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Abstract
Ophthalmology was the first medical specialty to adopt lasers right after their invention more than 50 years ago, and they gradually revolutionized ocular imaging, diagnostics, therapy, and surgery. Challenging precision, safety, and selectivity requirements for ocular therapeutic and surgical procedures keep advancing the laser technologies, which in turn continue enabling novel applications for the preservation and restoration of sight. Modern lasers can provide single-cell-layer selectivity in therapy, submicrometer precision in three-dimensional image-guided surgery, and nondamaging retinal therapy under optoacoustic temperature control. This article reviews the evolution of laser technologies; progress in understanding of the laser-tissue interactions; and concepts, misconceptions, and accidental discoveries that led to modern therapeutic and surgical applications of lasers in ophthalmology. It begins with a brief historical overview, followed by a description of the laser-tissue interactions and corresponding ophthalmic applications.
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Affiliation(s)
- Daniel Palanker
- Department of Ophthalmology and Hansen Experimental Physics Laboratory, Stanford University, Stanford, California 94305;
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Wang J, Schuele G, Palanker D. Finesse of transparent tissue cutting by ultrafast lasers at various wavelengths. JOURNAL OF BIOMEDICAL OPTICS 2015; 20:125004. [PMID: 26720869 DOI: 10.1117/1.jbo.20.12.125004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 11/19/2015] [Indexed: 05/05/2023]
Abstract
Transparent ocular tissues, such as the cornea and crystalline lens, can be ablated or dissected using short-pulse lasers. In refractive and cataract surgeries, the cornea, lens, and lens capsule can be cut by producing dielectric breakdown in the focus of a near-infrared (IR) femtosecond laser, which results in explosive vaporization of the interstitial water, causing mechanical rupture of the surrounding tissue. Here, we compare the texture of edges of lens capsule cut by femtosecond lasers with IR and ultraviolet (UV) wavelengths and explore differences in interactions of these lasers with biological molecules. Scanning electron microscopy indicates that a 400-nm laser is capable of producing very smooth cut edges compared to 800 or 1030 nm at a similar focusing angle. Using gel electrophoresis and liquid chromatography/mass spectrometry, we observe laser-induced nonlinear breakdown of proteins and polypeptides by 400-nm femtosecond pulses above and below the dielectric breakdown threshold. On the other hand, 800-nm femtosecond lasers do not produce significant dissociation even above the threshold of dielectric breakdown. However, despite this additional interaction of UV femtosecond laser with proteins, we determine that efficient cutting requires plasma-mediated bubble formation and that remarkably smooth edges are the result of reduced thresholds and smaller focal volume.
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Affiliation(s)
- Jenny Wang
- Stanford University, Department of Applied Physics, 452 Lomita Mall, Stanford, California 94305, United States
| | - Georg Schuele
- Abbott Medical Optics, 1310 Moffett Park Drive, Sunnyvale, California 94089, United States
| | - Daniel Palanker
- Stanford University, Department of Ophthalmology, 452 Lomita Mall, Stanford, California 94305, United StatesdStanford University, Hansen Experimental Physics Laboratory, 452 Lomita Mall, Stanford, California 94305, United States
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Suhm N, Götz MH, Fischer JP, Loesel F, Schlegel W, Sturm V, Bille J, Schröder R. Ablation of neural tissue by short-pulsed lasers--a technical report. Acta Neurochir (Wien) 1996; 138:346-9. [PMID: 8861705 DOI: 10.1007/bf01411747] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The basis for most laser applications in neurosurgery is the conversion of laser light into heat when the incident laser beam is absorbed by the tissue. Irradiation of neural tissue with laser light therefore leads to its thermal damage. However, due to the diffusion of heat energy into the surrounding tissue, often there is thermal damage to neural tissue outside the area of the target volume. These are the characteristics of thermal laser/tissue interaction. In this paper we discuss how we used three different short-pulsed lasers to achieve non-thermal ablation of neural tissue. Three different short-pulsed lasers were used to generate ultrashort laser pulses in the picosecond to femtosecond range. The interaction of such laser pulses with tissue was predicted to be nonthermal. The short-pulsed lasers were used for the ablation of neural tissue using an in vitro calf brain model. The histopathological examination of the lesions revealed that the neural tissue had been removed very precisely without any sign of thermal damage to the surrounding tissue.
