Article Date: 2/1/2009

Recent Advances in 532 nm Green Laser Technology and Probe Enhancement: PUREPOINT® Pre-Clinical and Clinical Assessment

Recent Advances in 532 nm Green Laser Technology and Probe Enhancement: PUREPOINT® Laser Pre-Clinical and Clinical Assessment

TIMOTHY G. MURRAY, MD, MBA, FACS, · AMY C. SCHEFLER, MD, · YOLANDA PINA · ELEUT HERNANDEZ

Intraoperative endophotocoagulation has revolutionized the surgical management of patients with complex vitreoretinal pathology. Traditionally, chorioretinal adhesions were obtained through the use of diathermy, cryotherapy, or post-operative transpupillary laser. Early work by Smiddy and colleagues noted the enhance characteristics of chorioretinal adhesions obtained by laser energy delivery as compared to cryoablation. Blumenkranz and colleagues have focused on specific tissue targeting using alterations in the parameters of pulse duration, laser power and spot size. Charles first reported the application of Xenon light endophotocoagulation in 1979. This technology was complicated by inherent limitations in the Xenon photocoagulator with high propensity to induce iatrogenic retinal breaks.

Rapid deployment of the argon laser endophotocoagulator in the early 1980s greatly improved the therapeutic treatment window by enabling the endolaser probed to be moved further from the retina surface (typically 0.1mm for Xenon and 3.0 mm for Argon). Argon laser photocoagulation (blue-green 488 nm, green 514.5 nm) was possible through vitreous, fluid and various intraocular gases without degrading the quality of the laser burn. Puliafito and colleagues introduced an intraocular diode laser employing semiconductor technology to deliver an 810 nm laser spot. These devices improved portability, durability and dependability of the laser system. Smiddy and colleagues reported both pre-clinical and clinical evaluation of this near-infrared laser system documenting different clinical characteristics of burn production.

For the retinal surgeon, as important as the laser system itself, the delivery methodology is critical. Typically intra-operative laser has been delivered with endo-laser probe application. Over the last decade, surgeons have incorporated indirect ophthalmoscopic transpupillary laser into their armamentarium for intra-operative laser photocoagulation.

Timothy G. Murray, MD MBA FACS is Professor of Ophthalmology and Radiation Oncology at Bascom Palmer Eye Institute, University of Miami Miller School of Medicine. Dr. Murray is a consultant for Alcon Laboratories, Inc., Fort Worth, Texas.

Amy C. Schefler, MD, Yolanda Pina and Eleut Hernandez are affiliated with Bascom Palmer Eye Institute, University of Miami Miller School of Medicine.

LASER FUNDAMENTALS

LASER, Light Amplification by Stimulated Emission of Radiation, is typically produced by a three component system incorporating a material to store energy released by stimulated emission, a mechanism for replenishing energy within the lasing material, and a method to retain energy to stimulate further emission. Typically lasing mediums can be gas, liquid or solid. They are pumped by pulsed or continuous discharge lamps, electric discharge, electron beam, laser induction by an independent laser or direct conversion of electric current into photons within a semi-conductor. Finally, laser pulsing techniques enable pulse durations to vary from continuous to femtosecond applications.

The eye is a unique organ system for laser delivery. Endolaser photocoagulation and laser indirect ophthalmology typically achieve their effects through induction of thermal tissue necrosis achieving target tissue temperatures over 60° centigrade. This suprathreshold thermal process is influenced by three major parameters for each unique laser wavelength: power, duration, and spot size.

Lasers have evolved as the preferred light source (solar source Meyer-Schwickerath, Xenon arc lamp) for retinal photocoagulation due to collimation, brightness, and cohesiveness.

PUREPOINT® 532 nm THIN DISC LASER

Recent introduction of the CONSTELLATION® Vision System from Alcon Surgical (Fort Worth, Texas) has re-focused the key clinical features of intra-operative laser treatment. The PUREPOINT® 532 nm Thin Disc Laser is available directly embedded into the CONSTELLATION® Vision System or as an independent stand-alone laser platform. Several features of this technology are uniquely configured to enhance intra-operative laser delivery targeted to increase surgeon control and enhance patient safety. Unique manufacturing processes and engineering design strategies were employed to improve the long-term stability of the laser platform.

