Review Articles

Lasers: Principles and Surgical Applications Kayvan Shokrollahi1, Elizabeth Raymond2 and M.S.C. Murison1 1 Dept of Plastic and Reconstructive Surgery, Morriston Hospital, Swansea 2 The Training and Education Centre, 395 Mansfield Rd, Nottingham, NG5 2DL, UK Correspondence to: Mr Kayvan Shokrollahi, Dept. of Plastic and Reconstructive Surgery, Morriston Hospital, Morriston, Swansea, SA6 6NL, United Kingdom.

Introduction move freely to a higher, but less stable energy level. Because the In 1917 Albert Einstein put forward a theory of “stimulated atom is unstable in this state, the returns to a lower level emission” - that could “stimulate” the emission of almost immediately and it doing so spontaneously emits a tiny another that would possess identical properties to the first1. packet of energy in the form of a photon8 (figure 1): This is the idea behind laser light and in 1958 Townes and Schawlow2 worked on this theory to establish the principle that led to the development of the Laser: Light Amplification by Stimulated Emission of Radiation. In 1960 Theodore Maiman demonstrated the first practical laser with a crystal of ruby stimulated by a flashlamp and to amplify the lasing action3. The beam was a deep red colour with a wavelength of 694 nm. Since that first laser, many more materials have been Figure 1: As are excited, they move to a discovered that are capable of producing laser light including higher energy level and release photons as they return to their dyes, gas mixtures and semiconductor materials, many of which resting or “ground” state. are described below and presented in table 1. If the emitted photon is close to another atom with electrons also It has taken decades to develop reliable, appropriately designed in the excited state, it will trigger that atom to release its higher laser systems for routine use in medical and other applications4. level photon and emit a further photon of laser light. This is More recently, Intense Pulsed Light (IPL) systems are being used stimulated emission (figure 2). for many similar applications as lasers5.

Laser Physics White light from a light bulb is not ‘white-coloured’- light. It is made up of many different colours or wavelengths of the electromagnetic spectrum (EMS), and what we see is the visible part of this spectrum6. These electromagnetic energies come in all forms including sunlight, microwaves, radio waves and of course, “light”. Some parts of the “optical” region of the EMS, such as ultraviolet (UV) and (IR) light, are not visible to human eyes, and all of these wavelengths (colours) or frequencies of light combine to make what we perceive as white light7. The electromagnetic spectrum is included as part of figure 4 later on.

Laser light differs from “ordinary” light in a number of ways. The light comprises only one colour, due to the emission of an xtremely narrow range of wavelengths of light - typically described as monochromatic4. Unlike most conventional light sources, which spread light in all directions, laser light is collimated, which means that the light travels in a narrow beam with all waves in parallel, without significant Figure 2: An illustration of the lasing process. divergence4. This feature is essential for minimising loss of power through beam delivery systems such as fibre optics or articulated These two photons of identical energy and frequency then travel arms. The most significant feature of laser light is the property of together in perfect step or “phase” - a unique feature of coherent 9 coherence7. This means that the waves are highly ordered in space light . The light energy is amplified by photons colliding with and correlated in time resulting in an additive effect upon the other excited atoms and simultaneously releasing yet more pho- amplitude or power. Furthermore, a coherent source can be tons. However, this process will only continue if there are more focused to a far smaller spot size than an incoherent source. This atoms in the excited state than the lower states and in order to allows creation of extremely high power density in an area small achieve this condition, the lasing medium containing the atoms 8 enough to cause tissue damage4. must be kept “excited” by the energy source . The laser light is reflected back and forth inside the laser by a pair of mirrors as The Process of Lasing illustrated in figure 2. When there is sufficient laser light inside the cavity, a shutter can be opened to release the light in the form The creation of laser light begins when electrons of a lasing of a laser beam. This beam will be monochromatic, coherent and medium are made to change energy levels by an excitation source usually of very low divergence. Table 1 groups the four major such as a flashlamp, electric current or another laser8. If the input types of active media for common medical , and shows their energy is of the appropriate level, the electrons will absorb and laser wavelengths.

