Historically,
people
in many societies have searched for
methods to restore youthful appearance and rejuvenate aging skin:
1. Stories about mythical substances
2.During the
3.
Dark Age
Modern
society
The desire for cosmetic enhancement
risk and rapid recovery
means
of
wrinkle
and
of facial skin with
minimal
laser-mediated
photodamage reduction.
has inspired
More recently,
the spectrum of skin issues for which these
methods have been utilized has expanded past the treatment of
photo-aging to include many skin problems more common in youth,
such as
pigmentary disorders
scarring.
and
acne
Laser
use on the skin has become
most popular methods
facial appearance.
one of the
for achieving a younger and smoother
Unfortunately, the increasingly widespread availability of cosmetic laser
therapy coupled with attendant publicity has created extraordinary, often
unrealistic, expectations.
Many patients may believe that lasers are magic wands, capable of
restoring their skin to the flawless perfection of infancy. Of course, the
truth is that cosmetic lasers are not the answer for all dermatologic ills.
‫نمی بخشند ابی‬
‫‪‬‬
‫به زور و زر میسر نیست این کار‬
‫‪‬‬
‫سکندر را‬
While
with
lighter
skinned individuals are more likely to present
deep-seated wrinkles,
darker patients
finer
wrinkles, mottled hyperpigmentation, and
unique skin lesions
actinic lentigines .
are usually seenwith
such as dermatosis papulosa nigra and
patients with Fitzpatrick skin
types IV-VI respond
to
UV injury by producing more melanin. Thus, they
are at higher risk for the development of
resurfacing procedure.
dyschromias
after a laser
for skin types IV to VI is not
contraindicated, resurfacing on these persons can be more difficult
Although laser resurfacing
postinflammatory
hyperpigmentation. This usually begins approximately
1 month postoperatively and lasts about 2 months on
because of the almost certain occurrence of
average, but can somerimes last as long as 9 months.
The
Glogau
physician determine
classification
the
depth
thus offers some indication
system
helps the
of damage,
of what the depth of resurfacing
and
should
minimal photo-damage may require
ablation of only the upper part of the epidermis. Those
with moderate photo-damage
may require more
be. Patients with
extensive resurfacing
and so on.
to the level of the papillary dermis,
The word
LASER
light amplification
by the
is an acronym, which stands for
stimulated emission
of
radiation.
Laser light has unique properties that allow it to be used
therapeutically. Consequently, the popularity of laser procedures has
skyrocketed in the past decade as the indications for use
and types of lasers available continue to multiply.
Laser light is monochromatic
(single wavelength), coherent
(in phase, both in time and space), and collimated (light
waves are parallel). These properties make possible the
generation and delivery of high fluence (energy per area),
which can interact with the skin. Additionally, the monochromaticity
laser light is essential for selective targeting of structures
the skin that preferentially absorb light of that wavelength.
of
in
The endogenous chromophores of importance are:
melanin,
hemoglobin,
water,
and collagen
.
In normally epidermis, absorption is usual in the range of200-10000nm
and for dermis in the range of 280-1300.
Rejuvenation
. ablate
the
and provide
· ablate
epidermis, cause
a significant
thermal
the epidermis,
wounding, and
short-pulsed
effect
(e.g. CO2 lasers)
cause dermal
provide
Er:YAG
dermal wounding
minimal
lasers)
cause
thermal
effects
(e.g.
dermal wounding
· ablate
the epidermis,
and provide
variable
thermal effects (e.g. combined
COrEr:YAG
lasers, variable-pulsed Er:YAG
lasers, and ablative radiofrequency
devices)
.do not
ablate
wounding,
the epidermis,
and provide
lasers and light sources) .
cause
dermal
minimal thermal effects
(e.g. nonablative
Ablative resurfacing was first introduced in the mid
1990s.
In an effort to decrease the risk/side effect profile, the use of erbium
lasers
was explored (Zachary 2000) .
Carbon
lasers
dioxide
The endogenous chromophores of importance are:
melanin,
hemoglobin,
water,
and collagen
.
.Producing a wavelength of I 0,600 nm, the CO2 laser
penetrates approximately 30 nm into the skin by the absorption
and vaporization
water
of
-containing tissues.
The epidermis is composed of 80% water. At the energies used for
resurfacing, instant heating of water to 100°C occurs and vaporization of tissue
ensues.
The thermal
relaxation time(TRT) the amount of time required
for a material to lose 63% (1/e) of its heat by thermal diffusion. If
energy is
delivered to a target in a period of time faster than the time it
takes for the target to lose its heat by conduction to its
surroundings, then no (or minimal) thermal damage will occur beyond the
target.
To achieve heating and destruction of target tissue in a period of time that is
shorter than TRT the laser beam must be pulsed such that it is only on for a time
t < TRT.
A chromophore is heated by laser light absorption in a time period
shorter than its thermal relaxation time.
The latter is the amount of time required for a material to lose 50% of its heat by
conduction to its surroundings.
Thus, when a chromophore is heated by selective photothermolysis, only
the
intended target is damaged and there is minimal diffusion of heat and
no consequent injury to the surrounding structures. The mechanism of injury
involves both thermal coagulation and/or photoacoustic
injury in the form of supersonic high pressure shock waves. For both the CO2
predominant mechanism is
photothermal.
and Er:YAGlasers, the
.Energy
densities of approximately 5J/cm2
order to achieve tissue ablation.
.With each subsequent laser pass, vaporization of
must be applied in
very thin (20-30
nm) layers of skin occurs, leaving a small amount of residual thermal
necrosis. With each subsequent laser pass, further tissue
ablation occurs, but, because the area of residual thermal
necrosis increases (effectively reducing the amount of tissue
water
and hence the
targeted chromophore), the
amount of
ablation with each pass diminishes until a peak of approximately 100 nm is
reached.
.Delivering more than three to four passes, or the use of excessive energy
densities, significantly increases the risk of excessive thermal injury
and subsequent scarring.
The pulse fluence necessary to achieve vaporization and thus ablation of skin
tissue with the CO2 laser is 5J/cm2. This can be calculated based on two factors:
The latent heat of vaporization of water is 2500J/cm3, and the energy
(Ev)absorbed per unit volume of tissue is Ev= fluence x µa. The depth of
penetration of the 10,600nm wavelength has been calculated to be 20µm, or
l/µa, where µa is the absorption coefficient for water (equal to 500cm-1).
Solving for fluence in the above equation, fluence = 2500/500 = 5J/cmz.
The actual thickness of tissue ablation varies from 20 to 60nm.
Cutaneous CO2 laser resurfacing, as currently performed, has been shown to
be highly effective in the treatment of photo-damaged skin. In addition to
superficial ablation,
there is a "tissue tightening" effect following
use of these lasers. This effect is thought
to be related to
heat-
induced collagen shrinkage, which occurs maximally at 63°C.
Long-term collagen remodeling and
neocollagenesis also occur after resurfacing, although the mechanisms
behind this are not fully known.
It is believed that these effects result from
thermal desiccation
associated with the concomitant collagen shrinkage. In
addition, because there is increased expression of smooth
muscle actin after laser treatment, the contracted area may serve as a
scaffolding on which new collagen is formed and deposited during wound
phase remodeling.
These factors are most likely responsible for the long-term clinical
improvement seen after resurfacing.
Significant
least
collagen
shrinkage
two passes.
and remodeling
requires at
Several CO2 laser systems are available and can be separated into two
distinct groups:
pulsed and scanned.