INTEGRATED LASER DESIGN

Four key features significantly improve the employment of this laser system.

Feature 1: From a surgeon's standpoint, the integration of a multi-function foot pedal shifts laser control from the circulating nurse to the surgeon. The multi-function foot pedal incorporates surgeon activation of the laser from standby to active, and enables surgeon control of laser power.

Feature 2: To further take advantage of surgeon control of laser activation and power, the system integrates voice confirmation technology that verbally acknowledges change in laser status (active, standby) and alteration in laser power selection. This feature allows the surgeon to continue laser treatment with control of these parameters without having to move from the surgical microscopic field.

Feature 3: RFID technology (ENGAUGE®) utilizes radio frequency identification devices to recognize the employed laser probe or laser indirect ophthalmoscope. This RFID technology uniquely pre-populates the laser treatment parameters for the selected probe. These settings can be personalized to the surgeons preference of initial laser settings for each unique device. This technology assures rapid setup of the laser.

Feature 4: The PUREPOINT® system includes two switched laser ports enabling the system to be setup for both endolaser photocoagulation and laser indirect ophthalmoscopy. This dual port feature enables single switch activation from one port to another and incorporates RFID recognition of each port. The surgeon can now seamlessly move from endolaser photocoagulation to laser indirect ophthalmoscopy with no need for transitional setup of the laser greatly facilitating operating room efficiency.

PLATFORM STABILITY

The PUREPOINT® 532 nm Thin Disc technology incorporates several design concepts that have direct impact on safety, portability and reliability of the system. Key concerns with laser delivery are related to lens focusing and thermal stability. The PUREPOINT® system incorporates a fixed design platform that enhances stability of the laser by hard manufacturing the lasing system. This essentially eliminates the potential to misalign the laser system through accidental damage to the unit. This stability also improves the thermal reliability of the system. Thermal lensing effects lead to laser energy loss through deformation of the focusing system. These effects are minimized with the thin disc technology incorporated into the PUREPOINT®. These advances in technology have delivered a remarkably stable, reproducible and surgeon responsive laser delivery system specifically targeted to intraoperative laser delivery and uniquely incorporated into the CONSTELLATION® Vision System.

ENGAUGE® RFID technology recognizes laser probe or laser indirect ophthalmoscope.

PUREPOINT® utilizes voice confirmation technology that verbally acknowledges changes in laser status.

LASER INTERFACE – PROBE DESIGN

The interface between the laser and the patient is the surgeon's choice of endolaser probe or laser indirect ophthalmoscope. Advances in laser probe technology have shifted to micro-incisional vitrectomy approaches including 25- and 23-gauge probes able to deliver reproducible and accurate laser burns indistinguishable from standard 20-gauge laser probe technology. Major advances in laser technology have moved from smaller instrument design to incorporation of design elements to enhance laser burn delivery in complex surgical case management. Curved laser probe delivery enhances peripheral laser, minimizes potential lens compromise in the phakic eye, and allows far peripheral laser delivery without the need for scleral depression. This probe technology is particularly valuable in conjunction with wide-field viewing systems and have markedly improved completion of laser treatment during the surgical procedure.

PRE-CLINICAL EVALUATION

Pre-clinical evaluation of the PUREPOINT® 532 nm thin disc laser was performed at the McKnight Vision Center of the Bascom Palmer Eye Institute. This study evaluated the impact of laser energy delivery modulation through alterations in pulse duration and power delivery utilizing pigmented Dutch Black rabbits. This study was targeted to evaluate laser burn characteristics utilizing in vivo OCT imaging and histopathology. We hypothesized that alterations in energy delivery would specifically target tissues at the retina/RPE and choroid. Previous laser studies have noted rapid increase in chorioretinal adhesion immediately post laser application and rapid modulations in the retina microenvironment including changes in cytokines, hypoxia induced factors and VEGF. These changes can be targeted with alterations in laser delivery that are amenable to surgeon control particularly spot size, power and pulse duration. Blumenkranz and others have noted that short pulse durations may specifically limit retinal/choroidal damage while Smiddy and others have suggested that longer pulse durations may enhance chorioretinal adhesion.

