Comparison of erbium:yttrium-aluminum-garnet-laser vitrectomy and mechanical vitrectomy: a clinical study

OBJECTIVE: To evaluate the clinical usefulness of the erbium:YAG (yttrium-aluminum-garnet) laser for vitrectomy and to compare it with a conventional mechanical vitrectomy system regarding the intraoperative parameters. DESIGN: Prospective, randomized, clinical trial. PARTICIPANTS: Thirty eyes of 30 patients underwent vitrectomy, 15 eyes in each group. METHODS: For mechanical vitrectomy, a commercially available vitrectomy unit was used. The operating parameters, cutting rate (7 Hz = 420 cpm), maximal suction force (300 mmHg), and aspiration flow (20 ml/min), were held constant. A newly developed erbium (Er):YAG laser unit and handpiece was used for laser vitrectomy with predetermined parameters for cutting rate (70 Hz = 4200 cpm), maximal suction force (50 mmHg), and aspiration flow (20 ml/min). Surgery parameters were recorded in real time and the operation was video recorded. The clinical follow-up time was a minimum of 3 months (average, 6.2 months; range, 3-9 months). MAIN OUTCOME MEASUREMENTS: The surgery time was comparable in both groups. During Er:YAG laser vitrectomy, the average suction force was significantly reduced (P< 0.001) compared with that during mechanical vitrectomy. The mean-square variation in suction as a measure to quantify the forces acting on intraocular structures during surgery was significantly smaller in the Er:YAG laser vitrectomy group (P < 0.001). CONCLUSIONS: Erbium:YAG laser vitrectomy may provide a semicontinuous procedure. This technique minimizes periodical intraoperative forces and movements of intraocular structures and may provide, therefore, a safer vitrectomy.     

Bewegungsartefakte im Glaskörper während der Vitrektomie

Background. Movements and vibrations of intraocular structures can be observed during vitrectomy with mechanical cutting systems. We experimentally compared these intraocular motion artifacts between mechanical and erbium:YAG laser vitrectomy. Material and methods. The intraocular structures were reliably simulated by a 0.9-mm-wide foil (thickness 10 μm) in a water-filled cuvette. The movements caused by commercial mechanical cutter systems were compared with vibration induced by means of laser surgery probes (laser pulse energy 20 mJ). Laser triangulation was used to measure the movement amplitudes at various cutting rates of 2, 5, and 10 Hz and a constant suction force of 50 mmHg. Results. At all cutting rates the amplitude with the laser was less than that with the mechanical system. The ratio of the maximal amplitude between laser surgery probes (A_L) and mechanical cutter system (A_M) was A_L/A_M=0.29 at 10 Hz, A_L/A_M=0.33 at 5 Hz, and A_L/A_M=0.45 at 2 Hz. Conclusion. The reduced intraocular movements with erbium:YAG laser vitrectomy constituts a potential advantage for the nonpulsatile vitrectomy.     

Erbium:YAG-Laser Vitrektomie Erste klinische Ergebnisse

Background. Much interest has been expressed in recent years in the use of erbium:YAG lasers in ophthalmology, particularly for vitrectomy and phacoemulsification. Patients and methods. We performed 54 operations (49 primary, 5 secondary) for pars plana vitrectomy on 53 eyes of 53 patients using the Phacolase erbium:YAG laser at a frequency of 10–100 Hz single-pulse energy of 5–50 mJ. Results. The operation was successful in 51 cases, while in three we had to resort to mechanical vitrectomy due to initial technical problems. Conclusion. Erbium:YAG laser vitrectomy was generally fast and caused little mechanical stress to the retina. Complications were only those known from mechanical vitrectomy. The handpiece showed good properties for removing vitreous but not for cutting membranes, although new handpieces specifically for the cutting of membranes are under development.     