The high-energy pulsed CO2 lasers (e.g. Ultrapulse, Lumenis)
produce single, short (1 ms) pulses o fvery high energy (up to 7 J/cm2).
A computerized
pattern generator (CPG) attached to the laser
delivery system can rapidly and precisely place 2.2S-mm spots in
any of several patterns while maintaining appropriate ablation
parameters.
A large square pattern can be used to treat large areas rapidly. The
density
of the pattern can be low (nonoverlapping spots) or high (1060%overlapping spot)
BOLOGNIA:
The first type is the high-powered pulsed CO2 laser system, which delivers
energy in individual pulses of about 1 ms or less (e.g. UltraPulseM).
This laser produces up to 500 mJ of energy in each individual 600
µS-l ms pulse. Vaporization can be performed either with a 3 mm
spot size or by a computer pattern generator, which can deliver
various patterns of up to 80 pulses, each pulse measuring 2.25 mm in
diameter.
Scanned laser
systems (e.g. FeatherTouch, Lumenis; Silk- Touch,
Lumenis) utilize a computerized scanning device to deliver lower power
CO2 laser energy in the continuous mode rapidly over the skin,
thus limiting the tissue dwell time in one area. This
system achieves high peak powers by focusing the laser beam to small
spot size, and rapidly scans the focused beam over a predetermined
geometric pattern, exposing the individual tissue sites for less than 1ms.
BOLOGNIA:
The second type of CO2 resurfacing laser achieves well-controlled tissue
ablation by rapidly scanning the focal spot of a focused
continuous-wave
CO2 laser over the skin (e.g. FeatherTouch
and
SilkTouch
flash scanners). Computer-driven
mechanical devices can
scan a 0.2 mm spot in a spiral manner, ranging in diameter from 8
to 16 mm in several shapes at a constant velocity. No individual spot
is irradiated more than once and the dwell time on any individual spot
is less than 1 ms, while achieving fluences above the ablation threshold.
UltraPulse laser (Coherent)
and the SilkTouch scanner (Sharplan).
2 more popular CO2 lasers are
WHAT IS DWELL
TIME?
Laser dwell time is the amount of time that the beam is
on in one location.
Low power densities require longer dwell times to achieve
the same effect as high power densities. The longer the dwell time
and the slower the heating, the more desiccation and
charring of tissue that results. Further heating of charred tissue results
in extremely high temperatures of 300-600°C. This is because carbonized and
desiccated tissue acts as a heat sink for laser absorption. There is no buffer
of water to absorb the heat and thus temperatures escalate rapidly.
Continuous wave lasers must be rapidly scanned across the
treated area in order to keep the dwell time less than the thermal relaxation time.
A study comparing four different CO2 lasers found that pulsed
systems produced the least amount of thermal necrosis with the
greatest subsequent collagen formation (compared with the scanned
systems), but equivalent clinical outcomes between all four lasers were
observed.
BOLOGNIA:
In general, two passes with the SilkTouch are
approximately equal to three pulses with the UltraPulse
and four passes with the FeatherTouch in terms of the
amount of tissue removed and the depth of residual thermal damage.
(A) To generate identical fluence at skin surface, a chopped pulse (continuous
wave) must be maintained for a longer period than with ultrapulsed or
superpulsed lasers, which generate a higher peak power over a shorter time. (B)
Comparison of ultrapulse, superpulse, and chopped-pulse CO2 laser fluence. At
same average power, superpulsed laser must deliver 4 to 5 pulses for each ultra
pulse. A chopped pulse is seven times longer than an ultra pulse for this same
energy.
CW CO2 LASER:Because the peak powers were low (the same as the
average power, or 10–30 W), the power densities were often subablative
or
marginally supra-ablative, and the only advantage was confinement of
thermal injury to a level not observed with longer exposures (and
higher fluences).
The shortest possible exposures available with these devices were typically 50–
100 ms.
The next generation of CO 2 lasers used so-called “superpulsed
(SP)
technology”. Pulses were on the order of 50–200 mJ and were delivered with
varying repetition rates (50–500 Hz).
The term “UltraPulse,” used by a leading manufacturer, refers to a
subset of superpulsed lasers with a rectangular pulse
profile, capability of low repetition rates, and higher peak
powers than older first-generation SP lasers.
The short-pulsed
Er:YAG laser was developed in the mid 1990s in
an
attempt to replicate the results of the CO2 laser
minimizing the side-effect profile
while
. The
emitted wavelength of 2940 nm has a higher affinity for water and is
therefore absorbed 12 to 18 times more efficiently by superficial cutaneous
tissues. Approximately 2-5 µm of ablation occurs per pass, with very
narrow zones of thermal necrosis. Clinically, this translates into a
shorter postoperative healing time with a
lower risk of post-treatment erythema
and hyperpigmentation than with CO2
lasers.
Fleming has shown that to achieve equal depth of injury the Er:YAG
must ablate deeper than the CO2 laser because there is minimal
laser-induced thermal damage. Hence, multiple passes with the
laser are necessary to ablate a similar depth as one
pass of the CO2 laser.
With the
Er:YAG laser at 2940nm, the energy is so efficiently
absorbed by water (12-18 times that of the
l0,600nm wavelength) that its narrow depth of penetration (2-5 J/m)
results in a very superficial layer of tissue ablation with minimal
surrounding thermal injury (20- 50J/m compared to
60-100J/m for CO2).
high absorbance in tissue, the
Because of this
Er:YAGlaser achieves ablation primarily through a
photomechanical rather than a photothermal
effect.
1)In addition, because
the
photomechanical
CO2), intraoperative
achieve.
Er:YAG
effects are
photothermal (like the
hemostasis is often difficult to
rather than
The thermal damage zone created by this procedure
is fixed
and very small. In fact, this thermal damage is so shallow
that it is insufficient to coagulate dermal capillaries. This explains why
Er:YAG-lasered skin bleeds. 2)The lack of thermal
damage may also be considered a disadvantage when treating patients
with severe wrinkles.
3)Other
limitations
include the associated
large amount of plume
noise level
produced.
and the
1)minimal surrounding thermal injury
2)poor hemostasis
3)
Reduced collagen shrinkage
.The Derma-K is a hybrid that combines a conventional
ablative
Er:YAGwith(short pulse) a low-power CO2 laser for
coagulation.
.The dual
mode Contour consists of two Er:YAGlaser heads. One
delivers short-pulsed ablative energy and the other provides longpulsed subablative coagulative energy.
.The CO3 laser is a variable pulse system that delivers both
short
ablative and long coagulative pulses from the same
Er:YAGlaser head.
Extensive prepping of the skin prior to laser
treatment is unnecessary because the heat of the laser
sterilizes the skin.
The treated areas should
be wrapped with wet towels to
decrease the risk of fire.
Preoperatively, patients apply topical anesthetic cream
EMLA (eutectic mixture of lidocaine and
prilocaine) with occlusion
procedure time.
Forty-five minutes
2.5 h
prior to the
before the procedure,
EMLA is reapplied with occlusion.
.The
first CO2
ablative laser
pass
is performed mainly to
remove the epidermis and feather peripherally to
minimize any demarcation with surrounding nontreated skin.
.The
second laser pass, and, if used, a third pass is for heat
deposition to promote tightening.
.Finally, the erbium laser (in the ablation mode) can be used to
remove superficial thermal necrosis for further
deeper rhytides and/or acne scars.
