37

Erbium-YAG Laser Cataract Surgery

Demetrio Pita-Salorio

Guillermo L Simon Castellvi

Jesús Costa-Vila, Marc Canals-lmhor

JR Fontenla, J Laiseca

Introduction

Most North American and European surgeons agree today that ultrasonic cataract surgery, when possible is the safest and the one with the shortest visual recovery.

Very soon ocular surgeons worldwide will be able to use the upmost of laser technology for cataract surgery. In the authors’ hands the first European erbium-yttrium aluminum garnet (Er-YAG) laser prototypes have shown to be effective, and, as they have been developing the first European prototypes, they have found that Er-YAG laser surgical approach to cataracts slightly differs from that of classical ultrasonic phacos.

Brief History of European Laser Cataract Surgery

The idea of substituting ultrasounds for another kind of energy is not new. Many have been the lasers under research for cataract surgery. Some are still under development, others—like ultraviolet lasers—were abandoned years ago due to their mutagenic and carcinogenic side effects. Alternatives to ultrasonic emulsifiers for cataract surgery include various instruments and lasers, with different wavelengths of laser energy. The wavelengths currently under investigation for opacified crystalline lens removal include the following (Table 37.1).

To date, the pursuit of the appropriate wavelength has centered around the neodymium: yttrium aluminum garnet (Nd: YAG) and the Erbium: YAG.

TABLE 37.1 Wavelengths under investigation for opacified crystalline lens removal

•1,064 nm neodymium: yttrium aluminum garnet (Nd: YAG)

•1,047 nm neodymium: yttrium lithium fluoride (ND: YLF)

•1,053 nm with picosecond pulses

•2,940 nm (Er: YAG)

•193 nm, 248 nm, 308 nm, and 351 nm ultraviolet laser wavelengths (excimer lasers)

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FIGURE 37.1 Aesculap Laser. Picture shows the first prototype of Erbium: YAG laser for cataract surgery we developed in the early nineties. It was made by the German AesculapMeditec™ in Heroldsberg, according to our first specifications. This first prototype did not—and still does not in 1998—incorporate an irrigating/aspirating system in the same instrument. An external I/A system has to be purchased separately to perform cataract surgery

The development of the European Er: YAG phaco laser started in 1992, when Professor Pita-Salorio suggested the use of this kind of laser for cataract surgery to AesculapMeditec™ (Fig. 37.1). Aesculap-Meditec™ owned an Er: YAG used for glaucoma surgery (for ab externo fistulizing surgery—laser sclerostomy). Months later, the first prototype of laser built to our specifications—with the obvious first technical limitations—was given to us, and we started the development of laser that was due to be a new tool for cataract surgery.

We performed some in vitro studies, with human cataractous lenses (eye bank lenses), to study the tissular effects of this kind of laser on human crystalline lens.

The first prototype did not have I/A system, only a fiberoptic and different tips for laser

FIGURES 37.2A AND B Pictures show the first generation of tips at high magnification—some were straight, others bent, with different diameters. The fiberoptic core had also different diameters, and slightly protruded from the metal sleeve, easing the contact with the lens material (arrow)

application on the eye (Figs 37.2A and B). This laser forced two-handed surgery, with the laser tip in one hand and the I/A system in the other (through a paracentesis).

After checking the usefulness of the laser to ablate cataracts, we started the first in vivo studies with human volunteers. The fiberoptics proved to be extremely fragile, and the tips bulky, uncomfortable to manage and not perfectly designed. Aesculap-Meditec™ protected and improved the fiberoptics and made the second generation of tips (Fig. 37.3) to design (with I/A, through an external I/A system, we used the Storz Premiere™ phaco I/A system).

We soon found new problems—we observed an energy loss throughout the fiber. Day after day, the energy loss increased inside the fiberoptic, until the

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FIGURE 37.3 Picture shows the first and second generation of laser tips for the early Aesculap-Meditec Er: YAG MCL-29 Phacolase. The first generation (top) did not incorporate I/A system in the handpiece, while the second generation (bottom) handpiece incorporated the possibility of using an external I/A system the way we are used to with ultrasonic phacos. Nevertheless, a separated I/A system had to be purchased

fiber became useless. New fibers had to be designed. At this time, we suggested to make a new instrument combining the laser and the I/A system—nobody would buy a laser without an I/A system! But Aesculap-Meditec™ did not manufacture it, and they still have not achieved.

