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Lip Teh
December 2005
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LASER
History
1916: Einstein - laser theory
1959: Theodore Maimon - first laser using ruby crystal
1960: Ruby crystal lasers used for retinal detachments
1966: Argon laser for cutaneous vascular lesions
1984: Sterling Baker – laser blepharoplasty
1995: Roberts – CO2 laser resurfacing
Physics
LASER = Light Amplification by Stimulated Emission of Radiation
 Laser energy is created by the stimulated emission of radiation
 When an atom achieves an excited state they begin to emit photons these
atoms then collide with a another excited atom stimulating emission of
another photon and these photons travel at the same frequency along the
same axis
 Light converted to narrow intense beam of coherent light with a specific
wavelength
 Medical lasers span from UV to IR
 Creating a laser beam requires 3 parts
1) energy source – electrical, light or another laser
2) medium “lasing” – when stimulated by high energy, produces excited
photons of a specific wavelength
a)
gas laser, ie CO2, Argon
b)
solid state lasers – uses a crystal to generate a beam ie
YAG, Ruby
c)
dye laser – medium are organic dyes with fluorescent
bands dissolved in a solvent
3) laser cavity -mirrors – amplifies the photons, one totally and another
partially reflective
 External power source used to excite the atoms of the lasing medium
this results in atoms being in an excited state.
 The excited atoms are reflected back and forth between the mirrors in
the laser cavity.
 Random spontaneous emission initiated as energy is delivered to the
lasing medium.
 This energy in the form of photons is reflected sand multiplied within
the cavity. A Portion of the light is passed through a partially reflective
mirror producing a laser beam. The beam is then delivered through a
fibro-optic or a hand piece
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December 2005
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The resulting light has the qualities of coherence, monochromacity and
intensity
Natural light has all the colors and wavelengths in the visual band of the
electromagnetic spectrum. Laser is monochromatic ie uniform
wavelength and thus able to target specific tissue
Distinctive Features
1) Collimated – all waves parallel with minimal divergence
2) Coherent – all waves in phase in both space and time
3) Monochromatic – uniform wavelength determined by medium
4) Intensity –photons produced by a laser are greatest per unit area than
any other light form
Electromagnetic spectrum
Ranges from gamma rays to radio waves
Most clinical lasers are in the visible spectrum (400-700nm)
The therapeutic use of the laser depends on the energy delivered to the
tissue and the mode in which it is delivered
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December 2005
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Measurements
Energy – Joules
Power – strength of beam in Watts (J/s)
Power density – power/spot size (Watts/cm2)
Fluence (Energy density) - energy/spot size (Joules/ cm2)
Vaporisation threshold - minimum energy density required to vaporize
tissue
Modes
 CW (continuous wave)- uninterrupted beam of light
 Pulsed mode - long-pulsed (thousandths of a second) or short-pulse
(millionths of a second)
 Q switching – one mirror is made temporarily non reflective. When the
mirror is made reflective the stored energy in the lasing medium is
emitted as a pulse of light 10 billionths of a second in length. Allows
production of light pulses with much higher peak power than in
continuous wave
Laser-tissue interaction
1) Reflected
a. Safety hazard
2) Scatter and/or Refracted
a. A problem if treating small spot sizes
3) Transmission
a. Causes effects on deeper tissue (unwanted effect)
4) Absorption
a. Causes tissue heating (clinical effect)
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December 2005
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The extent of thermal effect is influenced by the following
1. absorption of the light by the chromophore
2. diffusion of the heat to the adjacent tissue
Factors that determine the extent of the thermal damage are
1. energy density
2. pulse duration
3. heat conduction
Longer wavelengths require greater fluences but are absorbed more deeply
Effects are
1) Thermal (primary action)
2) Mechanical
a. Thermoelastic expansion when pulse duration shorter than
TRT generating acoustic waves
Tissue effect
aim - ablate (vaporize by boiling) target tissue, while minimizing thermal
damage to surrounding tissues
determined by
1) Energy density
2) Pulse duration
3) Heat conduction (Tissue type)
Tissue types
Thermal relaxation time – amount of time required for it to cool to half its
peak temperature = length of time for a specific tissue during which thermal
effects are confined to the target tissue with little conduction to surrounding
tissue
Skin: 700-1000µs for CO2 laser
Capillaries: 10µs
Venules/Arterioles: >100µs
Port wine stain: 100-500µs
Melanosomes: 10-100ns
Chromophores – target substances within tissues capable of absorbing light
i.e Haemoglobin, Melanin, Xanthophyll, Water, Collagen
primary chromophores in the skin are Hb, melainin and H2O
When a particular wavelength has a predominant chromophore in the skin it
is highly absorbed by it and minimal scatter occurs
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December 2005
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Selective photothermolysis theory
a)
Appropriate wavelength that is maximally absorbed by
the target tissue and minimally absorbed by adjacent
non-target tissue.