Sculpting: to make sth a particular shape
sculpting of
When the UltraPulse CO2 laser specifically is used, the
pass
first
is usually performed at a density of 7 for the main
treatment areas. The previously described preoperative topical
anesthetic technique leads to increased skin hydration
and, consequently, allows the use of a higher density setting to
more efficiently remove the epidermis.
If no hydration is used, the
density of
first pass is performed at a
6.
Overlap:10%
Hair-bearing areas must be avoided, including eyebrows
and eyelashes.
Hydration is mandatory, however, for treatment of the
neck.
Mandatory: comulsory , necessory by the
law
When moving towards the jawline and hairline, the density is
decreased to 6 and possibly 5 for higher risk patients. Thus:
For initiating:-7 if hydration is performed(neck should be hydrated
necessarily)
-6 if hydration is not performed
-6 in jawlines(5 if the pt is highrisk)
-Progressing down the neck, density settings are
decreased by one per row until the lowest setting
of 1 is reached, allowing skip areas in the final row.
NECK:INITIATING WITH 7 AND
REACHES TO 1 IN THE LOWEST ROW
The epidermis is then wiped free on the central face and
other areas where a second pass is to be performed. The peripheral
edges are usually left intact and the neck is never wiped.
NECK:INITIATING WITH 7 AND REACHES TO 1
IN THE LOWEST ROW AND SHOULD NOT BE
WIPED
WIPE:to rub sth against a surface to remove dirt,liquid,etc.
The wet
gauze also serves to rehydrate the desiccated tissue.
Dry gauze should be used to remove any remaining water
and exudates prior to another pass because this surface water would absorb
the energy and prevent further tissue ablation.
The second CO2 laser pass is performed at a density of 4–5 depending on
the tightening needed and the risk for the area.
.The upper eyelids and the central face are typically treated at
5
,whereas mid cheeks and some lower eyelids may be treated with
densities of 4.
NOTE:
.Delivered energies are also decreased towards the
periphery.
densities of
.A second pass is rarely done on the lateral cheeks unless acne
scarring is present.
third pass may be done on acne scars and in perioral and
glabellar regions to deliver additional heat to enhance tightening.
.A
.When using the EMLA topical anesthetic technique, the face is typically
treated in sections. All passes in a given area are performed before moving on
to the next section.
.Always 'feather'
the peripheral areas by decreasing the density
of pulse application as well as the pulse energy (decrease to 200-250m), or angle
the beam at 45 degrees to spread the fluenee over a larger surface area.
.Feather into the hairline a distance of 5-15 mm and well under the
jawline (3-5 cm).
Computer pattern generator (CPG) settings should not use densities greater than
6??? if cumulative thermal damage from excessive pulse overlap is to be
avoided.
FITZPATRICK:
in general, thinner
skin (e.g., periorbital) requires
fewer laser passes, and laser resurfacing of non-facial skin
(e.g., neck, chest) should be avoided due to the
relative paucity of pilosebaceous units in these areas
The
endpoint of treatment is when one of the following conditions is seen:
1. The wrinkle
or scar is removed.
2. A yellow-brown discoloration indicating thermal damage is
seen.
3. No
further skin tightening is observed
deep rhytides or acne scars persist,
laser in the ablative (shorter-pulsed) mode is
In cases where
the
erbium
helpful to
sculpt the edges or to remove the superficial coagulative necrotic layer, which can
hinder healing. The utilized erbium laser energy, and spot size, depends
3.5- to 5.0-mm spot
size set at 1–2 J/cm2 most commonly used.
on the area to be treated, with a
Bleeding can occur in these areas as the thermal effect is insufficient to
provide hemostasis.
One
should not continue ablation once the
distinctive
yellowish color of the desiccated
reticular dermis has been reached.
erbium laser is the sole utilized
system, the first pass is performed to most efficiently debride the epidermis.
When the
This is undertaken typically at 100 µm of ablation with no coagulation.
The ablation depth is decreased at the periphery to minimize the final
demarcation between treated and untreated areas. For
the second
pass, erbium laser coagulative pulses or, alternatively,
ablation with concomitant coagulation is used to provide the heat
needed for the tightening effect. Finally, the third pass utilizes the
ablation mode to remove superficial necrosis but can also include
additional coagulation to enhance the thermal effect.
. To treat the neck, pure ablation
is used with a
graduated drop in setting to feather while proceeding lower and laterally on
the neck. As with the pulsed CO2 laser, careful feathering to blend the treated
and untreated areas is critical to ensure a natural and cosmetically pleasing result.
As with CO2 ablation, the area to be treated should be wrapped
with wet towels. Eye protection with intraocular anti-reflective
metal eyeshield(s) should be used if treating the eyelid .Wiping between
laser passes is unnecessary because proteinaceous debris is
ablated with each subsequent pass.
Patient preparation
and anesthesia are performed similarly to those
for the CO2 laser. However, because the Er:YAG laser causes minimal
pain, less anesthesia may be necessary for many patients,
and topical and local anesthesia will suffice.
The fluence required for ablation using the Er:YAGlaser is
1 J for every
4µm of tissue vaporized. One adjusts the fluence to an appropriate setting for
the amount of ablation desired. A
tluence of 10J/cm2 will reliably
vaporize 40 J/m of tissue, thus ablating epidermis in about two passes. The
endpoint is visible effacement of the lesion(s) or until reticular dermis has been
reached.
Because of the relative lack of visual cues as to the
depth of ablation, one must keep track of how many
passes have been delivered once the papillary
dermis has been reached.
With the Er:YAG, approximately
per J/cm2
4 µmof tissue is vaporized
of energy applied. Therefore, a fluence of 5 J/cm2 will
ablate the epidermis in four passes. Settings can be adjusted,
depending on the depth of ablation desired. A repetition rate from I
to 10 Hz and spot sizes from 3 to 7 mm can be selected with most
Er:YAG lasers.
With the traditional Er:YAG, bleeding may prevent deeper ablation. However,
rapid pulse stacking can allow deeper ablation by ablating the accumulating
blood along with additional tissue. Bleeding may be controlled with
or with soaks
pressure
of 1% lidocaine and epinephrine. In this case,
the surface must be dried prior to the next pass to prevent surface
water absorption by the laser.
Various spot sizes can be used. Repetition frequencies of I-10Hz with spot
sizes of 3-7mm are typical. One should use 50% overlap of
spots either freehand or with a computer pattern generator (CO2
LASER ovrlap spot:10 -60%)
long Pulse Er:YAG
The Cynosure C03 utilizes a variable pulse Er:YAGlaser (0.5-l0ms) to effect
ablation and coagulation. The long pulse duration may be below the tissue
vaporization threshold resulting in thermal coagulation effects approaching those
of short-pulsed CO2 lasers. The endpoint is similar to CO2 lasers with
vaporization of epidermis and papillary dermis to leave behind coagulated collagen
indicated visually by a visible yellow color. The color change is more
subtle with the Er:YAGlaser, even given the long pulses delivered for coagulation.
The amount of thermal damage is intermediate between that obtained using purely short
pulsed Er:YAGlasers and resurfacing CO2 lasers. Also, wiping between passes
rehydrates the tissue and can eliminate the yellow color. The Cynosure CO3
laser has been shown to result in less thermal necrosis than both the Sciton optically
multiplexed Er:YAG laser and the CO2 laser but with approximately equivalent
clinical efficacy. Settings
used with long-pulsed
Er:YAGlasers are generally similar to the short pulsed
Er:YAGlaser. Ablation at a setting of 10J/cm2 fluence will vaporize 40J/m per
pass.