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Affiliation(s)
- N Suhm
- Abteilung Medizinische Physik, Deutsches Krebsforschungszentrum, Heidelberg, Federal Republic of Germany
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Oraevsky AA, Jacques SL, Esenaliev RO, Tittel FK. Pulsed laser ablation of soft tissues, gels, and aqueous solutions at temperatures below 100 degrees C. Lasers Surg Med 1996; 18:231-40. [PMID: 8778517 DOI: 10.1002/(sici)1096-9101(1996)18:3<231::aid-lsm3>3.0.co;2-t] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
BACKGROUND AND OBJECTIVE It is desirable for laser microsurgical procedures to remove tissue accurately and with minimal thermal and mechanical damage to adjacent non-irradiated tissues. Pulsed laser ablation can potentially remove biological tissue with microprecision if appropriate irradiation conditions are applied. The major goal of this study was to determine whether laser ablation is possible at temperatures below 100 degrees C. Another aim was to test thermoelastic and recoil stress magnitudes and to estimate their effects on phantom and biological tissue. STUDY DESIGN/MATERIALS AND METHODS Pulsed laser ablation of water (aqueous solution of potassium chromate) and water containing soft tissues (collagen gel and pig liver) irradiated under confined stress conditions was studied. The ablation mechanism and stages of the ablation process were determined based on time-resolved measurements of laser-induced acoustic waves with simultaneous imaging of the ablation process by laser-flash photography. RESULTS This study reveals the important role of tensile thermoelastic stress, which produces efficient cavitation that drives material ejection at temperatures substantially below 100 degrees C. Ablation thresholds for the aqueous solution, collagen gel, and liver were 20, 38, and 55 J/cm3, respectively, which correspond to temperature jumps of 5, 10, and 15 degrees C. Two distinct stages of material ejection were observed: (1) initial removal of small volumes of material due to the rupture of single subsurface bubbles, (2) bulk material ablation in the form of jets produced by intense hydrodynamic motions formed upon collapse of large bubbles after coalescence of smaller bubbles. The duration of material ejection upon short-pulse ablation may vary from microseconds to submilliseconds, and depended on the mechanical properties of materials and the incident laser fluence. CONCLUSION Nanosecond laser ablation of water, gels, and soft tissue under confined-stress conditions of irradiation may occur at temperatures below 100 degrees C. This ablation regime minimizes thermal injury to adjacent tissues and involves thermoelastic stress and recoil pressure magnitudes, which may be tolerated by tissues adjacent to an ablated crater.
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Affiliation(s)
- A A Oraevsky
- Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77251-1892, USA
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Fischer R, Hibst R, Schröder D, Puhl W, Steiner R. Thermal side effects of fiber-guided XeCl excimer laser drilling of cartilage. Lasers Surg Med 1994; 14:278-86. [PMID: 8208054 DOI: 10.1002/lsm.1900140310] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We examined thermal effects during ablation of human joint cartilage using two XeCl excimer lasers with pulse durations of approximately 20 ns and 60 ns. An increase in radiant exposure or repetition rate caused a rise in tissue temperature up to 82 degrees C at a 100-microns distance. With increasing distance from the crater edge, the temperature dropped exponentially. Radiant exposures higher than 1.8 J/cm2 and repetition rates above 20 Hz lead to a formation of hot gaseous products escaping from the laser crater. When osteoarthritic cartilage is irradiated, these gases spread inside the tissue causing a temperature rise of > 50 degrees C at a distance of 1 mm from the crater edge. In the contact mode, we found a linear rise of ablation rate with increasing repetition rate both in air or saline. But ablation rates in saline were only half the rates achieved in air. Both phenomenons can be explained by additional thermal effects of excimer lasers working in the range of higher repetition rates and pulse energies.
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Affiliation(s)
- R Fischer
- Orthopädische Klinik und Querschnittgelähmtenzentrum, Universität Ulm, Germany
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Esenaliev RO, Oraevsky AA, Letokhov VS, Karabutov AA, Malinsky TV. Studies of acoustical and shock waves in the pulsed laser ablation of biotissue. Lasers Surg Med Suppl 1993; 13:470-84. [PMID: 8366748 DOI: 10.1002/lsm.1900130412] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Quantitative studies are conducted into the absolute pressure values of the acoustical and shock waves generated and propagating in a biotissue under pulsed (tau p = 50 ns) UV (lambda = 308 nm) laser irradiation (below and above the ablation threshold). Powerful (several hundreds of bars in pressure) high-frequency (f approximately 10(7) Hz) acoustic compression and rarefaction pulses are found to be generated in the biotissue. The amplitudes and profiles of the acoustic pulses developing in atherosclerotic human aorta tissues and an aqueous CuCl2 solution under laser irradiation are investigated as a function of the laser pulse energy fluence. The results obtained point to the absence of the cold spallation of the objects of study by rarefaction waves. Based on experimental data, the rise rates, pressure gradients, and propagation velocities of shock waves in the biotissue are calculated. The experimental data are found to agree well with the theoretical estimates.