Phacoemulsification and vitrectomy with the erbium:YAG laser and phacoemulsification with the neodymium:YAG laser

There are an increasing number of possible applications for the use of Erbium:YAG and Neodymium:YAG lasers in opthalmology. Laser-phacoemulsification as well as Erbium-laser vitrectomy is of major interest. We report on the underlying technology and more than 1-year-experience using the PHACOLASE (Asclepion-Meditec, Jena, Germany, 10–100 Hz frequency, 5–50 mJ single pulse energy) for phacoemulsification and pars plana vitrectomy and the Lyla-Dodick laser photolysis (A.R.C. Laser, Eckental-Forth, Germany, 1–20 Hz, up to 8 mJ single pulse energy). The Erbium:YAG-laser as well as the Neodymium:YAG-laser enabled us to extract lenses with up to medium hard nuclei. Moreover, the Erbium laser enabled fast vitrectomy with little mechanical traction. In many of our initial surgical operations we had to change to mechanical vitrectomy due to initial technical problems. No new complications occurred intra- or postoperatively. The handpiece worked well in removing vitreous bodies, but was not feasable for cutting membranes. Modified handpieces for this purpose are under development.     

Application of erbium: YAG laser in ocular ablation

Recent developments in lasers have provided us the possibility of laser ocular surgery. The xenon, argon, neodymium:YAG and dye lasers have been successfully used in out-patient clinics. The excimer laser has been attracting researchers' interest in the new application of laser to cornea and lens. The erbium:YAG laser emits a 2.94-microns beam that can ablate the transparent ocular tissues such as lenses and corneas. The author has applied this laser to the cornea, lens, vitreous and other ocular tissues. The erbium:YAG laser beam was directed through a 1.5-meter-long, 200-microns-diameter fiberoptic guide. The radiant energy measured about 50 mJ at the end of the probe. The laser was emitted as a 400-microsecond pulse. Freshly enucleated rabbit eyes were used in this study. Laser burns were applied to the tissue surface at various energy settings. At minimal power, the tissues were coagulated by the erbium:YAG laser application. At a power of more than 636-954 mJ/mm2, tissue began to evaporate; the tissue loss was observed under a surgical light microscope. Corneal photoablation, lens ablation, iridotomy, trabeculotomy, cutting of the vitreous and retinal ablation were easily performed. Like the excimer laser, the erbium:YAG laser is a potential tool for ocular surgery.     

Zur Entstehung von Kavitationsblasen bei der Erbium:YAG-Laser-Vitrektomie

BACKGROUND: Clinical and experimental studies demonstrated the potential advantages of Erbium:YAG laser vitrectomy for posterior segment surgery. However, a detailed knowledge on the laser-tissue interaction is needed for an optimization of new ophthalmic applications. The aim of this experimental work was to investigate the cavitation bubble formation during Erbium:YAG laser vitrectomy and to find optimized laser parameters and the best geometry of the aspiration port of the microsurgical probe. MATERIALS AND METHODS: We investigated the formation of cavitation bubbles in water by high-speed photography. The output energy at the quartz tip reached up to 50 mJ and the laser pulse duration ranged from 50 to 300 microseconds. Various commercially available microsurgery probes were investigated regarding the extent of the cavitation bubbles. RESULTS: The threshold for laser-induced cavitation bubble formation was found to be 0.32 +/- 0.1 mJ for a laser pulse duration of 130 microseconds and a core diameter of 320 microns of the quartz fiber tip. The length of the cavitation bubbles increases with the laser pulse energy up to a length of 1.6 mm at a pulse energy of 10 mJ. In contrast, the size of the vapor bubbles decreases with an increase of the laser pulse duration. A slit-shaped aspiration port led to a 50% smaller volume of the cavitation bubble exiting the port compared with a circular aspiration port. CONCLUSIONS: The optimized laser parameters and microsurgery probe geometry may significantly decrease the risk of intraoperative ocular damages during Erbium:YAG laser vitrectomy.     

A new and improved vitreoretinal erbium:YAG laser scalpel: long-term morphologic characteristics of retinal-choroidal injury.

