Tips & Techniques for Laser Phacoemulsification
Experienced users offer advice on performing laser cataract removal.
By Mark Packer, M.D., I. Howard Fine, M.D., Richard S. Hoffman, M.D.

Laser phacoemulsification is a promising part of cataract surgery evolution. It still has limitations, including difficulty in removing dense nuclei, but our experience shows that laser phacoemulsification is gentle to the eye, producing exceptionally clear corneas and excellent uncorrected visual acuity on postoperative day one.

Laser-based cataract extraction systems currently include:

• the Erbium:YAG Phacolase (Carl Zeiss Meditec)
• the Nd:YAG Photon Laser System (Paradigm Medical)
• the Q-switched Nd:YAG Dodick Laser PhotoLysis System (A.R.C. Laser GmbH).

Only the Dodick system is approved for sale in the United States, but Paradigm's Photon system is working toward FDA approval, and all three systems are in use in other countries around the world.

Here, we'd like to share some of the techniques we've developed using the Erbium:YAG laser, along with the latest information regarding Paradigm Medical's Photon Laser System. In addition, Laurence T. D. Sperber, M.D. discusses four techniques for bimanual laser photolysis using the Dodick system (see page 49).

The Erbium:YAG Phacolase

Zeiss' Phacolase, which employs Erbium:YAG laser technology, delivers its 2940-nm laser energy via a fiber inside the aspiration port, placed flush with the tip. This laser energy is well absorbed by tissues with high water content, and has a penetration depth of less than 1 micron.

Because the absence of thermal energy allows the separation of irrigation from the application of laser energy and aspiration, you can employ either a bimanual technique, which only requires a very small incision, or the more familiar coaxial set up.

Here's a protocol for the phaco portion of surgery that we find to be very effective:

Setup. When you place the irrigation sleeve around the aspiration port, set the laser to variable frequency mode at 10 to 80 Hz, the vacuum at 350 mmHg, and flow rate at 28 cc/min. Maintain bottle height at 49 inches above the adjustment knob on the pole. Use continuous irrigation to ensure a stable chamber when the laser tip is inserted.

Prechop. We use Takayuki Akahoshi's counter prechop technique to disassemble the lens nucleus:

• Insert a horizontal chopper such as the Fine-Nagahara chopper (Rhein Medical) via the side-port. Touch it against the anterior lens surface and gently push it under the distal anterior capsular flap, so that it falls into the golden ring.
• Use the chopper to support the nucleus while you pass the Akahoshi Prechopper (ASICO) through the 2.5-mm corneal incision directly into the core of the nucleus. Hold the chopper in the golden ring in front of the prechopper to keep the nucleus from rotating. Bisect the nucleus by opening the prechopper.
• Rotate the nucleus 90° and bisect the two hemi-nuclei in a similar fashion. In this way you can divide the nucleus into segments that are a suitable size for laser phacoemulsification.

Emulsify and aspirate. Bring each segment of the now disassembled nucleus to the laser tip with the chopper and support it during emulsification and aspiration.

• Hold the nuclear segments against the laser tip as you increase vacuum gradually and apply laser power to emulsify and extract the material. (The Phacolase's bidirectional foot pedal allows separate control of vacuum and laser.)
• Once you've extracted the segments of the first hemi-nucleus, rotate the remaining nuclear material distally. Use the chopper to support the nuclear material during emulsification and extraction.
• Occasionally you can bring a segment of nucleus to the center of the pupil by applying vacuum with the laser tip, but in most cases you'll need the support of the chopper.

One important caveat: Despite the short (1-micron) penetration of the Erbium:YAG laser, it's possible for evaporation bubbles to line up at the tip, which can create cavities up to 3 mm deep. You need to take this possibility into account when working in the endocapsular space.

Because this laser is generally safe for use near the endothelium, it may be prudent to perform laser evaporation of lens material in the iris plane rather than deep in the bag. (It's also good to keep the tip moving when working in the capsule.)