When Aesculap-Meditec™ relocated to the former East Germany in 1996, employees who decided to remain in the West formed Wavelight Laser Technology™. Following the split, Wavelight™ focussed on developing a new laser phaco system with the benefit of incorporating past experience.

Wavelight engineers came up with the Adagio™, that produces pulse energy of 100 mJ and 100 Hz. It incorporates a conventional I/A system in the same instrument. This system provides the possibility to work with smaller tips.

Why Er: YAG? The Reason to Choose the Er: YAG

Unlike other wavelengths, the Er: YAG boasts the highest absorption of energy in water of any laser

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FIGURE 37.5 Mechanism of tissular damage

are higher than 100°C, vaporization of tissue water occurs. The liquid water changes into gas (vapor), with a dramatic volume expansion that leads to tissular damage because of the formation and collapse of vapor cavities—it is what we call vaporization (Fig. 37.5). This laser-induced vaporization is accompanied by the formation of acoustic transients (pressure waves) that also produce mechanical damage to the tissue.

Unwillingly, at the same time, the proteins of the lens coagulate, progressively increasing lens hardness, and making tissular lens photoemulsification more difficult as surgery progresses.

One of the vital points to lessen this problem is to use the laser in a pulsed mode. Every pulsed mode has an effective energy (at the beginning of the pulse) and an uneffective energy at the end of the pulse, i.e. wasted as a thermic increase without tissular damage. The higher the frequency, the more effective will be the laser. But too much frequency leads to an enormous energy amount that dehydrates and cooks lens tissues. Correctly balancing energy and frequency are extremely important.

Tissular Effects

In 1995, to evaluate the tissular effects of the new experimental European erbium: YAG (Er: YAG) phaco laser on the human cataractous crystalline lens, we ruled a first in vitro trial with a limited number of human eye bank crystalline lenses, to determine the mechanism of damage and the utility of the European Er: YAG phaco laser to emulsify cataractous lens cortex and nucleus. We show and discuss the tissular effects of this laser, as observed through electron scanning microscope, at increasing energy levels, both in aerial medium and underwater (like in real surgery).

Twenty human eye bank cataractous crystalline lenses underwent laser effect in two groups (in aerial medium and underwater), at different increasing energy levels. After perpendicular laser irradiation, each lens was preserved in a glutaraldehyde solution and sent to our ocular morphology investigation unit to be processed and examined under electronic scanning microscope.

Laser application time was set in all cases to 3 seconds, frequency was set in all cases to 10 pulses per second (10 Hertz). Laser application was directly perpendicular to the lens, at its center.

Results

We briefly show and discuss the tissular effects of this laser, as observed through electron scanning microscope, at increasing energy levels, both in aerial medium (Figs 37.6A to E) and underwater {(Figs 37.6F and G) in real surgery}.

Group A: Eye Bank Lenses, in Aerial Medium

1.Energy level: 10 mJ (10 Hz, 3 seconds) (Fig. 37.6A)

2.Energy level: 20 mJ (10 Hz, 3 seconds) (Fig. 37.6B)

3.Energy level: 30 mJ (10 Hz, 3 seconds) (Fig. 37.6C)

4.Energy level: 80 mJ (10 Hz, 3 seconds) (Fig. 37.6D)

5.Energy level: 100 mJ (10 Hz, 3 seconds) (Fig. 37.6E)

Group B: Eye Bank Lenses, Underwater (Under BSS, Like in Real

Surgical Conditions)

The scanning electron micrographs show an Er: YAG crater at 20 mJ (3 seconds of irradiation at 10 pulses per second), with the European Er: YAG laser (Fig. 37.6F).

Observe that the borders of the crater show clear exfoliative tissular disruption (similar to Nd: YAG laser effect), while deep smooth crater walls are due to tissular ablation (similar to excimer laser effect).

1. Energy level: 10 mJ {(10 Hz, 3 seconds) (Fig. 37.6A)}

FIGURE 37.6A Lens anterior capsule has been disrupted, and only superficial lens cortex has been damaged. This picture confirms23–25 that, in air, Er: YAG laser has a very short penetrating effect over crystalline lens at this energy level, and may be used for anterior circular continuous capsulotomy

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2. Energy level: 20 mJ {(10 Hz, 3 seconds) (Fig. 37.6B)}

FIGURE 37.6B Anterior capsule and cortex have been damaged. The central round crater shows the point where laser tip contacted the lens. Its walls are razor sharp. Laser tissular damage has spread far (1–2 mm) from the contact point, showing that in aerial conditions laser collateral effects may not be so circumscribed as postulated by other authors. The linear cotton fiber is an undesired artifact from the operating room