BACKGROUND AND OBJECTIVE: To report a modified erbium:YAG laser scalpel designed to incise tissue more efficiently and safely than other systems reported to date. MATERIALS AND METHODS: An erbium:YAG laser delivery system was built to deliver laser energy in bursts of micropulses with a repetition rate of 1,000 Hz. The laser was coupled to handpieces with tip designs equipped with shields, backstops, and beveled, straight, and flexible fibers. In vivo studies in the rabbit eye were performed to determine damage threshold, optimal pulse energy, and burst frequency required to make incisions in the retina and choroid. The safety profile and directional control provided by the handpieces were tested for consistency. Partial- and full-thickness retinal-choroidal incisions were examined clinically and histologically at various time intervals. RESULTS: The best incisions were obtained at a fluence of 3.5 J/cm2 or greater, a burst repetition rate of 10 to 40 Hz, and 6 micropulses per burst. Retinal damage occurred when incising laser energy was used 500 microm or closer to the retinal surface. Depth of penetration of laser energy did not depend on burst repetition rate. The use of laser endoprobes equipped with shields and backstops provides absolute protection from stray laser energy in aqueous media. The use of flexible beveled fiber tips provides reliable, accurate directional control. Retinal-choroidal incisions and damage resulted in local retinal-choroidal degeneration and adhesion formation. CONCLUSION: The modifications to the erbium:YAG laser scalpel provide a more efficient, versatile, and safe application to vitreoretinal surgery than any system reported to date.     

Erbium-YAG laser-assisted preparation of deep sclerectomy

Background: Deep sclerectomy and viscocanalostomy are becoming more and more popular as non-penetrating filtering procedures. The purpose of the present study was to simplify the technique of this procedure and to reduce the rate of unintended perforations during the preparation of the deep lamella. Methods: 20 enucleated porcine eyes were used. A superficial lamellar scleral flap with an area of 5×5 mm as for trabeculectomy was surgically prepared. Using a pulsed erbium:YAG laser the deep lamella (220±40 μm) with an area of 4×3 mm was removed. Ablation was performed with an energy of 40–100 mJ, a frequency of 1–10 Hz and a spot size of 500 μm and 1 mm (divergent beam). During the procedure the intraocular pressure was kept constant by continuous infusion. Finally the eyes were analyzed histologically. Results: After initial trials it was possible to ablate the remaining deep corneoscleral lamella with the erbium:YAG laser without perforating into the anterior chamber. Starting with an energy of 70–85 mJ and a reduction to 40–60 mJ when reaching deeper layers, a spot size of 500 μm and a 10 Hz repetition rate gave the highest safety and efficiency in preparation. After a learning curve it was possible to preserve Descemet’s membrane and intact trabecular meshwork in 10 consecutive operations as demonstrated by histology. Conclusion: Erbium:YAG laser- assisted deep sclerectomy offers an alternative to microsurgical preparation of the deep scleral lamella. The thermal damage is minimal (10–40 μm) and scarring may therefore not be stimulated. Received: 3 January 2000 Revised: 3 April 2000 Accepted: 10 April 2000     

Erbium laser phacoemulsification--a clinical pilot study]

INTRODUCTION: From August 1997 to March 1998, we performed a prospective pilot study to examine erbium laser phacoemulsification in cataract surgery under clinical conditions and to determine the side effects of this method. PATIENTS AND METHOD: 34 patients (40 eyes) with senile cataract were recruited. Slit lamp findings, keratometry, best corrected visual acuity, refraction, pachymetry, endothelial cell count and intraocular pressure were determined preoperatively and on 1st, 4th, 14th and 60th postop day according to a standardised protocol (single pulse energy between 10 and 20 mJ, frequency of application 60 Hz, average phaco time 3 min, total energy 38.5 mJ). The operations were done with the erbium laser system MCL 29, Aesculap-Meditec Co., Jena, Germany. RESULTS: A total emulsification of the nucleus was possible in 36 of 40 eyes (90%) (nucleus hardness between 0 and 3). A partial emulsification of the nucleus in nucleus hardness 3 was possible in 2 eyes, in nucleus hardness 4 in 1 eye and in nucleus hardness 2 in 1 eye (4 eyes--10%). Visual acuity increased from 0.3 preop to 0.8 two months postop (median). Intraocular pressure decreased from 16 mm Hg preoperatively to 13 mm Hg two months postoperatively (median). The increase of corneal thickness was not statistically significant compared to baseline. The decrease of endothelial cell count was 0.96%. Postoperative complications which are not known in ultrasonic phacoemulsification did not appear in erbium laser phacoemulsification. CONCLUSION: Erbium laser phacoemulsification is a surgical method that makes the emulsification of softer nuclei under clinical conditions possible with a low rate of complications also in the beginning of the learning curve. For higher nucleus hardnesses, technical and surgical parameters have to be optimised. Advantages of erbium laser phacoemulsification compared to ultrasonic phacoemulsification are less energy transmission into the eye, no heating of anterior chamber, impossibility of corneal burns and easier access in eyes that are deep into the orbit. Especially advantageous is the high protection of endothelium by erbium laser phacoemulsification. A prospective controlled comparative study to ultrasonic emulsification is desirable.     