Freehand technique or use of a scanner may be performed. When performing
freehand ablation, 50% overlap of spots and pulsing at 5 Hz or more efficiently
removes tissue equivalent to two passes without overlap.
BOLOGNIA:
Overall
efficacy of the Er:YAG is rather similar
to the CO2 laser, although the CO2 laser has been found
to be superior in most compar- ative studies. The Er:YAG laser has
been associated with
less tissue tightening
or
contraction
as compared to the CO2 laser, which may
impact the long-term outcome in photoaged skin.
variable-pulsed Er:YAG laser (pulse durations
of 10-50 ms) demonstrates immediate tissue contraction and a
The
is intermediate between the short-pulsed
Er:YAG (pulse durations of 250-350 µs) and CO2 lasers.
healing rate that
In comparative studies, the variable-pulsed
Er:YAG laser was very
effective in the removal of rhytides, although the CO2 laser was
still found to be slightly more efficacious.
Ablative
histologic
resurfacing
with the CO2 and Er:YAG lasers results
neocollagenesis
postoperatively.
evidence of
6 weeks
Early on, however, the inflammatory
approximately
cell infiltrates differ,
band-like infiltrate of neutrophils
following CO2 treatment as opposed to a mild
perivascular infiltrate of neutrophils and
eosinophils following Er:YAG treatment.
with a
in
.Studies indicate that closed wound care regimens utilizing
dressings for 48-72 h postoperatively
reepithelialization and reduce crusting, discomfort,
occlusive
may hasten
erythema, and swelling.
.Pain management using this technique may require only acetaminophen.
Dilute acetic acid soaks several times per day (a
capful of white vinegar in
a pint of warm water makes an approximately 0.25% acetic acid solution) to
Move Exudate and debris followed immediately by application of moisturizing
ointments such as Aquaphor Healing ointment, Theraplex, Crisco, or Catrix-I0.
There are few true contraindications. A personal or family history of
vitiligo should be considered a relative contraindication. Theoretically, a
Koebner phenomenon could occur and bring out vitiligo in the laser-treated areas.
Scleroderma
patients should be counseled that ablative resurfacing
could exacerbate their disease, although reports of successful treatment exist (T.
Alster, personal communication).
Darker-skinned patients need to understand the likelihood of
hyperpigmentation, which is usually temporary but may be long-lasting. The use of
hydroquinone preparations with vitamin A derivatives, glycolic acid and/or topical
corti- costeroids, and good sunscreen minimized this problem. Patients with very
fair and fine-pored skin appear to be at greatest risk for delayed
hypopigmentation, which can be permanent.
Unrealistic expectations and inability or unwill- ingness to perform wound care are
contraindications for ablative skin resurfacing.
BOLOGNIA:
history of keloids, radiation therapy to the
area or scleroderma are not candidates. Diseases
that exhibit koebnerization,
such as psoriasis and
vitiligo, are relative contraindications. Prior isotretinoin
therapy has been associated with
Patients with a
atypical scarring after dermabrasion
or chemical peeling, even if the
procedure were performed more than I year after isotretinoin treatment1. Therefore, it is generally recommended
that
patients wait for at least 1-2 years before undergoing
this procedure. Resurfacing performed at the same time or soon
after facelifting or blepharoplasty increases the risk of skin necrosis
and scarring due to the altered blood circulation of the undermined
skin following these procedures.
Hence, laser resurfacing of undermined
skin should be
deferred for at least 6 months after the original
surgical procedure. Laser resurfacing is not used on the
neck and chest due to the unacceptably
high risk of scarring.
hands,
By targeting water as a chromophore,
induces a
the
1550-nm erbium
fiber laser
dense array of microscopic, columnar,
do not perforate or
impair the function of the epidermis. In
thermal
zones of tissue injury that
addition, for every MTZ (microthermal
zone, or microscopic
treatment zone) that the laser targets and treats intensively, it leaves the
surrounding tissue unaffected amd intact.
heal much faster
than if the entire area were treated at once, owing to the presence
of residual viable epidermal and dermal cells.
This "fractional" treatment
allows the skin to
The stratum corneum remains intact during the process,
thereby maintaining epidermal barrier function.
BOLOGNIA:
This approach thermally
ablates
leaving intervening
of normal skin that
a fraction
of the skin,
regions
serve to rapidly repopulate
the ablated
columns of tissue.
cylindrical areas of thermal
epidermis and upper dennis, which
It causes
density of approximately 1000-3000
photothermolysis
per cm2.
damage
to the
are spaced at a
microscopic treatment
zones of
BOLOGNIA:
As in ablative laser resurfacing,
the areas of thermally
ablated tissue
fibroblast neocollagenesis and
epidermal proliferation. In contrast to ablative resurfacing,
fractional resurfacing provides faster recovery and fewer side
effects, with resolution of erythema and edema within a few days in
are repopulated
by
most patients. However, the improvement in rhytides and
photodamage
is not as impressive as with ablative resurfacing. Mild
to moderate improvement requires multiple (5-61 treatment sessions at 1- to 4-week intervals.
Pigmentary
improvement
comparable to that
seen with pigment-specific Q-switched lasers and
IPL, but acne scars and wrinkles appear to improve
faster and to a greater extent than with the nonablative devices.
is
intelligent
The fractional laser contains an
optical tracking system
that utilizes OptiGuide Blue 1M tint, a water-soluble Federal Food, Drug, and
Cosmetic Act (FD&C) dye. The optical mouse in the laser handpiece
recognizes subtle differences in the density of blue dye
on the skin's dermatogliphs. The mouse communicates with the laser to lay
down an even MTZ spot pattern independent of handpiece velocity. This
system allows for a more even placement of MTZs, which is important in
fractional tissue treatment where the optimal spacing between lesions
allows for rapid re-epithelialization
and prevents negative sequelae
associated with fully ablative treatment at depths of 300-800 flm.
Using the 15-mm handpiece on the 1550-nm erbium-doped fiber
laser (Fraxel, Reliant Technologies), it is recommended
that facial
skin
receive
eight passes at a fluence of 8 mJ/cm2
density of 250 MTZ/cm2 to an endpoint
of approximately
2000 MTZ/cm2, or approximately3 kJ. Treatment
consecutively every 3-4 weeks until desired
achieved.
Clinical improvement
and a
may be used
results
are
is greatest 3 months
series of fractional photothermolysis
after a
treatments ,a finding that stands in
contrast to results seen after purely non ablative, mid-infrared
lasers where optimal efficiency was obtained 6 months after treatment.
Each column
or 'microthermal
150 µm in width
400-700µm
zone' is
approximately
with a vertical thermal
into the dermis.
70-
injury depth of
FITZPATRICK:Microscopic epidermal
necrotic debris
exfoliates over the next several days, producing a bronzed
appearance to the skin.The wound healing response differs from the
response after the use of ablative techniques because the epidermal tissue
that is spared between thermal zones contains viable transient amplifying
cells capable of rapid re epithelialization.
Furthermore, because the stratum corneum has a low water
content, it remains intact immediately after treatment.
Therefore, the wound createdby fractional resurfacing is unique not
simply that of an ablative laser used to make "holes" in the skin.