To evaluate the application of the PUREPOINT® laser system we employed a 23 gauge MIVS surgical system to deliver laser burns incorporating the straight 23 gauge endolaser probe. Laser was delivered in a 5 × 5 treatment box with laser parameters at clinically relevant settings including a 300 micron spot size (fixed by the surgeon) and varying pulse duration and power. Pulse duration was varied from 0.1 to 0.8 ms with fixed power, while power was varied from 200 to 1000 mW with fixed pulse duration establishing the treatment box. All animals underwent pre-treatment clinical evaluation and imaging. Animals were then serially evaluated post laser application, OCT imaging and histopathology were then obtained at 72 hours after retinal laser treatment. OCT imaging was obtained with an animal adapted research OCT 2 system consisting of an X-Y galvanometer optical scanner coupled through a 60D Volk lens (Volk Optical Inc., Mentor, OH). The power of sample light for the OCT imaging was lowered to 750 μW to ensure that the light intensity delivered to the eye was safe to the retina. The calibrated Axial Resolution was ~4 μm in air, corresponding to ~3 μm in tissue (refractive index of retina is ~1.35). Fundus imaging was obtained with a RETCAM system (Clarity). Animals were euthanized and eyes were flash frozen for immunohistochemistry and histopathology. Laser burns were reproducible, rapidly delivered and titratable. OCT documented increasing thermal injury associated with both increasing laser power and pulse duration. Lesion size increased with a titratable gradient associated with pulse duration and laser power. Micropulse delivery showed preferential tissue targeting with focused thermal effects.

CLINICAL EVALUATION

Clinical evaluation of both the stand-alone and CONSTELLATION® Vision System integrated PUREPOINT® laser were performed at the Anne Bates Leach Eye Hospital of the Bascom Palmer Eye Institute. Both the stand-alone and integrated systems were intuitive in setup, rapid in powerup, and enhanced by the RFID probe recognition. Activation of the laser through the multi-function foot pedal and variance of laser power was directed solely by the surgeon. Voice confirmation was effective but not obtrusive during the surgical procedures. Surgically 23 gauge MIVS straight, curved, and illuminated laser probes were employed without difficulty with immediate recognition and pre-population of laser setting configured by the RFID interface. Uniquely, surgeon control of the laser system allows for enhancement of patient safety by shifting the modulation of key laser parameters to the surgeon thereby enhancing a safety window for both the patient and OR team.

IMPRESSIONS

The PUREPOINT® 532 nm thin disc laser photocoagulator system, either as a stand-alone or uniquely integrated into the CONSTELLATION® Vision System, delivers reproducible, targeted, precise retinal laser energy to achieve immediate chorioretinal adhesion or to modulate tissue microenvironment. The high energy capacity, multiple mode settings, micro-pulse and continuous laser modes enable the surgeon to delineate the best laser application for the individual surgical patient. The animal OCT and histopathology studies confirm the precision of burn application and suggest that retinal/choroidal targeting is a function of energy transfer that is modulated best by pulse duration and power application. Ideally the PUREPOINT® 532 nm photocoagulator enhances the surgeon's interface to laser delivery through a combination of unique features that include a multi-function foot pedal, voice confirmation, RFID interface and integrated pre-population of laser settings, along with dual laser attachment ports. This laser system continues to move toward the ideal surgical paradigm that maintains control of key systems under the direct focus of the surgeon. RP

PUREPOINT® 532 nm Laser
Key features include:
• Voice Confirmation Technology
• Multi-Function Foot Pedal
• ENGAUGE® RFID Technology
• Dual Laser Attachment Ports

Advantages:
• Enhanced access to retinal periphery
• Defined laser delivery

The multifunctional foot pedal shifts control from the circulating nurse to the surgeon.

Two switched laser ports enable the system to be set up for both endophotocoagulation and laser indirect ophthalmoscopy.



Retinal Physician, Volume: , Issue: February 2009, page(s):