28 The Journal of Surgery • Volume 2 • Issue 1 • 2004 Fluence pulse duration, it is possible to cause selective destruction of A laser beam will contain an amount of power or energy that is a given target by laser light. This is termed selective delivered in a beam of a fixed or variable area. Fluence is one of photothermolysis13. Each target has its own characteristics for the most important and critical aspects of laser treatment and is absorbing particular wavelengths of light8 (figure 3): a measure of energy per unit area4. Most medical laser systems use cm2 as the area for spot size, so the power or energy “density” is quoted in Watts (W) cm2 or Joules (J) cm2. For a given amount of power or energy, a larger spot size will spread the beam over a greater area, thus decreasing the thermal impact of the beam. Conversely, a smaller spot size will “concentrate” the power, thus delivering more power or energy into the area. If any one of these variables changes the effect upon tissue will also change.

Delivery systems The beam delivery system is the device or attachment that transmits the laser beam to the treatment site. The laser wavelength and beam energy dictate the type of beam delivery system that can be used, due to the transmission or absorption characteristics of optical elements7. For example CO laser 2 Figure 3: Comparative absorption spectra for oxyhaemoglobin wavelengths cannot be transmitted by fibre-optics, due to (Hb), melanin and water alongside the electromagnetic spectrum, absorption rather than transmission by the quartz fibre8. showing common laser wavelengths and their depth of skin Laser wavelengths that can be transmitted by conventional quartz penetration. fibre optics and wavelengths transmitted are restricted (approximately from 300 nm to 2.5 m)10. Q-switching is a method • Oxyhaemoglobin in blood absorbs light primarily in the of producing massive increases in peak power through delivering ultraviolet, green and yellow regions of the spectrum, and the laser energy over nano-second pulse durations. allows the targeting of blood vessels by lasers. This allows for targeted tissue destruction, but precludes • Melanin absorbs light across the ultraviolet and visible fibre-optic delivery due to the very high-energy transmission. regions, well into the infrared range. A therapeutic window The alternative to fibre-optics is delivery via an articulated arm. exists between 630 and 1100nm where melanin absorption Most arms consist of two matched sets of rotating mounts, exceeds that of haemoglobin and penetration is deep. one long tube, one short tube, a launch plate and a counterbalance • Water and collagen, which absorb light significantly in the or spring assist. The articulated arm can transmit both an invisible infrared region. treatment beam (e.g. CO2 or Nd:YAG) and a visible aiming beam (e.g. HeNe or diode). Care should be taken to avoid knocking Blood vessels as a target articulated arms as the two beams can become misaligned relative When targeting blood vessels with laser light, the true target to each other, causing obvious loss of precision. is haemoglobin. The aim of laser treatment is to heat the blood in The laser may be delivered to the target either as a continuous the vessel sufficiently to cause a thermal injury to the blood vessel collimated beam (continuous wave, CW) until the laser foot pedal wall and the lowest temperature that must be achieved to produce is released, or as a burst of variable speed outputs (pulsed wave, this effect is 70oC15,16. The consequences are an inflammatory PW), which fire at a desired frequency. A pulsed output delivers reaction with re-absorption of the damaged vessel walls and, the light energy in a very short space of time which has a ideally, replacement with vessels of normal caliber already17. mechanical disruptive effect (photo-disruption), such as with a pulsed or Q-switched laser. The continuous beam is Blood vessels vary considerably in size from 20 to 30 microns useful during cutting or ablative applications11. (?m) in the papillary dermis of normal skin, to 500m or more in mature port wine stains (PWS) and some telangiectasia. Laser and tissue interactions The typical range of vessel diameter in PWS is between 50 and When laser light is delivered to tissue, or any surface, a number of 300m. When considering selective wavelengths for blood specific interactions can occur. If a laser beam can be transmitted vessels, the wavelength maximally absorbed by haemoglobin and through a material there will be little or no absorption and minimally absorbed by the other major competing pigment therefore little or no thermal effect. The depth of transmission into is optimal. However, another consideration is the depth of the t tissue depends upon tissue type, laser wavelength and laser arget blood vessels. If deeper penetration is required, 12 fluence . For example, an ND:YAG laser beam can be transmitted longer wavelengths may be preferred because of their reduced through quartz elements such as a fibre optic, but a CO2 laser dermal scattering which increases depth of penetration18. beam will not. Melanin and other pigments A laser beam that is not transmitted through a material is absorbed, Most of the lasers now available for treating pigmented lesions and as the tissue or material absorbs the laser beam, heat energy is and tattoos (Q-switched ruby, Q-switched Nd:YAG and dye lasers) 13 produced which can cause thermal damage to the tissue . deliver high energy and very short pulses. The result is a Selective absorption is the key to the majority of laser/light predominantly photomechanical disruption of the target without treatments, which “target” a particular wavelength to a particular necessarily fully denaturing it11. This laser-target interaction relies site, e.g. haemoglobin in blood vessels. By choosing a wavelength in part on disruption of the cell that contains the pigment, of light that is preferentially absorbed by one component of tissue, and subsequent repair mechanisms. When the aim is to destroy it is possible to target that structure and leave surrounding tissues larger melanin-containing structures (e.g. hair follicles19 and nests relatively unaffected. If the rate of energy absorption is slow, of melanocytes in some congenital naevi20,21), a longer pulse thermal energy is produced. However, if the rate is fast, shock duration (typically termed “normal” mode or long pulsed) is waves are produced which can cause explosive mechanical required. This allows heat to diffuse away from the melanin to 14 disruption . When thermal energy is produced, as the length of damage non-melanin-containing parts of the structure. In these exposure of the target structure to the laser light increases, more circumstances, thermal damage and mechanical factors are both of the heat produced diffuses into the surrounding tissue. involved in the process. Therefore, by selecting an appropriate wavelength, fluence and