3. Energy level: 30 mJ {(10 Hz, 3 seconds) (Fig. 37.6C)}

FIGURE 37.6C Er: YAG laser disruptive effect can be clearly observed—it seems as if a group of small explosions (the different pulses) had occurred inside the lens. The image is similar to that obtained by

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much deeper than the obtained in aerial medium. Mass loss is much higher underwater than in air—the European Er: YAG works much better with a film of water between lens and cataract tip

FIGURE 37.6E Er: YAG laser disruptive effect can be observed in superficial lens layers—observe that the borders of the crater show clear exfoliative tissular disruption. In deep, smooth crater walls are due to tissular ablation. The deepness of the crater increases with energy level. In 3 seconds, at 100 mJ we reach one-third of lens thickness

aerial medium, disruption prevails over ablation. Underwater, in surgical conditions, ablation prevails over disruption.

In vitro Er: YAG ablation does not confirm to a linear model—the European Er: YAG laser “mass loss versus fluence” curve is still to be stated. The penetrating effects over crystalline lens increase with energy levels, either in air or underwater. Under certain conditions (high energy levels, in aerial conditions), the extent of surrounding tissue damaged may not be as

FIGURE 37.6G Note the smooth walls of the crater, showing no tissular disruption, though clear-cut tissular ablation

limited as previously stated. Fortunately, this seems less important under real surgical conditions (underwater).

To obtain the best result with this laser, there must be a small quantity of aqueous humor (or irrigating balanced solution) between the laser tip and lens surface—the laser energy is better absorbed, and destroys lens tissue, because of vaporization and acoustic effects. If laser acts on a dry crystalline lens, there is more thermal damage with coagulation and necrosis of the target (tissular disruption). Er: YAG thermal damage depends on the tissular absorption coefficient, which varies with water contents of the tissue, and the presence or not of a small quantity of water between laser tip and the lens. The lens tissue absorption coefficient of Er: YAG increases from 439+/−151 cm−1 in ambient air to 12.800+/−400 cm−1 in water—for this last value, cavitation phenomena with bubble formation are added to heat production, producing more tissular damage.

Adagio™ by Wavelight™ Laser Technology GmbH

Today, we use the Adagio™, a laser final prototype made in Erlangen-Tennenlohe, in Germany by Wavelight™ Laser technology GmbH (Figs 37.7A to C and Table 37.3). In our clinical research, we use the serial number 1002–1–009. This phaco laser integrates in one instrument an erbium: YAG laser system, a peristaltic vacuum system, and a diathermy unit. A special tip allows circular continuous laser capsulotomy The same instrument, with different tips allows cataract surgery, iridectomy, vitrectomy (?) and antiglaucomatous ab externo laser sclerostomy.

With the Adagio™, pulsed laser energy is used to vaporize and photofragment (emulsify) high water contents lens material out of the eye. With the newly designed probes, irrigation, aspiration and laser are simultaneously transmitted to a precise location in the eye through a single small incision. Adagio™ has an integrated water cooling and does not require any special installation practices.

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micrometer-core zirconium fluoride fiber reveals significant damage at the surface. The utility and resistance of these fibers have improved in the last few years. (Picture taken from “Improved Erbium Laser Parameters” by Klaus Vogler and Max Reindl, in Biophotonics InternationalNovember/December 1996. Page 41)

Cataract Surgical Procedure

The initial approach to cataract surgery is much similar to classical ultrasonic phaco technique. The main difference is that instead of mechanical ultrasonic energy, laser energy is used. Surgery can be performed under local (retro or peribulbar, topical or intraocular) or general anesthesia. Wide

FIGURE 37.10 Wide mydriasis is preferable, though not essential. It allows better surgical view. We have noticed that pupil tends to contract as laser progresses

mydriasis is preferable, though not essential (Fig. 37.10).

We prefer a slightly side-incision (temporal) approach to ease surgical maneuvers with the laser tip. A clear corneal single plane 2.5-mm incision is made, being the gateway for laser phacoemulsification and for foldable IOL implantation. Smaller incisions will soon be able with new phaco laser tips.

After the incision has been completed, viscoelastic (any of the currently used substances) is injected to fill the anterior chamber, and thus protect corneal endothelium from shockwave damage. Performing a clear-cornea paracentesis in the opposite side is preferable for better rotation and positioning of nuclear fragments.

