Laser Cataract Surgery: Technique and Results

Just as cataract surgery is the most common intra-ocular surgery, ultrasound phacoemulsification is the preferred technique among cataract surgeons.1 However, despite the improvements surgeons have made to this technique, there are still many issues we must address in order to improve its success rate. The most negative facet of ultrasound phacoemulsification is the way in which it increases the anterior chamber temperature. This can cause an inflammatory response and also creates the risk of injury over the incision and to the intracameral structures, corneal endothelium, iris, and posterior capsule.2 The incision size is another issue to consider for ultrasound phacoemulsification; while it now achieves incisions as small as 2.5 mm, they have not reached the 0.8-mm size that the laser allows.3 This is significant in light of the newly introduced IOLs that can be implanted through incisions that are 2 mm and smaller.4

DIFFERENCES BETWEEN LASERS
Researchers have tried to find solutions to the drawbacks of ultrasound phacoemulsification by developing different types of lasers. The studies in this field are currently focused on using the infrared wavelength, particularly the Er:YAG laser (wavelength 2,940 nm) and the Nd:YAG laser (wavelength 1,064 nm). The principal difference between these two lasers is the degree to which their energy is absorbed by water, which determines how they function. Water will absorb the energy of the Er:YAG laser nearly 100% but will absorb very little of the Nd:YAG laser's energy. The surgeon can therefore focus the Er:YAG laser beam directly over the cataract, because the high water content of the surrounding tissue shields it from beam injuries.5 The Nd:YAG laser beam, however, may not be totally absorbed at the cortex of the nuclear material and may damage adjacent structures. To avoid further injury with the Nd:YAG laser beam, surgeons must design a “closed” terminal to accommodate the cortical and nuclear fragments. Thus, the laser beam can act selectively and avoid an uncontrolled beam projection. For this reason, lasers such as the Nd:YAG are known as lasers of indirect action.5-10

In this study, we assessed the efficacy and safety of cataract surgery performed with an Er:YAG laser using a handpiece specially designed for this surgery and a modified fluidic appropriate to fulfill all the surgical requirements. This surgery, although similar to that performed with ultrasound, has slight differences.

SURGICAL TECHNIQUE
We performed the laser surgical procedure with the Phacolase (Carl Zeiss Meditec AG, Jena, Germany). We connected the Phacolase to an optical fiber made of zirconium fluoride, a nontoxic biocompatible quartz tip, and the fluidics from the Sovereign phacoemulsification system (Allergan, Inc., Irvine, CA). The procedure began with one 1.2-mm incision in the temporal cornea and another 1-mm corneal incision placed at the 2-o'clock position. Through the first incision, we inserted one needle of the handpiece together with the optical fiber connected to the aspiration system. We introduced the chopper, which featured an irrigation system specifically designed for this procedure (Figure 1), through the smaller incision. The laser needle had an external diameter of 0.9 mm and an internal diameter of 0.7 mm. We modified the needle's opening to facilitate aspiration of the cortical fragments, and we did not need to change the probe to an I/A tip, as is usually necessary with the ultrasound procedure. We placed the 200-µm-diameter optical fiber inside the phaco needle, 0.5 mm from the needle's opening (which differs from procedures to date), to facilitate suctioning the cataract fragments and to improve the efficacy of the emulsification.

The surgical maneuvers necessary with the chopper differ from those usually performed with ultrasound. Considering that the laser needle cannot fix the lens material as in ultrasound procedures, the surgeon must pass the chopper underneath the nucleus and press it against the phaco tip located in the anterior surface of the cataract to achieve nuclear fracturing (Figure 2). This maneuver may be repeated as many times as needed. In our experiment, we attempted to fragment the nucleus into six or more pieces in order to reduce the final energy. At this stage, an accurate hydrodynamic system is essential to produce higher vacuum levels that will keep the fragments attached to the needle's tip during emulsification. We used the Sovereign fluidic system and adjusted the parameters for every case based on the density of each cataract. We performed the capsulorhexis, IOL implantation, and incision closure in the same manner as during the ultrasound procedure.

PATIENTS AND METHODS
We studied 147 eyes of 129 consecutive patients. The patients were divided into two groups, according to the surgical procedure. These groups were classified further into four levels, depending on the density of their cataracts (cataracts marked with one cross, indicating level 1, showed minimal nuclear sclerosis; those marked with four crosses, indicating level 4, showed maximum sclerosis; Table 1).

One group of patients underwent cataract surgery performed with the Acurus ultrasound system (Alcon Laboratories, Fort Worth, TX), and the other group underwent surgery using the Phacolaser. All patients underwent full ophthalmologic and systemic examinations. In all cases, we performed ultrasonic biometry or interferometry and implanted the eyes with an SI40 IOL (Allergan, Inc.) or a Stabibag (IOLTECH Laboratories, La Rochelle, France). All surgical procedures included topical anesthesia and intravenous sedation. The preoperative topical treatment consisted of norfloxacin, mydriasis, and periocular asepsis with 5% Betadine (Purdue Pharma L.P., Stamford, Connecticut). Postoper-atively, we administered topical antibiotic anti-inflammatory agents (norfloxacin and fluorometholone) for 1 week.