The Journal of Surgery • Volume 2 • Issue 1 • 2004 29 The wavelength suitable for treating melanin-pigmented lesions can be any- where along the visible or near infrared portion of the electromagnetic spectrum because melanin absorbs light right across these wavelengths (which is why melanin is black in colour) figure 3. However, deeper penetration of light occurs in the red and near infrared portions (>600 nm) rather than with shorter wavelengths (532nm for example)22. In the case of melanin pigmentation at the single cell or sub-cellular level, the major mechanism is probably the destruction of melanocytes23 and other melanin-containing cells such as keratinocytes24. This is followed by repair mechanisms, which include re-population of the treated area with melanocytes and re-melanisation of these cells23. The response to treatment is largely dictated by these repair mechanisms. In the case of melanin pigmentation in larger structures (e.g. hair follicles) there is destruction both of melanocytes and adjacent non-melanin Figure 4: Treatment of Rhinophyma with a carbon containing cells. The clinical results are less reliable in these dioxide laser. circumstances and depend on the number and distribution of melanin- containing cells within the target structure23. Surface cooling In circumstances where an intended laser target is in the dermis, In the case of tattoo pigment, a combination of mechanisms is absorption by melanin in the epidermis (and subsequent epidermal probably involved in removing the ink particles. Firstly, the tattoo or superficial dermal damage) can be a significant problem and pigment is altered by a thermo-chemical reaction11. Secondly, will limit the effectiveness of laser treatment37. This is particularly fragmentation of the pigment alters its optical properties25. Thirdly, true where there is significant skin pigmentation, and where high there is trans-epidermal or macrophage mediated elimination of fluence is necessary to produce useful effects. Methods that cool altered pigment25,26. Finally, there may be laser-induced changes the epidermis but not the dermis can improve treatment efficacy in the optical properties of the skin overlying the pigment24. and reduce adverse effects38.