The biological response to the laser resurfacing wound raise the question of
whether a treatment could be devised that would
stimulate the remodeling response discussed above without
removing or ablating tissue or creating an open wound with all
the associated risks and inconveniences .Essentially, the goal of this
nonablative remodeling (also called subsurface remodeling) treatment as it
came to be called was to separate the two modalities of clinical improvement and
rely solely on remodeling without any tissue removal .Several strategies were
devised utilizing a laser
pulse of energy directed to the mid-
dermis with a synchronized cooling application to
protect the epidermis and upper dermis from injury.
unpredictable outcomes associated
with non-ablative remodeling treatment and the undesirable
Frustrations with the
recovery associated with ablative laser resurfacing led to the
development of fractional treatments as an extension of this
approach. The skin surface is exposed to a succession of
thousands of
microscopic beams of light each of which is separated
from the neighboring beams whether applied sequentially or
simultaneously. The skin underlying each small beam of light was
coagulated but not ablated.
By limiting the diameter of the wounds created and the total percentage of
skin exposed in a single treatment, the depth of treatment could be
extended safely to less than that which was associated with scarring in classical
wounds.
The limited
nature of the tissue iniury
and the large
reservoir of unwounded tissues surrounding each
area of exposed tissue allow rapid
healing with a
minimum of risk compared to all preceding photothermal laser therapies There
has been considerable research performed as to how the MTZ heal. They appear
extrude the desiccated tissue from the
surface leaving behind reiuvenated collagen.
to
The concept behind this approach is to thermally alter a fraction of the skin,
leaving intervening areas of normal
skin untouched, which rapidly repopulate the
ablated columns of tissue.
The 1550-nm erbium-doped mid-infrared fiber laser induces cylindrical areas of thermal
2000 microscopic
treatment zones of photothermolysis per cm
(1000-3000)
damage to the epidermis and upper dermis spaced at
Each column is approximately 70
to 150 microns in width and induces
vertical thermal injury of 400 to
700 microns in depth into the dermis, referred to as
‘‘micro thermal zones.’’ These zones comprise
approximately 15% to 25% of the skin surface area per treatment session.
Similar to ablative laser resurfacing, the areas of thermally ablated
tissue are repopulated by fibroblast activity of neocollagenesis and
epidermal stem cell reproduction. As compared to ablative resurfacing, fractional
faster recovery and fewer
side effects.
resurfacing results in
What is the the outcome of fractional laser in
comparison with other lasers?
.
erythema and edema resolve
within a few days in most patients, the
1-Although
improvement in rhytides and
photodamage is not as impressive as with
ablative resurfacing.
2-Pigmentary improvement is similar to that seen with
pigment specific Q-switched lasers and IPL photorejuvenation, but
acne scars and wrinkles appear to improve faster and
to a greater extent than with the other nonablative
techniques.




1. Acne scar and wrinkles:
Ablatve resurfacing>Fractional>Nonablative
2.Pigmentory lesions:
Fractional=Nonablative
Acne scar and wrinkles:
Ablatve resurfacing>Fractional>Nonablative
requiring
multiple
treatment sessions, totaling 5
spaced at 1- to 4-week intervals.
to 6 and
(Sun-induced pigmentary alteration improves more quickly, while wrinkles
require more treatments to see significant improvement.)
The need
for quicker results has led to
development of
a parallel
ablative fractional resuffacing. Carbon
dioxide and erbium wavelengths are available with others such as YSGG to
come.
Typical fractionated devices have spot sizes in the range of 75-750 pm
How large the spot size can become while preserving the rapid healing of skin
even with deep treatments is unclear but is likely to be 750 pm or less . Early
work by the authors compared three spot sizes for fractional erbium lasers
including round 250pm, round 750pm and square 430pm and failed
to
show a difference in healing times between these
spot sizes.
Results were similar but may be slightly better with the larger spot
sizes. Second, spacing
between laser exposures must be preserved to
some degree.
Clinical experience shows that depth
of non-ablative fractional
resurfacing needs to be deeper than with ablative devices to see
clinical results Quantification of this is not known at this time . Increased density
or closeness of ablation channels appears to improve results.
Optimal density is not known and its relationship with spot size not known.
Fraxel SR (Reliant Technologies) was the
aforementioned 1550-nm erbium fiber laser which was approved for use at
40 J/cm by the FDA in 2003 for soft tissue coagulation, periorbital
rhytides and pigmented lesions in 2004, and skin resurfacing and
The original
melasma and acne and surgical scarring in 2006.
The new addition is the Fraxel SR1500, which was approved by the FDA in
January 2007 at 70 mJ/cm. This dose allows for greater penetration depth (up to
1.4 mm) as compared to the 300- to 800-micron depth attained previously, and is
aimed at treating deeper rhytides.
In addition, the Fraxel AFR, a fractionated CO
deeper penetration depth, is currently in development.
2 laser that provides a
Competitors in fractional resurfacing include the Lux 1540 Fractional
(Palomar Medical Technologies, Burlington, Mass), a 1540-nm pulsed device
which is approved by the FDA for soft tissue coagulation.
This device contains a handpiece that divides pulsed light into microbeams
which penetrate up to 1 mm. The advantages of the Palomar system include the
practicality and versatility of a handpiece
that attaches to its
pulsed light and laser system and the fact that it is painless.
Another version of fractional resurfacing by the same manufacturer is a
noncoherent infrared light source, which generates pulses in the 825 to
1350 nm range of the spectrum (Lux IR Fractional infrared handpiece
attachment for the StarLux pulsed light and laser system). This technology
delivers an array of small beams that create a periodic lattice of isolated
hyperthermic columns ranging from 1.5 to 3.0 mm in diameter to the reticular
dermis.
Finally, a Lux2940 fractional laser handpiece has been added, using
delivery of erbium laser light to deliver very deep ablative columns
Another fractional resurfacing device is the Affirm laser (Cynosure Inc,
Westford, Mass), which sequentially emits 1320-nm and 1440-nm wavelengths at fixed
intervals. A microlens array is employed to diffuse the laser light into a lattice of
microbeams, with targeting of superficial and deeper penetration depths through
the two wavelengths.
Finally, a fractional CO 2 with versatile settings is also under investigation
(Mixto, DEKA).
every type of laser or light-based
treatment is being re-examined to determine
Nearly
if it would benefit from fractionated delivery The indications,
efficacy and advantages of this approach are unproven, though promising, for
these other application areas.
Common
indications
for fractionated lasers in the
near and mid-infrared range include treatment of acne
scars,
hlpertrophic scars, and traumatic scars .Many effects of
photoaging can also be treated including particularly rhytids and solar
lentigines and to a lesser extent skin laxity and vascular changes
(e.g. telangiectasias) Specifically melasma
but also other pigmentory
disorders that manifest both superficial and deep
placement of pigment are amenable to correction. Any other
indication that would be improved by skin
resurfacing could also potentially benefit from these treatments.
Patients with dyspigmentation
and lentigines require 2 to
3 treatments, whereas those with significant rhytides require at least 5 or
more treatment sessions.