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Affiliation(s)
- R O Esenaliev
- Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow Region
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Mayer HM, Müller G, Schwetlick G. Lasers in percutaneous disc surgery. Beneficial technology or gimmick? ACTA ORTHOPAEDICA SCANDINAVICA. SUPPLEMENTUM 1993; 251:38-44. [PMID: 8451982 DOI: 10.3109/17453679309160113] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- H M Mayer
- Department of Orthopedic Surgery, Free University of Berlin, Germany
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Hanke H, Haase KK, Hanke S, Oberhoff M, Hassenstein S, Betz E, Karsch KR. Morphological changes and smooth muscle cell proliferation after experimental excimer laser treatment. Circulation 1991; 83:1380-9. [PMID: 2013155 DOI: 10.1161/01.cir.83.4.1380] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
BACKGROUND Little is known about the mechanism(s) in the development of restenosis after excimer laser angioplasty. Thus, the rationale of this study was to determine the time course of intimal and medial smooth muscle cell (SMC) proliferation and histomorphological changes after experimental excimer laser treatment. METHODS AND RESULTS Laser ablation was performed in the right carotid artery of 34 New Zealand White rabbits after development of a fibromuscular plaque by repeated weak electrical stimulations. The vessels were excised 3, 7, 14, 21, 28, and 42 days after excimer laser treatment. Staining of alpha-actin was used to identify SMCs. In five rabbits (15%), a stenosis of more than 50% of luminal area was due to intimal proliferation of SMCs, and in four other rabbits, a total occlusion was due to organized thrombi. After the initial ablation of the performed plaque (13 +/- 6 intimal SMC layers) a continuous increase of intimal wall thickness was found from 7 +/- 6 SMC layers at 7 days to 28 +/- 5 intimal SMC layers at 28 days after excimer laser ablation (p less than 0.01). After 42 days, no additional increase of intimal thickening occurred. After bromodeoxyuridine labeling, the extent of cell proliferation (percent of cells undergoing DNA synthesis) in the intima and media was determined using a monoclonal antibody against bromodeoxyuridine. Immunohistological quantification of SMC proliferation in the intima revealed a significant increase of cells undergoing DNA synthesis at 3 (p less than 0.05) and 14 (p less than 0.01) days after laser treatment. Medial proliferation of SMCs was delayed and had a significant increase 7 days (p less than 0.05) after intervention. Twenty-one days after laser treatment, SMC proliferation in the intima as well as in the media was normalized. CONCLUSIONS The proliferative response of SMCs after experimental excimer laser treatment will occur as a dynamic process with a maximum of SMCs undergoing DNA synthesis during 14 days after laser ablation, resulting in an increase of intimal thickening within 4 weeks after laser treatment. The extent of intimal hyperplasia due to SMC proliferation after excimer laser treatment is comparable with the effect of transluminal balloon angioplasty in this experimental model.
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Affiliation(s)
- H Hanke
- Department of Medicine, University of Tübingen, FRG
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Percutaneous peripheral laser angioplasty with a pulsed Nd-YAG laser and sapphire tips. Lasers Med Sci 1991. [DOI: 10.1007/bf02042645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Affiliation(s)
- A L McKenzie
- Radiotherapy Physics Unit, Bristol Radiotherapy and Oncology Centre, UK
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Affiliation(s)
- J M Isner
- Department of Medicine (Cardiology), St. Elizabeth's Hospital, Tufts University School of Medicine, Boston, MA 02135
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Steg PG, Rongione AJ, Gal D, DeJesus ST, Clarke RH, Isner JM. Pulsed ultraviolet laser irradiation produces endothelium-independent relaxation of vascular smooth muscle. Circulation 1989; 80:189-97. [PMID: 2736751 DOI: 10.1161/01.cir.80.1.189] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Recent studies have shown that continuous wave laser irradiation induces contraction of vascular smooth muscle, except at powers far below the threshold for tissue ablation. To determine the corresponding effects of pulsed laser irradiation on vascular smooth muscle tone, vascular rings of rabbit thoracic aorta were mounted isometrically with 1 g tension in Krebs-bicarbonate buffer and irradiated with 308 or 351 nm from an excimer laser through a 400-microns optical fiber. A total of 250 exposures were performed with 1-6.5 mJ/pulse (fluence = 0.8-5.5 J/cm2), 10-50 Hz, and cumulative exposures of 10-120 seconds. Excimer laser irradiation in combinations of pulse energy (PE), repetition rate (RR), and cumulative exposure below, at, or above threshold for tissue ablation consistently produced relaxation unassociated with contraction in each of the 250 exposures. For the total 250 exposures, the magnitude of relaxation (reduction in recorded tension, Rmax) was 55 +/- 4% (mean +/- SEM) of maximum vasomotor reactivity recorded in the specimen in response to administration of serotonin. Rmax varied directly with both PE and RR. When PE was increased from 1 to 5 mJ/pulse (n = 13), Rmax increased from 57 +/- 19% to 80 +/- 19% (p less than 0.0001); when RR was increased from 10 to 50 Hz (n = 10), Rmax increased from 27 +/- 8 to 46 +/- 8 (p less than 0.0001). Rmax varied independently of endothelial integrity (assessed anatomically and pharmacologically) and wavelength (308 vs. 351 nm). Simultaneously recorded tissue-temperature profiles disclosed that during pulsed laser irradiation, tissue temperature rise did not exceed 5 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- P G Steg