Water as a target: non-specific destruction With dynamic cooling, a spray of a volatile liquid (often tetraflu- In some circumstances, lasers can be used to cause non-specific oroethane) is delivered to the skin surface over 10 to 100 destruction, and in skin, this can be confined spatially to a lesion milliseconds. This leaves a thin layer that evaporates within a few with sparing of surrounding tissues - the principle of selective milliseconds resulting in significant pre-cooling of the skin photothermolysis13. The benefits of this approach are reduced post- surface (figure 5)38,39. treatment inflammatory reaction, faster healing and less scarring27 than with other destructive methods, such as cryotherapy An alternative method is contact cooling40, which can be achieved or cautery. One example of this approach is the use of the 1064 by a number of means including damp swabs, ice packs, cool nm Nd:YAG laser in long pulse mode (pulse duration 0.5s). water, cool aqueous gel, cold air or cooled sapphire windows. The infra-red (IR) beam from this laser is primarily absorbed by Devices for contact cooling rarely reduce temperatures to those water in the tissues, whilst the longer pulse duration causes seen with dynamic cooling, and by their nature need to be applied non-specific diffusion of heat and this thermal effect can penetrate for at least a few seconds prior to laser impact. As a result, approximately 4 mm into the skin12. This modality can be used to relatively greater cooling occurs deeper in the skin layers coagulate deep vascular lesions that are beyond the usual range than with dynamic cooling. Contact cooling is therefore more (approximately 1.2mm) of more selective wavelengths. This laser applicable where targets are more deeply situated, such as hair is also useful for palliative surgical therapy, for example in follicles or deep vascular lesions, or where a longer pulse duration recanalisation of obstructions in the airways or oesophagus with (which causes greater thermal diffusion) is used41 (figure 5): minimal bleeding28,29.

The CO2 laser, which emits light in the far IR (10,600 nm) and has tissue water as its major target, can also vaporise tissue, leaving only a very narrow zone of thermal tissue damage30. This laser has particular advantages for skin lesions that cover large areas (e.g. epidermal naevi, resurfacing of photo-aged skin). Healing predominantly occurs from the wound base, rather than from the wound edges, after the CO2 laser vaporises a layer of skin leaving a layer of desiccated tissue and a zone of thermal coagulation30-32, giving a relatively bloodless operative field and Figure 5: Contact (left) and dynamic cooling (right). Contact good visibility. A long list of conditions have been successfully cooling has a deeper effect than dynamic treated using , including neurofibromas33 cooling and is more suited to deeper targets in the skin. As the and rhinophyma34 (figure 4), cosmetic skin resurfacing35, duration of cooling is short, dynamic cooling is more appropriate neurosurgery36 and many others. for lasers with shorter pulse duration.

30 The Journal of Surgery • Volume 2 • Issue 1 • 2004 Common Medical Lasers Active Medium Laser Type Wavelength / Colour The Nd:YAG Laser (1064 nm fundamental) The neodymium laser is the most common of the solid state lasers. Gas: molecules in a Argon 488 nm Blue The active medium in an Nd:YAG laser is a crystal rod of yttrium gas-active medium are 514 nm Green aluminium garnet (YAG) with the impurity Neodymium (Nd). excited by an electric Its main advantage is its thermal stability which allows current - either pulsed Neon (HeNe) 632 nm Red or continuous an Nd:YAG laser to produce a good quality, continuous beam at room temperature. The fundamental Nd:YAG laser wavelength is (CO2) 10.6 µm Mid IR in the near IR at 1064nm. Since this wavelength is invisible, an aiming beam is often required. This is a versatile laser, and is 19, 42 Excimer ArF 193 nm UV particularly useful in long pulsed mode for hair removal , due to KrCl 222 nm depth of penetration, in addition to removal of tattoos and KrF 248 nm pigmented lesions if Q-switched43. XeCl 308 nm XeF 351 nm Frequency doubled Nd:YAG (532 nm) (KTP laser) This is essentially a variation upon an Nd:YAG laser and uses a Krypton Kr 531 nm Green crystal to shorten (effectively half) the 1064nm fundamental 568 nm Yellow Nd:YAG wavelength to 532nm. The crystal is usually 647 nm Red potassium titanyl phosphate and hence the name KTP laser. Since the 1064nm wavelength is halved, its frequency doubles Helium Cadmium 325 nm UV and therefore the emergent beam is visible at 532nm. (HeCd) The green beam at 532nm is strongly absorbed by haemoglobin, 44 (metal vapour laser) melanin and other similar pigments . Fibre optics, clear fluids, and structures such as the lens of the eye transmit this wavelength. Some Nd:YAG lasers combine the fundamental wavelength with a Gold vapour 627 mn Red (metal vapour laser) KTP in a single unit with the added function of a Q-switch, offering great flexibility of applications and treatment. An example of treatment for telangectasia and keloid is Neodymium Yttrium Solid State: lasers use 1064 nm Near IR illustrated in figure 6, and treatment of PWS is shown in figure 7: a crystal as the active Aluminium Garnet medium. Typically an (Nd:YAG) optically clear type of material composed of a Frequency doubled 532 nm Green host crystal, laced with an YAG (KTP) impurity called a dopant. The dopant produces the laser energy typically Ruby 694 nm Deep red excited by a flashlamp or diode laser. Erbium YAG (Er:YAG) 2900 nm Near IR