Patients with melasma require multiple
treatments, and long-term follow-up is needed to properly assess how effective this
treatment is for a recalcitrant condition that has a high recurrence rate with other
modalities. Given the report of hypertrophic scarring following ablative
resurfacing in a patient with a history of recent isotretinoin use, we currently
12-month waiting period following
discontinuation of isotretinoin before commencing
fractional resurfacing.
recommend a
All patients, regardless of whether they have a history of herpes labialis, receive
prophylactic oral antivirals, such as acyclovir, famciclovir, or
valacyclovir, starting 1
day before fractional resurfacing and
continuing for 5 days postoperatively or until reepithelialization
is
complete. Oral antibiotics, such as dicloxacillin or azithromycin, may be prescribed
to patients with a history of bacterial infections of the facial skin to reduce the
chance of secondary bacterial infection.
Topical anesthesia is required, typically involving the application
EMLA or LMX cream for
60 minutes before the procedure.
During
the procedure, cold air cooling (Zimmer MedizinSystems, Irvine, Calif)
is required to minimize discomfort.
Some of the newer fractional resurfacing devices are reportedly painless.
Topical anesthetics
with the 1450nm
are recommended
prior to treatment
diode and the Fraxel restore laser.
Dry
gauze is used to remove the anesthetic cream and a blue dye applied
(original Fraxel protocol) in order to optimize contrast for the optical scanner,
which is a component of the device. Newer versions of the Fraxel device (and
newer fractional resurfacing devices) do not require blue dye application. A
thick layer of gel is then reapplied and treatment begins.
The standard treatment parameters employ
8-10 mJ/Fraxel
and a Fraxel
density of 250/cm . The treatment time is approximately 20 to
30 minutes to treat the entire face.
Approximately 8
passes are conducted over each treatment
area, to generate a total Fraxel density of 2000/cm. The face is cleaned
with soap and water and moisturizer applied.
By 24 h, the lower epidermis and basal cell layer are
restored, and microscopic epidermal
necrotic debris
(MEND) has formed.
keratinocytes and melanin that
migrate upward through viable keratinocytes at the margin of the
MEND represents damaged
MTZ,
and is
extruded by day 7.
MEND formation
is associated with a
clinically, which
can
mild bronze color
persist for several weeks.
The current
Fraxel re:store1M laser protocol
involves
anesthetic, followed by application of a thin layer of
a topical
LipoThene gel to the treatment area. Reflections
from
the lubricant
are used to sense handpiece
motion.
The use of anesthetic
or
too much
gel can impede
treatment.
The handpiece is held
perpendicular to the skin, and rolled evenly along the skin .
Adjacent
tracks should
not be overlapping,
and multiple
passes are used to achieve the desired coverage.
Superficial lesions such as lentigos are treated with lower
energy levels, and deeper lesions such as acne scars with
higher energy levels. Less auxillary
cooling may be used to
optimize
treatment
coverage)
debris are
swab.
the treatment
of superficial targets. If more aggressive
is desired, treatment levels
(corresponding to percentage
are increased . After treatment, gel, smudges, and
removed
from the handpiece
window
with a cotton
oral prednisone 30 mg
the morning of the procedure and an additional dose the
subsequent two mornings following the procedure
if edema persists.
Some advocate the administration of
Areas that heal more slowly than the face can be safely
treated using fractionated treatments due to the faster healing and high
risk cases can often also be treated safely.
As treatments are performed 2-4 weeks apart and collagen may take many
months to rejuvenate the final results may not be seen for
months after stafting treatment.
several
In cosmetic
dermatology, there are three main area of clinical
aging which all have to be accessed when planning a holistic facial rejuvenation:
(1) lines and wrinkles (i.e., dynamic wrinkles, static wrinkles, and wrinkle
folds), (2) volume loss and loss of facial contour (e.g., loss of
subcutaneous fat in mid-face, with subsequent gravitational folds), and (3)
skin surface and textural changes(pigmentation
changes,impaired skin firmness and
elasticity,atrophic crinkling,crepe-like textural
changes,etc)
all three
Only if
key areas are addressed, a
successful and natural appearing rejuvenation can be
achieved.
Historically, ablative lasers were the optimal
photodamaged skin.
treatment for
However, ablative skin resurfacing has become increasingly unpopular with
significant risks of
prolonged recovery time, possible permanent
both patients and physicians due to the
hypopigmentation,and/or scarring.
Nonablative skin resurfacing has become the treatment of choice for
photorejuvenation. It offers an elegant, effective, noninvasive
treatment for problems related
moderate photodamage).
to photodamage and aging (mild
to
Nonablative
stimulate
lasers attempt
similarly to heat and
the wound healing process in the dermis, but
removing epidermis.
without
This is often referred to as dermal
remodeling, subsurface resurfacing, or laser toning.
In theory, dermal heating should be aimed at
tissue 100-500 µm below the skin surface.
Rejuvenation
. ablate
the
and provide
· ablate
epidermis, cause
a significant
thermal
the epidermis,
wounding, and
short-pulsed
effect
(e.g. CO2 lasers)
cause dermal
provide
Er:YAG
dermal wounding
minimal
lasers)
cause
thermal
effects
(e.g.
dermal wounding
· ablate
the epidermis,
and provide
variable
thermal effects (e.g. combined
COrEr:YAG
lasers, variable-pulsed Er:YAG
lasers, and ablative radiofrequency
devices)
.do not
ablate
wounding, and
nonablative
the epidermis,
provide
cause
dermal
minimal thermal effects
lasers
and
(e.g.
light sources)
.
Ultraviolet-induced photodamage accelerates and magnifies the
physiologic changes of the normal aging process. Ultraviolet exposure produces
a myriad of changes in the skin, including free
radical formation,
apoptosis, angiogenesis, melanogenests, DNA
mutations, oncogenesis, immunosuppression,
matrix metalloproteinase induction, and
degradation of connective tissue. The histologic
manifestations of photodamaged skin include loss of collagen and
abnormal clumping of elastic fibers in the
superficial dermis. In addltion, ultrastructural analysis shows a
thin epidermis, flattened rete,
increased vasculature,chronic
Inflammation,elastotic changes including the accumulation of large amounts of
elastic material, wide spaces between the collagen bundles, and random deposition of
collagen fibers.
Photo-damaged
skin contains
metalloproteinases,
fibrils. Ultraviolet
increased levels of
which degrade and disorganize collagen
(UV) radiation induces free radicals, which further
Damaged collagen is replaced
by increased glycosaminoglycans and
thickened elastic fibers (solar
elastosis). Most of these changes occur between 100
damage collagen.
and 500 µm below the skin surface.
Clinical photodamage is classified into three types.
Type I
photodamage includes telangiectasias, solar
lentigines, increased skin coarseness, and symptoms
of rosacea. Type II photodamage includes rhytides,
dermatochalasis, comedones, and skin laxity. Type
III photodamage includes actinic keratoses,
nonmelanoma skin cancers, and melanoma.
Standard nonablative skin resurfacing is successful in patients with
types I and II photodamage. Generally, photorejuvenation
treatments are undertaken on the sun-exposed areas of the face, neck, upper
chest, and hands.
depth of
penetration , which is reciprocal to the absorption
coefficient of water
(µ water).
Each type of laser is associated with a different
Nonablative skin resurfacing technology can be categorized into four
different general modalities; vascular lasers, mid-infrared lasers,
intense pulsed light systems, and radiofrequency devices.
Recently developed, light emitting diode
role in improving photodamaged skin.
(LED),
devices may also play a
Hemoglobin absorbs light between
577 and 595 nm; the
PDL or a low-fluence potassium- titanyl-phosphate
(KTP) laser can be
used to heat
dermal blood vessels and adjacent
to the endothelium
induction
perivascular collagen.