Ablation of vitreous tissue with a high repetition rate erbium:YAG laser

PURPOSE: To quantify erbium (Er):YAG laser ablation of vitreous in relation to different pulse repetition rates < or = 200 Hz, in order to examine the feasibility of laser for removal of vitreous gel (photovitrectomy) in clinically acceptable times. METHODS: Fresh porcine vitreous samples and saline controls were ablated in air with an Er:YAG laser connected to a sapphire fiber at pulse energies between 1.0 and 21.2 mJ and at pulse repetition rates between 10 and 200 Hz. Net ablation rates were determined by weight measurement. RESULTS: Reproducible and constant ablation rates were found for given laser parameters. Net ablation rates increased linearly with pulse repetition rate and nonlinearly with pulse energy. Expanded laser parameter domains permitted vitreous ablation rates as low as 1 microg/s to as high as 1031 microg/s. Ablation rates did not differ significantly between vitreous and saline. CONCLUSIONS: The study documents clinically useful vitreous ablation rates that scale linearly with high repetition rates of Er:YAG laser, and suggests directions for further development of laser technology for enhanced removal of vitreous and other tissues. However, nonlinear effects of pulse energy also exist, indicating need for careful examination of ablation characteristics in various instruments.     

Erbium:YAG laser cataract removal: role of fiber-optic delivery system

PURPOSE: To review the properties of energy delivery systems and to evaluate the efficiency of zirconium-fluoride-based and sapphire fibers delivering erbium:YAG (Er:YAG) laser energy in a clinical laser cataract surgery system. SETTING: Department of Ophthalmology, Medical College of Virginia Campus of Virginia Commonwealth University, and Veterans Affairs Medical Center, Richmond, Virginia, USA. METHODS: Thirty-two patients had Er:YAG laser cataract extraction. Preoperative visual acuity ranged between finger counting and 20/40 secondary to cataract. The endothelial cell count was measured preoperatively and 6 weeks after surgery. A zirconium-fluoride-based fiber was used in 23 patients and a sapphire fiber in 9 patients. RESULTS: Of the patients examined after 3 months (n = 31), 90.3% (n = 28) had a visual acuity of 20/30 or better and 9.7% (n = 3), of 20/40 or 20/50. Mean endothelial cell loss at 6 weeks was 7.6% +/- 12.8 (SD). Posterior capsule rupture with vitreous loss occurred in 3 cases; 1 was attributed to laser damage to the capsule. Conversion to ultrasound phacoemulsification was required in 13 cases. Suitable fiber materials for Er:YAG laser delivery are sapphire, zirconium fluoride, silica, and germanium oxide. Toxicity of the latter is under investigation. CONCLUSION: The Er:YAG laser emulsified the lens nucleus safely and effectively. These early results include a higher than acceptable posterior capsule rupture rate and reflect the surgeon's learning curve with a new technology. Effective power delivery can be achieved with sapphire- and zirconium-fluoride-based fiber optics through a silica tip. The optimal energy delivery system has not been determined.     

Applications of combination wavelength (1060-nm and 530-nm) and pulsed Nd:YAG laser for contact laser surgery

Two pulsed neodimium yittrium aluminum garnet (Nd:YAG) laser systems were evaluated for contact surgery through a fiberoptic system with a sapphire tip. Pulsed Nd:YAG laser at 1060 nm was as effective as continuous-wave Nd:YAG laser in producing tissue incisions. A combination of 1060-nm and 530-nm wavelengths achieved smooth cutting at lower energy levels. Corneal endothelial cell damage occurred at the high power level (7 watts) required for smooth underwater incisions with both continuous wave and pulsed lasers.     