Holmium YAG 2100 nm Near IR (Ho:YAG) Figure 6: Telangectasia (left of each picture) and keloid scars (lower right of each picture) over the chest wall and axilla after Nd Yttrium Lithium 1047 nm Near IR Tuneable solid state mastectomy with radiotherapy - results after five treatments with a fluoride (Nd:YLF) long pulsed KTP laser showing telangectatic areas to be much improved when compared to the untreated (by patient request) Alexandrite 720 800 nm Near IR axillary patch. The keloid scars were also treated, and are much (Cr:BeAl O ) 2 4 Typically 760 nm less prominent and erythematous as a result.

Ti:Sapphire 670 - 1100 nm

(Ti:Al2O4)

Liquid: a flowing organic Tuneable dye 400 - 1000 nm Various dye that when excited by laser Wavelength another laser beam depends on dye, eg. produces a wide range of Rhodamine 6G 550 - wavelengths.Often require 650 nm. more maintenance and can be less reliable.

Semiconductor/diode: 670 - 1551 nm layers of semiconductor Diodes, eg. GaAs, Near IR crystal material (eg. InGaAs, GaAs) form the active medium excited by a electric current. Small, compact and increasingly high powers.

Figure 7: Result of treatment of a Port Wine Stain after 7 Table 1. Active media for common medical laser types. treatments with a frequency doubled Nd:YAG laser (KTP laser).

The Journal of Surgery • Volume 2 • Issue 1 • 2004 31 Alexandrite Lasers (720 - 800nm) The (UV outputs) The Alexandrite laser is a tuneable solid state laser that can emit The excimer laser gets its name from excited dimer which refers wavelengths between 701 and 826nm, although most systems to a molecule that is relatively stable when excited. Excimer lasers operate at 755nm. The laser is similar in construction to an use compounds of rare gases and halogens such as; argon fluoride Nd:YAG laser, can be fibre-optically delivered unless Q-switched, (193 nm), krypton fluoride (248nm), xenon chloride (308nm) and and operates in continuous (CW) and pulsed (PW) modes. One xenon fluoride (351nm). Excimer beams are pulsed, high energy advantage of an Alexandrite laser for hair removal is the longer outputs. The UV wavelengths are absorbed by proteins, and on the wavelength than the ruby laser, giving deeper penetration into the surface of the cornea tissue penetration is less than 1µm49. skin. An example of tattoo removal with a Q-switched Alexandrite They are particularly useful in ophthalmic surgery. An example is laser is illustrated in figure 8: of the Lasik50 technique for correction of myopia is shown in figure 9:

Figure 9: Lasik Surgery for correction of myopia. The excimer beam alters the contour of the cornea beneath a thin corneal flap. Figure 8: Tattoo removal with a Q-switched alexandrite Laser. Dye Lasers (400 - 1000 nm) One drawback of many lasers is the emission of only one Ruby Lasers (694 nm) wavelength. The dye laser has the advantage of being “tunable” The ruby laser is very similar to a pulsed Nd:YAG but emits a red over a range of wavelengths. A liquid, organic dye dissolved in beam of 694nm. Ruby lasers are excited by flashlamps and can be water or solvent is exposed to an intense light source, typically a Q-switched to produce a high peak power pulsed output (as used flashlamp. The dye absorbs the light of one wavelength, fluoresces for tattoo removal). Ruby lasers were the first to be used for and emits light over a broad range of visible colours. A tuning tattoo removal because of good penetration into the skin and element in the laser cavity can cause a specific wavelength to lase. high absorption of this wavelength by dark blue and black Usually dye lasers operate from 400 to 1000 nm by changing the pigmentation4, 5. dye and other parameters. The dye in the laser will undergo photo-induced dye disintegration and so frequent changes of dye Argon (488, 514 nm) and Krypton Lasers (531+ nm) and solvents are necessary - with the attendant health hazards this Argon lasers produce two prominent wavelengths: 488 nm (blue) might pose8. Tunable dye lasers can emit continuous or pulsed and 514nm (green). The Argon gas is excited by an beams, the latter making them useful for removal of tattoos electrical current and emits a CW beam. Argon wavelengths are (figure 10) as well as other pigmented and vascular lesions for readily absorbed by haemoglobin, melanin and other similar which it is often the treatment of choice51 (figure 11). pigmentation, and have been used successfully in the treatment of PWS46. They are transmitted well by fibre optics and clear Diode Lasers (670 - 1551 nm) structures (such as in the eye), making the argon laser particularly Diode lasers have a diversity of applications in the useful for ophthalmic surgery11. medical field. Small and compact, they can be “stacked”to produce considerable output powers. The active material is a Carbon Dioxide (CO2 ) Lasers (10,600 nm) semi-conducting crystal, usually gallium arsenide (GaAs) or The CO2 laser continues to be a major instrument for laser similar compounds. A current passes through a “sandwich” of two surgery. A CO2 laser contains specific concentrations of CO2, types of lasers consisting of such compounds (called p-type and and helium gases which are excited by electrical currents. n-type substrates) to produce a beam in the near IR (0.8 - 1.5 ?m). The precise wavelength depends upon the material used in the CO2 lasers emit an invisible, far IR beam at 10,600 nm which is semiconductor layers. The beam from a diode laser is usually highly absorbed by water making it ideal for tissue removal47. more divergent than that of other lasers, requiring additional optics Many lasers such as ruby or argon rely on absorption by a to produce a collimated output beam. Beams can be CW or chromophore of specific colour to achieve an effect, and therefore pulsed. The advantage of diode systems is their compactness, will not be effective on tissues lacking such pigment. As the beam high efficiency and reliability. Some laser products use low power absorption of CO lasers is independent of tissue colour, 2 visible diode lasers in place of Helium-Neon (HeNe) lasers for non-pigmented or clear tissues will also absorb this wavelength aiming beams. A summary of these and other lasers, and their and can therefore be effectively targetted. However, because applications in surgery, is provided in table 2: this wavelength is readily absorbed by water it will not penetrate far into tissues (0.1 to 0.23 mm) without repeated or prolonged use - hence its use for superficial lesions and resurfacing of the skin48 (figure 6).