Damage
may lead to cytokine-mediated
of collagen remodeling.
Melanin is concentrated in the basal layer, located
50-100
Heating melanin may result in
subjacent dermal collagen heating and contribute
µm below the skin surface.
desired histologic changes.
to
Some physicians recommend
that patients stop topical retinoids, a-
hydroxy acids, and vitamin C derivatives 48 h before and after
each treatment.
Relative contraindications are a previous history of skin cancer,
Kaposi's sarcoma, lupus erythematosus, or other photosensitivity.
Patients should wait 6 months
after completing
isotretinoin therapy
before undergoing laser treatment. Individuals with a suntan or
history of keloid scarring should not be treated. Although there is
no scientific evidence regarding this, patients who are pregnant should
not undergo laser treatment.
Patient selection for nonablative skin resurfacing is based on an evaluation of the
individual's degree of photodamage and aging. The ideal patient is 35-55
years old with moderate signs of photodamage and aging.
Conversely, patients with deep rhytides and severe laxity may show minimal to
no response. Such patients may be better candidates for ablative resurfacing or
other more invasive cosmetic techniques.
The exact mechanism of action of pulsed dye laser-induced collagen formation
is unclear. Theoretically, laser- induced damage to vascular
endothelium produces cytokines that lead to dermal
remodeling of collagen and improvement in the appearance of rhytides.
Despite approval by the US Food and Drug Administration (FDA) for treating
photodamage with the LP PDL(595nm), only modest results have been
observed with these short wave-lengths, presumably because of predominantly
vascular targeting and superficial penetration to the papillary dermis.
Recently, the application of the precursor photosensitizer aminolevulinic acid
ALA
(
) in combination with the LP PDL has enhanced the ability of this laser
to treat photoaging.
Photodynamic therapy mediated by LP PDL is effective
in the removal of actinic keratoses (AK), actinic cheilitis (AC),
lentigines, fine rhytides, and textural changes caused
by photoaging.
The mechanism of this effect appears to be the activation by the LP PDL at
595 nm of the photosensitizer protoporphyrin
IX which preferentially
accumulates in photodamaged cells, resulting in their
destruction either by apoptosis or an immune-mediated response. Thus, the
effects of PDL on photodamaged skin have been significantly augmented by ALA
application.
Normally, no topical anesthesia is required.
However, such anesthesia may be applied for
1 hour prior to
treatment especially if hlgher laser fluences are to be used.
Full face treatment without
overlapping pulses is
recommended.
If purpura is noted, the utilized fluence is generally too high.
The
periorbital area is particularly prone to developing purpura
whereas the paranasal area requires higher fluences as compared
with the cheeks.
Nd:YAG lasers are currently available in 1320-nm
long-pulsed,
1064-nm
long-pulsed,
1064-nm short-pulsed,
and 1064-nm Q-switched versions.
This category of laser has been used to benefit photo-damage ,
mild rhytides, and acne scarring, and is historically safe
darker skin types.
in
At
1064 nm, there is weak melanin, hemoglobin, and water
absorption. The absorption by these discrete chromophores is low compared
to vascular-specific and pigment-specific lasers, and the water absortion is
much lower at 1064 nm compared to the mid-infrared wavelengths of 1.3–1.5
mm . Nd:YAG laser irradiation produces deeply penetrating photons into the
dermis due to decreased scattering of light at this wavelength .
The lack of very strong absorbing chromophores coupled with good dermal
penetration results in deep tissue heating.
Skin irradiation at 1064 nm produces volumetric heating of a cylinder of tissue
below the laser pulse, extending millimeters into the dermis . A 5 and 10 mm
spot produce depth of penetrations of 5 and 10 mm, respectively, in skin.
The theory of selective photothermolysis developed by Anderson and Parris
describes the necessary requirements for selective destruction of site-specific targets
in tissue using electromagnetic radiation. Selective targeting of tissue targets
requires (a) the use of a wavelength preferentially absorbed by the chromophore,
(b) a pulse duration less than or equal than the thermal relaxation time (TRT), or
cooling time, of the targeted structure, and (c) sufficient fluence to produce
irreversible damage. In 2001, Drs. Altshules, Anderson, and colleagues proposed the
extended theory of selective photothermolysis , which describes the pulse duration
requirements for nonuniformly pigmented structures in tissue, such as blood vessels
and hair follicles.
When treating a tattoo or pigmented lesion, heating of the structure will destroy the
lesion, and the heat does not flow out of the target until it is fully damaged.
When targeting a nonuniform structure, such as a blood vessel or a hair follicle,
there are portions of the structure that exhibit much greater absorption than
others. The weakly absorbing portions of the structure are then damaged by heat
diffusion from the highly absorbing areas of the structure. In the case of a leg vein,
the blood is the “absorber,” but closure of the vein requires coagulation of the vein wall which
must be heated by diffusion from the blood. Similarly, the hair shaft and matrix cells are
the “absorbers” for hair follicles, but the other follicular tissues including the stem
cells do not contain chromophores absorbing in the near-infrared. Consequently, the
treatment pulse duration for nonuniformly pigmented targets is significantly
longer than the thermal relaxation time, and has been termed the thermal
damage time (TDT).
Water absorption at 1064 nm is weak compared to the mid-infrared wavelengths
used for rejuvenation. The deep
scattering at this wavelength and
relatively weak absorption by the skin’s major chromphores
volumetric heating
results in
of the dermis. When epidermal
cooling methods are properly employed, the dermis is heated without the
creation of an epidermal wound. This results in fibroblast activation and
new collagen production. Electron microscopic analysis of skin following
irradiation with a 1064 nm laser, pulse duration of 300 ms, spot size of 5 mm, and
fluence of 13 J/cm, showed a decrease in the collagen fiber diameter in the
papillary dermis 1 and 3 months after treatment . This finding is consistent with
the deposition of new collagen.
The Nd:YAG laser has two
major emission wavelengths in the nearinfrared range, one at 1064 nm, and another at 1300 nm with selectivity
determined by different optical resonators.
NOTE:Passing the 1064 nm beam through potassium titanyl phosphate (KTP)
crystal in the laser cavity halves the wavelength (i.e., doubles the frequency) to 532 nm,
which is in the green visible light range.
The currently available model of the
1320nm Nd:YAG
accompanied by a unique hand-piece with
laser is
three portals. One portal
contains the cryogen spray that cools the epidermis prior to, during and after
treatment, one
portal emits the l320nm Nd:YAG laser
irradiation, and one portal contains a thermal sensor. Emitted
I320
nm Nd:YAG laser fluences lead to peak measured epidermal temperatures of 4248C. An epidermal surface temperature of 40-48'C correlates with a dermal
temperature of 70'C. This is the required dermal temperature for
collagen denaturation and the subsequent wound healing response. The
handpiece thermal sensor captures the surface T max after the initial test spot
allowing the clinician to adjust the fluence accordingly. For example, T max after
an initial test spot at the setting of 14J/cmz may be 37'C. For optimal results, the
clinician should increase the fluence by 1 J /cmz increments until the surface
Tmax is between 4 2 a n d 4 8 C .