b)
The exposure time of the laser light (pulse widthduration of the pulse) limits the thermal diffusion if the
pulse width is less than the thermal relaxation time off
the tissues
Thermally induced damage to the epidermis and papillary dermis has limited
the treatment of cutaneous lesions. Various cooling techniques such as icing
and h2o have been used to limit the skin damage
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December 2005
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Skin Resurfacing
Target = Water
Aim = obliterate facial rhytides and tighten skin
Epidermis
 Vaporizes at 100ºC (90% water)
Dermis
Elastin
 heat stable
Collagen I
 structural derangements at 50-60ºC (skin contraction)
 irrerversible destruction 60-70ºC (new collagen formation)
 Collagen contracts by approximately 15-25% during carbon
dioxide lasing, producing a shrunken form that serves as a
template for tighter, more organized new collagen formation
2 lasers with water chromophore
a) CO2
b) Erbium:YAG (yttrium-aliminium-garnet)
Histology
Epidermis
 Correction of epidermal atrophy, actinic atypia with
reestablishment of epidermal maturation
 Normalisation of skin pigmentation/melanin distribution
Dermis
 Elimination of abnormal, clumped elastin and proliferation of
normal, thin elastin
 Orientation of collagen fibers in Grentz zone changed to parallel,
thicker band
2
CO resurfacing histo changes similar to phenol peeling
Indications
1) fine wrinkles – esp. periorbital and perioral area
2) deep wrinkles – best used in combination with other techniques
3) acne scarring – superficial pits
4) rhinophyma
5) surgical scar
a. need to perform during collagen remodeling phase (6-8 weeks)
b. red scars – pulsed dye or long pulse green lasers
6) exophytic skin lesions – seb keratosis, xanthelesmas, syringomas
7) pigmented lesions (Er:YAG, Q-switched YAG, ruby)
8) laser blepharoplasty
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December 2005
9) hair transplantation – to make recipient holes/slits
Main disadvantage – initial cost and maintenance
CO2 laser
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wavelength 10600nm
Water absorption coefficiency 800/cm
Vaporisation threshold – 4-5J/cm2
Thermal injury zone 75-150µm/pass
Ultrapulse – high pulse energy with pulse width <1ms
Penetration depth 0.2mm , collateral damage 0.2-0.7mm
15-25% collagen contraction
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December 2005
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 Single pass more superficial than phenol or high conc TCA
 Mostly a thermomechanical reaction that destroys dermal vessels and
denatures dermal proteins
 Computer pattern generator
 Greater control, faster and more predictable
 Coagulates, seals small nerve endings and lymphatics
 Advantage: long-term skin tightening and improvement of facial rhytides
is unparalleled
 Disadvantage: marked erythema persists for several weeks or months and
permanent hypopigmentation occurs at a rate that is unacceptable to
many patients. Even without complications, the early period of recovery
until full reepithelialization can leave the patient housebound for up to 2
weeks.
 Best when combined with superficial peel or Er:YAG lasers for milder
areas
Er:YAG laser
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Wavelength 2940nm
Water absorption co-efficiency 12800/cm
Vaporization threshold – 1.6J/cm2
Penetration depth 0.1mm , collateral damage 0.2-0.5mm
Pulse width 250-350µs
1-2% collagen contraction
MAXIMUM absorption by water thus very little surrounding damage
(10x more efficient than CO2)
Unlike CO2, more of a photomechanical reaction.
Absorption of the energy causes immediate ejection of the desiccated
tissue from its location at a supersonic speed, creating a characteristic
"popping" sound. This translation of Er:YAG laser energy into
mechanical work is an important factor that protects the surrounding
tissue; minimal thermal energy remains to dissipate and cause collateral
damage.