32 The Journal of Surgery • Volume 2 • Issue 1 • 2004 Intense Pulse Light Sources (IPL’s) Surgery in General - CO2 Nd:YAG, Ho:YAG IPL’s are a recent development. They are not lasers, but have • Haemostasis similar indications to many dermatalogical lasers, except that they • Sealing of lymphatics cannot produce the type of beam generated by a Q switched laser. • Cutting They are significantly cheaper than lasers. A number of IPL Urology - Pulsed dye, Ho:YAG, KTP, Diode systems are now available for hair removal treatments, often with • Stones: bladder or kidney claims of being safe and effective52,53. A high intensity flash lamp • Tumours of bladder and upper renal tract produces non-coherent “broad band” light from the UV to IR • Ureteric strictures region of the spectrum. This light is filtered to select just the wave- • Bladder neck incisions lengths needed for treatment, e.g. 515 to 1200nm. The filters can • Prostate coagulation be changed according to the skin and hair colour of the patient or • Prostate resection treatment modality e.g. for vascular treatments. IPL’s can also produce single, double and even triple pulses separated by a vari- Gynaecology - Nd:YAG, CO , Diode 2 able interpulse delay - a control not possible with many laser • External - condylomas systems. • Laparoscopic treatment • Hysteroscopic treatment The hand pieces typically have larger treatment areas than an • Foetoscopic treatment equivalent laser hand piece. This, combined with larger beam sizes • Colposcopic treatment and fast operation, is an advantage for treating large areas such as the back5. Clearance and success rates may be comparable with ENT - CO2, KTP, Nd:YAG, KTP, Diode • Microlaryngeal/vocal chords laser systems and the greater treatment variables may make it 5 • Respiratory papillomas possible to safely treat darker skin types . It is still important • Middle ear to protect the eyes against high power light sources, even those • Turbinates from non- laser sources. • Polyps • Sinus surgery Safety and Training Whilst laser and intense pulsed light technology offers many Gastroenterology - Nd:YAG, Diode advantages in surgical therapies, it should be clear that their • Recanalisation of oesophagus correct and safe use requires careful assessment and control of the • Gastric tumours • Actively bleeding ulcers given laser treatment and environment. • Liver disease Many hazards exist with laser use, including electrical, Orthopaedic Surgery - Nd:Yag, Ho:YAG mechanical, chemical, biological, optical and firehazards as well • Cutting & ablating soft/hard tissue as concerns with regards to toxic effects of laser plume54,55. Control • Smoothing cartilage measures should be implemented to minimise these hazards in • Knee surgery accordance with legislation and common sense, and protective • Lumbar disc decompression equipment that is available should be used and maintained appropriately. Oral & Maxillofacial Surgery - CO2 Nd:YAG • Tumour excision/biopsy Laser and intense pulsed light systems continue to advance • Vaporisation of papillomas rapidly in technology and applications. Serious consideration must be given to the correct selection, installation, training and use of Thoracics - Nd:YAG, CO2 the equipment. At all times the safety of the operator, as well as • Recanalisation of trachea those receiving treatment, must be ensured and those undertaking • Recanalisation of upper airways Ophthalmology - Nd:YAG, Krypton, argon, excimer treatments should be suitably trained in order to identify and • Diabetic retinopathy prescribe the appropriate treatments for a given application. • Macular degeneration A comprehensive overview of the safety issues, regulations and • Retinal vein occlusion procedures is outside the scope of this review, but these are • Iridectomy covered in more detail elsewhere56,57. • Corneal ablation Future directions Dermatology & Plastic Surgery - Pulsed dye, Laser technology has made rapid progress over the last decade, ruby, KTP, CO , Nd:YAG, diode, alexandrite 2 and lasers have found a niche in many surgical specialities. As IPL • Vascular & pigmented lesions technology advances, it may be that this modality will replace the • Laser ablation & resurfacing laser in some applications. A key advance would be an equivalent • Hair removal to the Q switch, which would allow substantially greater and more • Photo-rejuvination focussed power delivery in one pulse, thus extending the range of • Tattoo removal therapeutic applications of IPLs to include those of Q-switched • Excision of burns lasers. Pain Therapy - Diode • Acute pain therapy Acknowledgements • Chronic pain Ann Allan at the Laser Training and Education Centre, • Wound healing Nottingham and William James at the Laser Unit, Department of Plastic Surgery, Morriston Hospital, Swansea. Oncology - CO2, KTP, Nd:YAG, KTP, Gold vapour • Tumour excision/biopsy Conflicting Interests - None declared • Photodynamic therapy (PDT) • Palliative tumour ablation References 1. Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation), Table 2: Selected applications of lasers in surgery. Physol Z, 1917; 18:121-128)