Capsulorhexis may be performed either using a cystitome (30 G bent needle, the classical way), the

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FIGURE 37.11 When capsulorhexis is performed with the special capsulorhexis laser tip, it is less regular than mechanical capsulorhexis with the cystitome or the Utrata forceps

FIGURE 37.12 A special capsulorhexis laser tip has been designed to allow continuous circular laser anterior capsulotomy

Utrata’s forceps, or a specially designed laser capsulorhexis tip (Fig. 37.11). This laser tip allows circular continuous laser capsulotomy (capsulorhexis) even in cataracts without red reflex (Fig. 37.12). One important point to ease surgery is performing a wide capsulorhexis—this will allow luxation of the superior pole of the dissected nucleus and cortex to better and faster fragment it with the Er: YAG laser. The goal is to use the lowest possible energy levels, to make phaco laser a safe technique.

Hydrodissection and hydrodemarcation of the cortex and nucleus follow, with balanced salt solution (BSS) and a 27 gauge anterior chamber cannula. Up to now there are no surgical differences with ultrasonic phacoemulsification technique. Whatever technique you are using, good nuclear rotation is essential.

Cortex remnants are aspirated using a standard I/A probe, followed in the end with the insertion of a posterior IOL, preferably foldable IOL. We either use silicone lenses, acrylics or hema with polymethyl-methacrylate (PMMA) rigid haptics (Fig. 37.14). The ideal foldable or injectable, and stable IOL has yet to be invented.

Even with a complete rhexis and whatever method is used to remove the nucleus, a break may result. Even so, using Adagio™ phaco laser we find that rhexis breaks enlarge less in proportion to what happens with ultrasonic phaco in similar cases (Fig. 37.15).

Frequency and Energy: Vital Parameters

A no vice will experiment some difficulty in balancing frequency and energy levels. The correct management of both parameters is essential to avoid “cooking” lens proteins and dehydrating lens material. In summary, we can say that hard nucleus need low frequency and high energy soft cataracts need high frequencies and low energy levels. Personal experience allows better balancing of both parameters.

Both can be controlled on the computer touch panel. If the laser mode (energy and frequency) is set to panel control, the full preset power will be reached as soon as the pedal reaches the “laser position” (I/A+laser).

Adagio™ laser can also be set to linear control, which gives progressively more laser energy and/ or frequency as the pedal is progressively depressed.

The foot pedal has also reflux control that reverses flow, so that fluid (capsule or iris) will flow out of the aspiration port.

The AdagioR Er: YAG laser seems well suited to cut the high water-content structures of the eye, specially the cataractous soft crystalline lens. Nevertheless, far more research is necessary until this laser might be widely used for intraocular cataract surgery.

Postoperative Evolution

Typical postoperative aspect and evolution does not differ from that of an ultrasonic phacoemulsification for an uncomplicated surgery. Mild corneal edema at the incision is seen if manipulation is excessive, the energy dissipation in the incision area being negligible. Minimal postoperative inflammation and endothelial cell loss are the rule for uncomplicated surgery The endothelial cell loss seems very similar to that of our first ultrasonic phacos, and should improve as we get experienced with this new tool (Fig. 37.16). Complete results of our studies are still awaited.

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FIGURE 37.16 Postoperative aspect of uncomplicated patients treated with the Erbium: YAG Wavelight Adagio system does not differ at all from that of patients treated with ultrasounds. Nevertheless, we have observed a mild increase of the intraocular pressure the first days after surgery. This IOP increase was common in patients that underwent the first ultrasonic cataract surgeries

FIGURE 37.17 IOP rise

Mild to moderate intraocular pressure rise is common a couple of days after surgery (Fig. 37.17). Postoperative medication may be necessary in patients with advanced glaucomatous optic nerve damage.

Short-term follow-up of our first patients has revealed no adverse effects or extraordinary complications.

In our clinical study with volunteer patients, we also perform corneal topography, before surgery and three months after surgery. Preliminary results seem to show that

there are no special topographic changes that might be attributable to Er: YAG. Corneal topographic changes do not differ from that of ultrasonics.

Anterior Chamber Temperature

Since Er: YAG laser use in human eyes still raises some safety concerns, we are also checking temperature rise in anterior chamber. For an uncomplicated surgery of about 10 to 15 minutes, temperature rise is lower than 10°C, and should suppose no special danger for endothelium, as it reverses after a few minutes. I/A system minimizes temperature rise, as it permanently cleans and refreshes anterior chamber. At the energy levels we use (20–60 mJ), there is actually no need for cold BSS. As we are planning to increase energy levels in a close future in order to be able to deal with harder nuclei, the use of cold BSS will probably become necessary.

