. 87). Once again, you can customize your options to control what happens at the tip. If things are moving along rapidly, you can depress the foot pedal to foot position 3 and decrease the interval between bursts. Or if you feel like things are a little precarious or there is a very hard piece of nucleus and you want to avoid chattering, you can back off a little bit. (Editor’s Note: chattering is when the nucleus bounces against the phaco tip at a high rate of speed without being emulsified as desired, like when ones teeth chatter when cold - Fig. 89)

The material will be held very firmly at the tip with no chatter, and will not emerge into the anterior chamber. This affords a much greater level of safety when dealing with a hard cataract in the presence of endothelial disease.

Once you have taken care of the endonucleus, you can employ the Bimodal feature using the pedal to vary your aspiration flow rate in foot position 2. This helps you to mobilize and bring the epinuclear roof out of the capsular fornix and position it in such a way that you can trim it. Fine trims the rim of the epinucleus in three different quadrants and uses the rim in the remaining quadrant to flip the rest of the epinucleus (Fig. 126). He brings the handpiece central and then trims the epinucleus. Once he goes into foot position 3 the tip clears. As the rim of the epinuclear shell is removed, the aspiration flow rate causes the residual cortex to flow over the floor of the epinuclear plate.

Fine does not usually have to remove the cortex as a separate step of phacoemulsification. In 70 percent of these cases, he has no cortex remaining.

These types of maneuvers can be done because there is a stable anterior chamber with a very low tendency for surge.

The new technology in these advanced machines and new software allows the surgeon to put into effect the important advance in performing phacoemulsification, which is fundamentally cutting power. The surgeon really has little worry about cutting power himself because the new software provides him/her so many more options. With these recent advances in phacoemulsification systems, the surgeon has indeed a total control phaco chop. The new type of software described in Chapter 8, Fig. 85, will advance phacoemulsification in regions of the world where there is a preponderance of hard cataract with diseased endothelium.

REMOVAL OF RESIDUAL

CORTEX AND

EPINUCLEUS

The surgeon who is learning this technique usually has more cortex to aspirate and needs to follow a specific technique for removal of the epinucleus. This is discussed in depth and illustrated in Figs. 69, 70 and 71, Chapter 7. If not cautiously done, there is a higher incidence of rupture of the posterior capsule.

The situation differs for the experienced surgeon. Due to the importance attributed to a well-performed hydrodissection and rotation of the nucleus at the end of it, generally the epinucleus and the residual cortex are

aspirated together with the nucleus segments. The aspiration of cortical remains becomes unnecessary because they were partially or totally eliminated during nucleus emulsification. If this does not happen, the tip of the phaco emulsifier aspirates the free epinucleus with the pedal on position 2, with the help of the nucleus manipulator (Figs. 69 and 126).

Once the nucleus has been removed and the surgeon proceeds to irrigate/aspirate whatever cortex remains, he/she may become over-confident thinking that the operation is practically finished. It is, if the cortex and epinucleus are then removed with special care. Always be certain to check the tip of the I/A phaco tip preoperatively to detect any

little barbs or sharp spots that could rupture or tear the posterior capsule. The Chip and Flip technique advocated by Fine may be very useful in this phase (Fig. 126). The entire epinuclear rim and floor can be evacuated safely and completely.

If some cortical material remains, particularly in the hard-to-reach superior capsular bag underneath the anterior capsule leaves, the surgeon proceeds to remove this residual cortex as shown in Figs. 127 and 128. It is very important not to be aggressive. Do not attempt to clear the very last bit of cortex remaining because this could lead to accidental rupture of the posterior capsule.

INTRAOCULAR LENS IMPLANTATION

The Increased Interest in Foldable IOL's

Present trends point to an increasing use of foldable IOL's for the following reasons:

1) Small incision cataract surgery continues to be on the rise. Patients who are in the financial,social,businessandprofessionallevels to afford phacoemulsification look forward to a very prompt visual rehabilitation. This can be made possible only by a successful phaco with a small, valvulated, self-sealing 3 mm average incision which requires a first class foldable IOL (Figs. 90, 91).

Surgeons, therefore, no longer accept the previous methods of performing a cataract extractionthroughasmallincisionfollowedby an enlargement of the wound in order to insert a6.0mmopticPMMAlens. Asaconsequence, industry rose to this challenge and has developed high quality foldable IOL's .

2) Through the significant clinical and laboratory research made by R. Lindstrom, I.H. Fine, Ernest and Neuhann, Langernman and other prestigious colleagues, refractive cataract surgery was developed as a standard procedure by: a) placing the corneal cataract incision in the right place. b) developing the right architectural design of a small self-seal- ing,valvulated,cornealtunnelincisionthatcan result in 1.00 D or less of postoperative astigmatism (Figs. 92, 93). This has stimulated the useoffoldablemonofocalandmultifocalIOL's.

3) Foldable IOL technology has significantly improved associated with the use of non-toxic, highly biocompatible chemicals and polymers of which the foldable IOL`s are made. This is particularly important with the development of second generation silicone lenseswhichhavebeenproventobenon-toxic, non-inflammatory, non-sensitizing, inert and available at lower costs.

TheMostFrequentlyUsedIOL's

Even though there is a distinct trent towards foldable lenses, PMMA IOL's continue to be the most frequently implanted intraocular lenses throughout the world, (except in the U.S). PMMA IOL’s are used more commonly even in Europe, although to an ever-decreas- ing extent, as has been pointed out by Tobias Neuhann, M.D., of Germany, in a classic study he made of new foldable IOL's (see bibliography).

The still preponderant use of PMMA lenses is related to the unquestionable reality that, for a variety of reasons, extracapsular surgery is still the cataract operation mostly used throughout the globe. More than 60% of verygoodophthalmicsurgeonsperformECCE in the majority of patients even though they may recognize that phacoemulsification is a better operation especially for of very prompt visual rehabilitation.

Special Indications for PMMA Lenses

Richard Lindstrom, M.D. uses foldable lens implants in most cataract operations.