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Bencini PL, Luci A, Galimberti M et al. Long-term epilation with long-pulsed 1986; 6:38-42 neodymium:YAG laser. Dermatol Surg 25: 175-8 45. Reid WH, McLeod PJ, Ritchie A, Ferguson-Pell M. Q-switched ruby laser 20. Imayama S, Ueda S. Long- and short-term histological observations of congenital treatment of black tattoos. Br J Plast Surg 1983; 36:455-459 nevi treated with the normal mode ruby laser. Arch Dermatol 1999; 135:1211-8. 46. Goldman L. The argon laser and port wine stain. Plast Reconstr Surg. 21. Ueda S, Imayama S. Normal-mode ruby laser for treating 1980; 65:137-9 congenital nevi. Arch Dermatol 1997; 133:355-9 47. Becker DW. Use of the carbon dioxide laser in treating multiple cutaneous 22. Anderson RR, Margolis RJ, Watenabe S, et al. Selective photothermolysis of neurofibromas. Ann Plast Surg 1991; 26:582-6 cutaneous pigmentation by Q-switched Nd:YAG laser pulses at 1064, 532 and 48. Nehal KS, Levine VJ, Ross B, Ashinoff R. Comparison of high-energy pulsed 355 nm. 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Br J Dermatol 1997; 136:360-3 §and tattoos: a microscopic analysis of laser tattoo interactions. Br J Dermatol 52. Troilius A, Troilius C. Hair removal with a second generation broad spectrum 137:405-410 intense pulsed light source - a long-term follow-up. J Cutan Laser Ther 26. Taylor CR, Anderson RR, Gange RW, Michaud NA, Flotte TJ. Light and electron 1999;1:173-8 microscopic analysis of tattoos treated by Q-switched ruby laser. J Invest Dermatol 53. High-intensity flashlamp photoepilation. A clinical, histological, and mechanistic 1991; 97:131-6 study in human skin. Arch Dermatol 1999; 135:668-676 27. Reid R. Physical and surgical principles governing carbon dioxide laser surgery on 54. Kokosa J., Eugene J., Chemical Composition of Laser - Tissue Interaction Smoke the skin. Dermatol Clin 1991; 9:297-316 Plume. Journal of Laser Applications, 1989 July:59-63. 28. Dumon JF, Shapshay SM, Bourcereau J et al. Principles for safety in application 55. Wenig, Barry L., Kerstin M. 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The Evolution of Corneal Refractive Surgery D. L Oladiwura, E. Oki, M. Stanford Medical Eye Unit, St Thomas’ Hospital, London SE1 7EH. United Kingdom. Correspondence to: Mr Miles Stanford, Consultant Ophthalmologist, Medical Eye Unit, St Thomas’ Hospital, London SE1 7EH. United Kingdom.

Refractive errors are some of the most common ophthalmic disadvantages, requiring as it does, manual dexterity to insert and abnormalities worldwide and are associated with significant being associated with sight-threatening complications such as morbidity with recent population-based studies identifying them corneal ulcers and severe infection1. as the leading cause of visual impairment worldwide.1 In North America for instance, as many as 1 in 5 people have some degree In the last 30 years, surgical procedures aimed specifically at of myopia while several studies suggest up to 50% of the altering the focusing or refractive properties of the eye have led to population may be hyperopic.2 Traditionally, spectacles have been the development of what many now consider a bona fide surgical the mainstay of treatment. However, in cases where the patients specialty in the field of ophthalmology. The range of surgical suffer from severe myopia, hyperopia or astigmatism, eyeglasses techniques for the rectification of refractive errors has been have proven less than satisfactory for reasons such as optical diverse, pioneering, and daring. The evolution of refractive distortion or significant inconvenience.3 With the objective of surgery as a subspecialty has been driven by consumer/patient improving on these shortcomings, contact lenses were introduced enthusiasm, a vigorous response by the ophthalmic profession, an in 1960, but even this revolution in management is not without its enormous investment by the technical industry, and a relatively

34 The Journal of Surgery • Volume 2 • Issue 1 • 2004