Because of this, higher pulse durations possible (>thermal relaxation
time)
Good for resurfacing
May be used with co2 lasers
Advantages over CO2
1) More precise (smaller injury zone)
2) Faster healing
3) Treat thinner areas with less appendages
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December 2005
4)
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BUT
1)
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5)
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Less redness
Less blotchiness
Less pain
Better for use in patients with darker skin
no coagulation - may make it difficult to gauge depth
laser completely absorbed in wet field
not so good for deeper rhytides
less skin thightening (less deep thermal effect)
more passes required for same effect
Advantages of combined CO2 and Er:YAG
 decreases the lines of demarcation and textural differences
 use on the eyelids causes less coagulative dermal damage and results in
reepithelialization in almost half the time than after the carbon dioxide
laser alone
Flash-lamp pulse dye laser
 Dye lasers contain fluorescent dyes that are dissolved in solvents such as
water or ETOH. The solvent absorbs the light at one wavelength and
emits in another
 flashlamp pulsed dyed laser can be changed over a wide band of the
electromagnetic spectrum(400-1000nm) by changing the dye and
delivered at a short single pulse at high peak powers
 The 585nm wavelength is well absorbed by Hb and less by other
chromophores
 The pulse duration is 450microsecs and this closely matches the thermal
relaxation time for blood vessels in the dermis
 Thus useful for cutaneous vascular lesions such as port wine stains,
superficial hemangiomas and telengiectasia
 Long pulse dyed lasers
 Wave length -595 nm – is the treatment of choice for P-W stains and
vascular lesions
 Not effective for larger caliber vessels as longer pulse width required
YAG laser
(yttrium aluminium garnet)
several yag lasers used in plastics
1) neodymium:YAG
2) KTP(potassium-titanyl-phosphate)
3) Erbium
Neodymium:YAG
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December 2005
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 1320 nm
 No specific cutaneous chromophore
 best suited for mild wrinkles, but multiple treatments are required over
many weeks to achieve an optimal result.
 Non- ablative resurfacing - Can induce a certain degree of thermal
collagen coagulation in the papillary dermis while generally sparing the
epidermis
 Good haemostatic effects
 Good for thick nodular port wine, bulky hemangiomas and deep vascular
tumours
 Tattoos
KTP-YAG
532 nm
oral mucosal and tongue tambours
Q- switched alexandrite
701-826 nm –
used for tattoos with green blue pigment
Argon
Two wavelengths emitted
488 and 514 nm
used for vasc malformation
but hypopigmentation was side effect due to its competing chromophore
melanin
now supplemented by the FLPD
Copper vapor
Two wavelengths – 578(yellow) and 511 (green)
The 578nm coincides with the peak absorption of oxyhemaglobin and
melanin -511nm
Used for port wine and telangiectasia
Ruby
 694 nm and well absorbed by melanin
 treatment of endogenous and exogenous pigmented lesion ie traumatic
tattoos or decorative ones
 long pulse version is used for hair removal
 main complication: hypopigmenation
Technique
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December 2005
Safety
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Burns, eye injury and fire
Safety glasses dependant on type of laser
Sandblasted stainless steel eye shield for patient
Non alcoholic prep
Wet drapes
Sandblasted instruments to prevent reflection
Patient selection
 Assess skin type
o CO2 not suitable for darker skin colors, thin severely sun
damaged skin, ectropion
o Look for history of cold sores, candidal infections, keloid scarring.
 Contraindications generally related to problems with reepithelization
(resulting in hypertrophic scarring)
1. Fitzpatrick skin phototypes 5-6
2. Recent isotretinoin (alters skin appendiceal structure and function) >6months after return of skin oiliness moisture
3. Recent reticular dermis-level resurfacing procedure within preceding
2-3 months
3) Skin Irradiation (past acne treatment)
4) Significant eyelid laxity
5) Excessively thick or thin skin
6) Localised scleroderma (morphea)
7) Burns or other scars
8) Areas with minimal appendages (neck and hands)
9) Area affected with herpes zoster in the past
Medications
1) Pretreatment (6 weeks prior)
a. retinoic acid 0.05-0.1% cream (0.5-1 g Retin-A) in evening
(faster epithelialisation)
b. hydroquinone 2-4% cream (reduce hyperpigmentation, not
required in Fitzpatrick 1 )
c. Alpha-hydroxy acid 2-4% cream (0.5-1 g Exfoderm) in
morning
d. Sun protection cream
2) Antivirals
a. Laser is a potent stimulator of herpes simplex activation.