- Department of Medicine, St. Elizabeth's Hospital, Tufts University School of Medicine, Boston, Massachusetts 02135
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Kaufmann R, Hibst R. Pulsed Er:YAG- and 308 nm UV-excimer laser: an in vitro and in vivo study of skin-ablative effects. Lasers Surg Med 1989; 9:132-40. [PMID: 2716457 DOI: 10.1002/lsm.1900090208] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Using a pulsed XeCl excimer laser (308 nm) and a pulsed Er:YAG laser (2,940 nm), we investigated skin ablation as a function of pulse number, radiant energy, and repetition rate. In vitro analysis of lesions performed in freshly excised human skin were consistent with in vivo results obtained from experiments on pig skin. Pulsed 308 nm laser radiation caused considerable nonspecific thermal tissue injury followed by an inflammatory reaction and impaired healing of lesions in vivo. These findings were especially pronounced with higher repetition rates, which would be required for efficient destruction of larger lesions. On the other hand, the 2.94 microns Er:YAG laser radiation produced clean and precise lesions with only minimal adjacent injury. In vivo skin ablation caused intraoperative bleeding with deeper penetration. The Er:YAG laser offers a promising surgical tool for careful removal of superficial epidermal lesions, if higher repetition rates, and an appropriate laser beam delivery system are available for clinical use.
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Affiliation(s)
- R Kaufmann
- Institut für Lasertechnologien in der Medizin an der Universität Ulm, Federal Republic of Germany
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McKenzie AL. An extension of the three-zone model to predict depth of tissue damage beneath Er:YAG and Ho:YAG laser excisions. Phys Med Biol 1989; 34:107-14. [PMID: 2928374 DOI: 10.1088/0031-9155/34/1/011] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Pulsed lasers such as Er:YAG and Ho:YAG with outputs at mid-infrared wavelengths emit radiation which may be transmitted by fibre to a treatment site. The thickness of soft-tissue damage beneath excisions made by these lasers is predicted using an extension to a model previously devised for CO2 laser radiation. The minimum achievable thickness occurs at a water absorption peak and at such high irradiance that heat cannot diffuse significantly compared with the radiation penetration depth. This minimum thickness is estimated to be in the order of 10 microns for the Er:YAG laser.
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Affiliation(s)
- A L McKenzie
- Northern Regional Medical Physics Department, Newcastle General Hospital, UK
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Affiliation(s)
- J S Forrester
- Cedars-Sinai, Medical Center, Los Angeles, CA 90048-0750
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FORRESTER JAMESS, LITVACK FRANK, GRUNDFEST WARREN, MOHR FRIEDRICHW, PAPAIOANNOU THANASSIS, GOLDENBERG TSVI, LAUNDENSLAGER JAMES. The Excimer Laser: Current Knowledge and Future Prospects. J Interv Cardiol 1988. [DOI: 10.1111/j.1540-8183.1988.tb00391.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Wollenek G, Laufer G, Grabenwöger F. Percutaneous transluminal excimer laser angioplasty in total peripheral artery occlusion in man. Lasers Surg Med 1988; 8:464-8. [PMID: 2976444 DOI: 10.1002/lsm.1900080504] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Laser angioplasty and laser-assisted angioplasty have become a clinical reality. Producing sharply defined borders of the ablated area with minimal adjacent thermal damage, excimer lasers offer several proven and some potential advantages over conventional systems. To evaluate the feasibility of excimer laser angioplasty, we have treated one patient using 308-nm radiation via a bare fiber in direct contact with the total occlusion of a right femoral artery. The lesion was successfully recanalized, thus allowing easy passage of the balloon catheter and subsequent dilatation. This percutaneous laser recanalization of an occluded peripheral artery is one of the first to be done in man using excimer laser radiation, thus demonstrating that the technique is feasible and the system is potentially useful.
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Affiliation(s)
- G Wollenek
- Second Surgical Department, University of Vienna, Austria
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