Conclusion

The Er: YAG phaco laser works at its best with soft and middle-soft cataracts, yet has some important difficulty with middle hardness and hard nuclei (Table 37.4). Nevertheless we are sure laser will soon be a major force in cataract removal. The incision size is getting smaller and smaller, minimizing postoperative astigmatism. To new small-incision surgeons, it has the advantage of a shorter learning curve. Experienced surgeons will have to slightly modify their phaco technique, and will be satisfied to use a modern new tool that may achieve cataract surgery in a safer and easier way.

Initially dismissed as being unsafe and not effective enough, we believe that through perseveration, Er: YAG phaco laser improvements will develop into a procedure that will gain worldwide acceptance as a safe effective method of removing cataracts (see Chart 37.1). But there is still a long way to go, a lot of work to be done.

TABLE 37.4 Advantages and disadvantages of Er: YAG

Advantages

•Effectively removes cataractous lens cortex and nucleus (in soft and middle hardness nuclei)

•Best absorption under water

•Safe and easy to learn

does not directly damage adjacent tissues

less thermal damage

endothelial cell loss not worse than ultrasound

•Many potential different ophthalmic uses (cataract, glaucoma, retinal and

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vitreous surgery, cosmetic surgery)

Disadvantages

•“Slow”—ablation mass smaller than other techniques (ultrasound, Ho: YAG laser?)

•Not risk free (posterior capsule break, IOP rise)

•“Fragile” and “perishable” fiberoptics

•Still some technical problems to be solved

•Expensive?

•Does not work properly with hard nuclei

Further Reading

1.Agarwal S: Laser can be used to ablate cataracts. Ocular Surgery News (International ed)

8(9):1997.

2.Bath PE: Laserphaco—an introduction and review. Ophthalmic Laser Ther 3(2):75–82, 1988.

3.Bath PE, Kar H, Apple DJ et al: Endocapsular excimer laser phakoablation through a 1-mm incision. Ophthalmic Laser Ther 2(4):245–48, 1987.

4.Bath PE, Mueller G, Apple DJ et al: Excimer laser lens ablation (letter). Arch Ophthalmol 105:1164–65, 1987.

5.Bonnie SR, Puliafito CA: Erbium: YAG and Holmium: YAG laser ablation of the lens. Lasers Surg Med 15:74–82, 1994.

6.Borkman RF: Cataracts and photochemical damage in the lens. Ciba Found Symp 106:88–109, 1984.

7.Brown S: The multipurpose 1053 picosecond laser. Presented at the American Society of Cataract and Refractive Surgery (ASCRS) Annual Meeting, 1990.

8.Cleary SF: Laser pulses and the generation of acoustic transients in biological material. In Wolbarsht ML (Ed): Laser Applications in Medicine and Biology New York: Plenum Press,

3:175–219, 1977.

9.Cleary SF, Hamrick PE: Laser induced transients in the mammalian eye. J Acoustic Soc Am 46:1037–44, 1969.

10.Colvard DM: Erbium: YAG laser removal of cataracts. Presented at the American Society of Cataract and Refractive Surgery (ASCRS) Annual Meeting, 1993.

CHART 37.1 Wavelight Adagio™: Er-YAG laser cataract surgery

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40.Visuri SR, Pristowsky JB, Walsh JT: Er: YAG laser ablation of pairie dog gallbladder epithelium for the prevention of gallstones. Laser Surg Med 4(15):358, 1994.

41.Wang Kang-sun, Li Qi, Lan Zhi-lin: Comparison of Er: YAG and excimer laser corneal ablation in rabbits. Lasers Light Ophthalmol 2:69,1994.

42.Wetzel W, Häring G, Brinkmann R et al: Laser sclerostomy ab externo using the erbium: YAG laser. German J Ophthalmol 2:1–4, 1993.

43.Wetzel W, Scheu M: A new application system for laser sclerostomy ab externo. Laser Light Ophthalmol 5(4):193–98, 1993.

44.Williamson WA, Aretz HT, Weng G: In vitro decalcification of aortic valve leaflets with the Er: YAG laser, Ho: YAG laser, and the cavitron ultrasound surgical aspirator. Laser in Surg and Med 4(13):421, 1993.