晶状体后囊皱褶Nd：YAG激光切开术

目的探讨Nd：YAG激光晶状体后囊皱褶切开术的效果。方法晶状体后囊皱褶33例（33眼）。术前爱尔卡因表麻下置CGP角膜接触镜，借助瞄准光，准确聚焦于皱褶上，发射Nd：YAG激光，单脉冲切开皱褶能量为0．4～1．0mJ，每次治疗总量为20—30mJ，平均（25±0．12）mJ。结果后囊皱褶激光切开术后矫正视力：1．0者22眼占66．67％，0．6—0．8者7眼占21．21％，0．5—0．7者4眼占12．12％。裂隙灯显微镜下观察未发生人工晶状体损伤，无玻璃体疝、黄斑囊样水肿或视网膜脱离等并发症。结论用Nd：YAG激光切开晶状体后囊皱褶，可增进视力，疗效良好。     

Erbium: YAG-Laser Vitrektomie Temperaturmessungen in unterschiedlichen Austauschmedien

BACKGROUND: The erbium:YAG laser has the potential of being used routinely for vitrectomy because of the excellent quality of liquefying vitreous structures and the low vacuum forces required. However, the use of silicone oil and perfluorocarbon may lead to unwanted temperature increases in the microsurgery probe. The aim of this work was to investigate this side effect. MATERIALS AND METHODS: Different replacement materials such as water, methocel, silicone oil and perfluorocarbon were used in a simple eye model. The temperature increase during laser application was measured by means of thermocouples. The maximum temperature increase and time decay were derived with and without aspiration from these time-resolved measurements. The average power at the distal end of the microsurgery probe was chosen to be 1 W. RESULTS: The temperature increase with aspiration in water was found to be significantly smaller than all other replacement materials. Interruption of aspiration leads to a critical temperature increase of approximately 14 K; however, this increase occurred very slowly (decay time 200 s). A comparable result could be observed for methocel, which was used to simulate condensed vitreous structures. In perfluorocarbon and silicone oil we measured a far higher increase in temperature of up to 130 K within a few seconds. Furthermore, small remnants of carbonized materials can be seen in the microsurgery probe after laser application. CONCLUSIONS: The temperature increase during erbium:YAG laser vitrectomy in water can be considered to be harmless for other intraocular structures. However, insufficient aspiration or increased vitreous condensation leads to increased temperature in the microsurgery probe. Our results demonstrate that the use of erbium:YAG laser vitrectomy in materials such as silicone oil or perfluorocarbons is contraindicated.     

钇铝石榴石激光治疗白内障摘除术后并发症的临床研究

目的探讨白内障摘除术后钇铝石榴石(yttriumaluminumgarnet,YAG)激光的应用范围,激光后囊膜切除术的方法、疗效和并发症.方法超声乳化白内障吸除人工晶状体(intraocularlens,IOL)植入手术4600只眼,术后YAG激光治疗451只眼,其中行后囊膜切除380只眼,切除方法采用连续环状切开及后推膜瓣二步法;连续环状切开时平均单脉冲能量为(1.21±0.31)mJ,平均总能量为(52.44±14.62)mJ;后推膜瓣时平均单脉冲能量为(2.12±0.43)mJ,平均总能量为(50.88±10.32)mJ.IOL前膜切除42只眼,脉冲能量为1.0～1.4mJ,平均总能量为(56.28±32.74)mJ.治疗其他术后并发症29只眼.结果白内障摘除术后行YAG激光治疗451只眼(9.8%).后囊膜切除手术率为8.3%;1次激光手术成功率为96.3%;平均裸眼视力提高0.26,矫正视力为0.85;未出现明显的IOL损伤和移位;362只眼(95.3%)眼压正常;2只眼视网膜脱离.结论YAG激光无需切口可在眼内完成精确的分割手术,且操作方便、安全,疗效好、并发症少、应用范围广.     

Erbium:YAG-Laser-Phakoemulsifikation Vergleich von 2 verschiedenen Applikationssystemen

Background. The erbium:YAG laser a suitable energy source for photoablation of several tissues with only minimal thermal side effects. The application system is an important factor in increasing its efficiency. Materials and methods. We used an Er:YAG laser designed for clinical application. The energy was guided via a special coated zirconium fluoride fiber to handpieces of various designs. Twenty lenses of patient eyes were treated using two application systems with 0° and 30° tips. Results. Despite similar cataract density an average laser phacoemulsification took significantly less energy and less time using the 0° tip. Conclusions. Use of the Er:YAG laser is superior to ultrasound phacoemulsification in minimizing thermal energy required for lens removal. Certain parameters of the application system construction, in this case the 0° tip, can provide additional efficiency. Further developments should pay attention to these findings.     