The
1450nm diode laser is quite similar in its effect to the l320nm
Nd:YAG laser. This mid-infrared wavelength laser also vaporizes water in the
dermis, creates an imperceptible wound, and subsequent neocollagenesis for the
treatment of rhytides and atrophic acne scars. The 1450nm diode and
l320nm Nd:YAG laser systems are often used interchangeably with similar
efficacy. However, it remains to be seen whether more specific treatment
parameters will show one to be superior to the other. One study did suggest
the 1450nm diode to be superior in the recontouring of atrophic scars
when used at fluences ranging from 9 to 14J/cm2.
Another study, by Friedman et al, found the 1450nm diode laser damages
sebaceous glands selectively and is effective for the treatment of inflammatory
acne on the back . Finally, a study compared the effect of the cryogen alone to the
1450 nm laser with cryogen cooling and found the laser effect led to significantly
more collagen in the papillary dermis
The 1450nm diode laser utilizes an integrated cooling device that delivers
cryogen before, during, and after irradiation in a manner similar to that seen
with the 1320nm Nd:YAG laser. This laser has a slightly longer emitted
pulse duration of 250ms compared to the 200 ms pulse duration seen with
1320 nm Nd:YAG laser. There is no thermal sensor
in the l450nm diode laser handpiece but generally treatment fluences range
between 9 and l4J/cmz. Theoretically, there should be no epidermal absorption by melanin when this laser is used in darker skin types. However, there is
still a risk of post-treatment hypopigmentation when this laser is used with
skin types V or VI This may be secondary to cryoinjury and/ or nonspecific
energy absorption.
Clinical improvement was correlated with optical profilometry findings but not
with the number of treatments. Perioral sites were least improved.
All in all 2 indications
of 1450 diod laserare:
1.Photorejuvenation
2.Active acne lesions
The 1540-nm erbium-doped phosphate glass laser is another midinfrared range laser that targets intracellular water. This wavelength
has the least amount of melanin absorption compared with
the 1320- and 1450-nm laser systems - an advantage when
approaching darker skin types.
The 1540 nm erbium:glass laser is widely used in Europe for the treatment
of mild to moderate rhytides. As with all mid-infrared lasers, selective
vaporization of water-containing tissue dermis leads to subsequent collagen
remodeling and reduction of rhytides. This laser penetrates up to a depth of
2 mm. Theoretically, this depth correlates with the depth of maximum solar
elastosis. This system differs from the l320nm and l450nm lasers in
several ways:
Instead of a three-phase cryogen cooling system, the 1450 nm erbium:glass
handpiece delivers continuous contact cooling with a sapphire lens cooled to 5'C.
The efficacy of the 1540 nm laser has been demonstrated by photography,
profilometry and ultrasound imaging showing a 40o/o reduction in wrinkles and
a 170lo increase in epidermal thickness at 6 weeks after the fourth treatment . In
another study, histologic evidence of significant dermal remodeling, clinical
satisfaction, and few side effects were noted after treatment with the l540nm
laser.
IPL treatment begins with a consultation to define the patient's goals. The IPL is
combination of essential telangiectasias, solar
lentigines and, less commonly, early rhytides. Parameters are
used for a
selected based on skin type and target tissue. For example, for facial
telangiectasias in a patient with types l-lll skin the initial setting might be
500-560nm filtea l5-20J /cmz,withsingle or double varying pulse duration
delivered pulses. Due to the extensive list of available devices, see each
manufacturer's literature for suggested parameters.
Darker skin types may preclude the use of certain types of nonablative skin
resurfacing. In such patients light sources and lasers that target pigment must be
used with caution and at settings to minimize thermal damage. Side effects
such as blisters, scars, focal atrophy, textural change, and hyper- or
hypopigmentation are all more likely to be seen in darker complected individuals.
Mid-infrared lasers with emitted wavelengths varying between 1320
and 1540 nm target water in the dermis and theoretically can be used safely in
darker skin types.
However, when irradiated at high fluences non- specific laser energy
absorption by melanin can lead to thermal damage and side effects even in
darker skin types. The most common albeit rare side effect experienced by
patients with darker skin color after nonablative skin resurfacing is transient
hyperpigmentation. This is usually seen with those nonablative devices that
utilize cryogen epidermal cooling.
The hyperpigmentation may be due to cryoinjury and can be avoided by
reducing the amount of cryogen delivered with each pulse.
Melanin is concentrated in the basal layer, located 50-100 µm
below the skin surface. Heat- ing melanin may result in subjacent
dermal collagen heating and contribute
to desired histologic changes.
Although protective, the presence of melanin makes it more difficult to
treat photo-aging. Melanin absorption of laser energy can result in
epidermal damage and decrease the amount of energy that reaches the
intended dermal chromophores.
Because the absorption coefficient of melanin decreases as
wavelength increases , nearinfrared and infrared wavelengths can best
provide non ablative rejuvenation for darker skin types. Epidermal cooling is
the most important part of treating ethnic skin; however, too much
cooling can result in postinflammatory hyperpigmentation .
The
most
equipped
popular PDL
with
a cryogen
system
(Candela)
is
device. The handpiece
is held perpendicular to the skin and stamped over the target
areas. Acne lesions may be treated
individually, or the entire face
from
forehead
to jaw
line
cooling
may
be treated.
Q-switched
approximately 2 cm
in a "painting“
The
Nd: Y AG handpiece
is held
away from
the skin, and moved
fashion to cover the entire skin. Because the longer
wavelength
penetrates
deeper,
the Nd:YAG
laser is always kept outside the periorbital rim
to avoid eye damage, even if internal eye shields are worn.
The diode systems use a "stamping"
face, or affected
areas, can be treated
technique.
The entire
with nonoverlapping pulses.
When
using long wavelengths, such as the
diode or Nd: YAG
systems, gauze should be placed inside the mouth to
protect teeth and fillings.
A test spot in a nonauspicious area, such as the preauricular cheek,
should be performed, and parameters adjusted to achieve mild
erythema.
Suggested starting parameters for fair-skinned individuals are listed in
Table 8-2.
The handpiece should be held exactly perpendicular to the skin.
If there is a contact cooling device, the cooling window should be in
complete contact with the skin, and should remain in contact even after
light delivery. The cooling window is cleaned to
remove debris that may heat the window and attenuate the beam. If there
is a cryogen spray cooling system, the handpiece must be perpendicular
to ensure alignment of the cryogen spray and laser pulse . Second passes are
often used to provide subsequent and gentle heating. However, after the
first pass, inflammation ensues. This results in increased perfusion and
temperature, so a second pass over this mileu may result in higher
temperatures and more damage.
The
neck, chest, and hands
are more hazardous. These
decreased sebaceous glands and follicular units, so fewer
stem cells are available for re-epithelialization and wound
healing.
areas have
The science of light-emitting
diodes (LEDs), which emit lowintensity noncoherent light of multiple wavelengths, is new. The
light excites atoms and molecules, resulting in chemical reactionsm that
are postulated to influence fibroblast proliferation. Gentlewaves (Light
BioScience, Virginia Beach, VA) is the first LED to be approved by the FDA
for the treatment of periorbital rhytides. This technology is being explored
for prevention of radiation dermatitis and as a light source for photodynamic
therapy.
Light emitting diodes (LED) are emerging as another method of skin
photomodulation The LED mechanism of action is thought to be through both
new collagen formation and the inhibition of matrix metalloproteinase
activity, the enzyme responsible for collagen breakdown. LED treatment is
provided in a series of biweekly treatments over four weeks.
It has shown virtually no side effects. Ideally, LED treatment is used in
conjunction with other non-ablative modalities to improve signs of photodamage
and to bolster dermal collagen.