We performed the laser surgical procedure using the Phacolase with the technique previously described. We conducted the endothelium study using the endothelial microscope (Topcon SP-2000P; Topcon America Corp, Paramus, NJ) and analyzed the cells postoperatively at 1, 3, and 6 months. The Pocket Pachymetry (Quantel Medical, Les Ulis, France) supplied us with preoperative pachymetry, as well as postoperative data at 3 and 7 days and at 1, 3, and 6 months. We determined IOP values by applanation tonometry both preoperatively and at 3 and 7 days and 1, 3, and 6 months postoperatively. The Alpins vector analysis (ASSORT Pty. Ltd., Victoria, Australia) helped us to analyze likely astigmatic changes.11 We also conducted a fluorescein angiography 5 weeks postoperatively to evaluate the posterior segment.

CLINICAL RESULTS
Table 1 shows the IOP values, surgical times, and average changes in the endothelial pachymetry and cell counts for the studies conducted. Analysis showed a slight reduction (-0.8%) of the IOP values at 7 days in the patients treated with ultrasound. Additionally, we found no differences among the four levels of cataract density (P<.01) for the ultrasound patients. However, we found differences in patients treated with laser between cataract density levels 1 and 2 compared with levels 3 and 4 (P<.001). The patients with level 1 and 2 cataracts who were treated with laser were similar to those treated with ultrasound (P>.01), but patients with level 3 and level 4 cataracts had an IOP increase of 12.6 ± 3.55% and 18.2 ± 2.62%, respectively. These values returned to normal after adjusting the medical treatment, and after 3 weeks only one patient with ocular hypertension continued to receive medical treatment (for 2 months).

One factor that was particularly interesting was the surgical trauma related to the length of the surgery—specifically, the hydrodynamic flow level in the anterior chamber. Table 1 shows the values of the surgical time related to the intraocular irrigation.

Table 1 also shows variations in the endothelial cell count. The values include the percentage changes from the preoperative examinations and follow-up visit at 3 months. There was a slight reduction in cell numbers in all cases. In the patients treated with ultrasound, the average decrease was 2.8% and ranged from 2.4% (level 1 cataracts) to 3.2% (level 4 cataracts). There were similar values in the group treated with laser in cataract levels 1, 2, and 3, with no significant differences between both groups (P>.01). However, there was a significant reduction in the number of endothelial cells in the patients with level 4 cataracts, (13.4%), compared with the patients with level 4 cataracts treated with ultrasound (3.9%) at 12 months postoperatively.

The pachymetry study at 7 days postoperatively showed stable values in the group treated with ultrasound (Table 1), with no significant percentage difference compared to the hardest level 4 cataracts (P<.01). The group treated with laser followed the same trend as the other parameters. The pachymetry values returned to normal at the 2-month follow-up visit, except in two patients who had irreversible edema. A therapeutic contact lens was a partial solution for one patient; however, the other patient required a corneal transplant.

There was a significant difference in visual recovery in patients with level 3 and 4 cataracts (P<.001 and P<.0005, respectively). At the 6-month follow-up visit, the patients with level 3 cataracts who were treated with laser achieved good BCVA (0.84), as did the patients treated with ultrasound, (0.87, P>.01). However, the patients with level 4 cataracts who were treated with laser maintained a low BCVA level (0.53), compared to the patients treated with ultrasound, (0.84, P<.0005).

COMPLICATIONS
In the group of patients treated with ultrasound, there was only one case of subclinical cystoid macular edema (CME), diagnosed by fluorescein angiography. In the group treated with laser, there were seven cases of CME, five of which were subclinical and two of which resulted in a visual reduction that returned to normal levels after topical treatment. In the group treated with laser, there were two cases of irreversible corneal edema, in which one patient required a corneal transplant. Three cases of posterior capsule rupture required an anterior vitrectomy, and four cases required conversion to the ultrasound procedure.

DISCUSSION AND CONCLUSIONS
We prefer the Er:YAG laser, which uses maximal water absorption, because erbium radiation is absorbed better at all fluencies than other types of radiation. This laser has a short penetration depth of 1.0 µm that produces a small volume of ablated tissue, thus improving efficacy and minimizing the thermal effects.2,12,19-25 In addition, the Er:YAG laser has a lower ablation threshold and a greater photovaporization rate than other infrared systems such as Nd:YAG.24 The Er:YAG laser ablates lens material directly, which may be more effective than disrupting lens material indirectly (this occurs with the Nd:YAG laser, which uses a target or photofragmentation chamber).26 In addition, erbium radiation is not mutagenic or carcinogenic.12,27

The results obtained in this study differ in some aspects from the high satisfaction shown in previous studies of cataract surgery with laser.3-9,28 In our study, we observed that with level 1 and 2 cataracts, the data were similar for both ultrasound and laser. The difference between the two groups appears with level 3 cataracts and becomes more evident in cases of level 4 cataracts, where we find patients with complications that do not allow a complete visual recovery.

More investigation is needed to improve the technical conditions that help to create greater efficacy and safety when removing the hardest cataracts, which require a longer surgical time.
Carlos Vergés, MD, PhD, is Professor of Ophthalmology and Head of the Department of Ophthalmology at the Institut Universitari Dexeus in Barcelona, Spain. He may be reached at cverges@cverges.com.
Elvira Llevat, MD, practices at the Institut Universitari Dexeus in Barcelona, Spain. She may be reached at marin@cverges.com.
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