Extract the epinucleus and cortical remnants. Once you've completely extracted the nucleus, the epinuclear shell will remain in the capsular bag.

• Purchase the rim of the epinucleus with the laser tip and pull it centrally using vacuum. (You can place the chop instrument posteriorly against the floor of the epinucleus and rotate it distally to encourage anterior movement.) Generally, you can aspirate one half to one third of the epinucleus into the laser tip from a single purchase point. Use mostly vacuum, and apply laser gently as required.
• Rotate the epinucleus with the chopper and repeat the process.

Following complete extraction of the epinucleus, remove the laser tip and chopper. Use the Venturi effect option on the Geuder Megatron for irrigation/aspiration of cortical remnants, set at 450 mmHg vacuum and 50 cc/min flow rate. Leave the bottle height unchanged.

The Nd:YAG approach

Both the Photon Laser System from Paradigm Medical and the Dodick Laser PhotoLysis System use this technology; it's a very low energy modality. (Kanellopoulos reported a mean intraocular energy use of 5.65 Joules per case, which compares favorably with values previously reported for ultrasound phaco.)

	The ski-shaped tip of Paradigm Medical's Photon Laser System acts as a photon trap.

These two instruments use the laser in very different ways. Paradigm's Photon disrupts tissue by placing it directly in the path of the laser. In contrast, the Dodick system contains the laser energy inside the tip; the photons strike a block of titanium, producing a shockwave which disrupts the tissue. (For more about the Dodick system, see "Tips and Techniques for Dodick Laser PhotoLysis," on the next page.)

The Paradigm Photon system is coupled to the Mentor SIStem peristaltic irrigation/aspiration pump, and it features a probe with a ski-shaped distal tip. The aspiration inlet is placed in the face of the tip, creating a photon trap, so all laser photons that enter the aspiration port are internally reflected and kept within the probe tip. (This arrangement also serves to unblock the aspiration port if it becomes clogged with debris.) Tissue that you wish to ablate must be positioned inside the curve of the tip so that it can be purchased with the vacuum and falls into the path of the laser.

The unique design of the phacolysis tip, with the aspiration port facing the surgeon, necessitates a change in technique. Soft lenses aspirate easily, but pre-chopping may be necessary for denser grades of nuclei.

The temperature of the probe tip does rise -- about 1° Celsius -- but the heat is rapidly removed by aspiration. In fact, the peak intensity of Paradigm's Photon system is more than ten thousand times below the level required for the onset of plasma generation (used during posterior capsulotomy). For that reason, the Photon system is an exceptionally safe modality in terms of capsular integrity. In the wet lab, using pig eyes, firing the laser repeatedly directly at the anterior lens capsule doesn't cause any discernible damage. This could make the system an important tool in refractive lens surgery.

A pilot study using the Paradigm Photon Laser System has shown promising results, and a clinical study protocol, focusing on softer grades of nuclear sclerosis, is now underway in the United States.

Outlook: promising

Because of its current limitations and the difficulties of introducing a new technology into a market that's already feeling the pinch of shrinking reimbursements, laser phaco probably won't replace standard ultrasound phaco any time soon. Nevertheless, we can expect significant advances in laser phaco in the future. It's a technology with tremendous potential.

Mark Packer, M.D., I. Howard Fine, M.D. and Richard S. Hoffman, M.D. are professors at the Casey Eye Institute at Oregon Health & Science University. Dr. Packer is clinical assistant professor of ophthalmology; Dr. Fine is clinical professor of ophthalmology, and Dr. Hoffman is clinical instructor of ophthalmology. All three are in private practice in Eugene, Oregon. Laurence Sperber, M.D., is an attending surgeon at the Manhattan Eye, Ear and Throat Hospital in New York City. He is also in private practice in New York, specializing in cornea, cataract and refractive surgery.