Nd:YAG激光松解切开术治疗晶状体后囊膜皱褶

目的:探讨Nd:YAG激光松解切开术治疗晶状体后囊膜皱褶的效果。方法:术前爱尔卡因表面麻醉下置CGP角膜接触镜,借助瞄准光,准确聚焦于皱褶上,发射Nd:YAG激光,单脉冲松解皱褶能量为0.4～1.0mJ,每次治疗总量为20～30(平均24.00±0.0625)mJ。结果:后囊膜皱褶激光松解切开术后矫正视力1.0者31眼(58%),0.6～0.8者17眼(32%),0.4～0.5者5眼(9%)。裂隙灯下观察未发生人工晶状体损伤,无玻璃体疝、黄斑囊样水肿或视网膜脱离等并发症。结论:用Nd:YAG激光松解切开术治疗晶状体后囊膜皱褶,可增进视力,疗效良好。     

Sclerostomy with an Erbium YAG Laser. The Relationship with Pulse Energy

Purpose: To investigate the optimal pulse energy to do sclerostomy with an erbium YAG laser.Materials and Methods: The experiments were performed in enucleated porcine eyes. We changed pulse energy and examined the effects on surrounding tissue.Results: With the increase of pulse energy, the effects of the laser extended to the area surrounding the laser probe. At the threshold energy for doing full-thickness sclerostomy, the total energy was significantly higher than with higher pulse energy. And with pulse energy higher than 2 mJ, the total energy did not show any significant change. Histopathologically, the damaged area around sclerostomy became larger with the increase of pulse energy.Conclusion: The optimal energy to do full-thickness sclerostomy with this system seemed to be 2 mJ.     

Sclerostomy with an erbium YAG laser--the relationship with pulse energy

PURPOSE: To investigate the optimal pulse energy to do sclerostomy with an erbium YAG laser. MATERIALS AND METHODS: The experiments were performed in enucleated porcine eyes. We changed pulse energy and examined the effects on surrounding tissue. RESULTS: With the increase of pulse energy, the effects of the laser extended to the area surrounding the laser probe. At the threshold energy for doing full-thickness sclerostomy, the total energy was significantly higher than with higher pulse energy. And with pulse energy higher than 2 mJ, the total energy did not show any significant change. Histopathologically, the damaged area around sclerostomy became larger with the increase of pulse energy. CONCLUSION: The optimal energy to do full-thickness sclerostomy with this system seemed to be 2 mJ.     

The experimental study of Nd: YAG laser injuring effects on intraocular lenses made by different materials

OBJECTIVE: To inquire the injuring effects of the Q-switched neodymium: yttrium aluminum garnet (Nd : YAG) laser on silicone, hydrogel (HEMA), acrylic, lathe cutting and cast molding polymethylmethacrylate (PMMA) intraocular lenses (IOLs). METHODS: The Nd : YAG of different energy was focused on the posterior surface of the IOL optic portion and shot in air and BSS separately. The percentages of IOL injuries were calculated, and the morphology of the IOL injuries was observed with a scanning electron microscope. RESULTS: Percentages of IOL injury: When the same energy of Nd : YAG laser was used, the injuring effects on the same kind of IOLs in air and in BSS were similar, while the laser energies of 0.5 mJ and 1.0 mJ were used, the injuring effects on different kinds of IOLs were significantly different, and when the energy of the laser was more than 1.5 mJ, the injuring effects were almost the same. Under different conditions, the morphology of the injury on different kinds of IOLs was different. CONCLUSIONS: (1) The sequence of resisting ability against Nd : YAG laser injury of different kinds of IOLs from strong to weak is: The lathe cutting PMMA IOL > acrylic IOL > cast molding PMMA IOL > HEMA IOL and silicone IOL. (2) The injuring effect of high energy Nd : YAG laser on rigid IOL is more severe than that on the soft IOL. (3) The size of IOL injuries is increased with the elevation of energy level of Nd : YAG laser.