Recommend all patients to take antivirals 1-2 days prior for
10days or until reepithelialisation complete.
b. Choices are: acyclovir (400mg tds), valacyclovir 500mg bd,
famciclovir 250mg od
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December 2005
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3) Steroids to reduce oedema
a. IV dexamethasone during surgery
b. Prednisolone 100mg/day for 3 days
4) Antierythema (erythema lasts 6 -12 weeks)
a. 1% hydrocortisone (beware cellulites)
b. intralesional steroids if indurated
5) Antihyperpigmentation
a. Appears in darker skin types 2-4 weeks post
b. Bleaching agents as soon as healed
6) Antipruritic
a. Hydroxyzine as required
7) Sunscreens
8) Antiacne
Methods
 Treat by cosmetic unit
 Usually multiple passes required – depends on skin thickness, severity of
rhytides, skin pathology (ie rhytides vs rhinophyma) and operator
experience
 Combine CO2and Er:YAG to feather out edges and minimize thermal
damage
o 1st pass with CO2 – ablate epidermis
o Subsequent passes with Er:YAG (minimize damage to deep
dermis)
 Relationship between number of laser passes and tissue ablation/thermal
damage is not linear.
o The first laser pass significantly ablates more tissue than the
second or subsequent passes; an ablation plateau is reached in 3-4
passes, limiting ablation depth to approximately 250 mm.
However, thermal damage is cumulative with each additional laser
pass, resulting in a wider zone of necrosis.
 Eyelid resurfacing often is performed last because eyelids are treated at
lower pulse settings and densities and require additional care to avoid
burning the eyelashe
 feathering of margin between resurfaced and nonresurfaced skin edges to
prevent demarcation lines (blend by feathering at a reduced fluence or
use Erbium laser)
Post Op
 Keeping the wound moist promotes faster reepithelialization
 Closed vs Open wound management
o Closed - Apply semiocclusive biosynthetic dressing until
reepithelialization is almost complete. (polyurethane films,
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December 2005
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hydrocolloids, hydrogels). Disadvantages are the increased cost,
increased rate of infection, and need for frequent office visits.
o Open – Use occlusive ointment (emmolient). Avoid use of topical
antibiotics (eg, bacitracin [Polysporin]) because of increased risk of
contact dermatitis. Disadvantages are that it is more painful, it is
messy, and it requires patient compliance.
Complications
Early
1) Infections
a. Bacterial, viral, fungal
2) Swelling
3) Contact allergic dermatitis
a. Secondary to ointments/creams used (i.e bacitracin, Vaseline)
b. Treat with 1% hydrocortisone
4) Irritant dermatitis
a. Bleaching agents, sunscreens
b. Avoid irritant, 1% hydrocortisone
5) Erythema
a. Lasts for 10 weeks on average (3-4 weeks with Er:YAG)
b. related to increased blood flow, collagen remodeling,
inflammation, and increased metabolic activity.
c. more obvious in patients with lighter skin complexion
d. Avoid topical steroids to treat postresurfacing erythema since they
reduce collagen synthesis
6) Acne breakouts
a. due to occlusive ointments
b. treat with topical retinoic or glycolic acid, oral tetracycline
c. caution with oral isotretinoin
Late
1) Hypertrophic scarring
a. Risk factors: (1) depth of resurfacing achieved, (2) development of
infection, (3) postoperative wound care, and (4) other patientrelated factors (eg, excoriations).
b. Localized persistent erythema with or without pruritus should be
considered an evolving hypertrophic scar until proven otherwise.
c. Aggressively treat with high-potency topical steroids or
intralesional steroid injections. Silicone sheeting, pulsed dye laser
may be useful adjuncts
2) Ectropion (1%), scleral show (2-8%)
a. treat with canthopexy
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December 2005
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3) Synechiae (2 deepithelialised areas heal in contact causing fold)
a. Avoid with taut dressing
b. Treat by cutting epithelial bridge
4) Hyperpigmentation
a. Up to 38% in CO2 resurfacing, commoner in darker skin
b. Normal process of healing – activation of melanocytes migrating
from appendages to new epidermis
c. Occurs early , usually temporary (<2 months)
d. Treat with hydroquinone 2-4% twice per day, retinoic acid (0.50.1%) every bedtime, and sun protection
e. Preconditioning the skin with retinoic acid and hydroquinone
prior to carbon dioxide resurfacing decreases incidence, severity,
and duration of hyperpigmentation
5) Hypopigmentation
a. Up to 30% with CO2 resurfacing
b. Occurs late – 6-12 months after
c. More obvious with dark skin and regional (vs full) resurfacing
d. Not associated yet with Er:YAG laser
6) Sharp demarcation lines
7) Telangiectasia and capillary fragility
a. esp cheeks and infraocular area
8) Tooth enamel injury
9) Corneal abrasion/injury:
Results
907 patients (CO2 resurfacing) by Roberts et al 1997: 65.2% excellent, 27.2%
very good and <1% poor.
Forehead usually needs combination therapy
Periorbital responds well
Perioral area high risk of hypertrophic scarring
Tatoo Removal
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December 2005
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