Biomedical Engineering Reference
In-Depth Information
typical depth-related color changes seen during CO
2
resurfac-
ing also do not occur during modulated Er:YAG resurfacing.
Therefore, when resurfacing with the modulated Er:YAG
lasers, the surgeon must carefully choose clinically appropriate
laser parameters based on anatomic considerations and the
desired depth of tissue ablation. For example, the epidermal
thickness of the eyelid is approximately 60
(coagulative and ablative) Er:YAG laser. One year postopera-
tively, Tanzi and Alster noted no cases of delayed hypopigmen-
tation in their series of 50 patients resurfaced with the Contour
Er:YAG laser (295).
Sapijaszko and Zachary, however, reported two cases of
hypopigmentation in their series of over 100 patients resurfaced
with a modulated Er:YAG laser (Contour) (285). Kim et al.
resurfaced 190 patients of Fitzpatrick skin type III-V with
Er:YAG lasers and observed an incidence and mean duration of
hyperpigmentation of 24.7% (6.5 weeks), 42.3% (7.3 weeks),
and 65.9% (7.8 days) with the short-pulsed, variable-pulsed
(CO
3
, Cynosure), and dual-mode (Contour, Sciton) lasers,
respectively. The incidence and mean duration of hypopigmen-
tation observed were 8.0% (4.4 months), 15.3% (5.3 months),
and 24.4% (5.7 months) for the short-pulsed, variable-pulsed
(CO
3
, Cynosure), and dual-mode (Contour, Sciton) Er:YAG
lasers (274). Goldman and Fitzpatrick have resurfaced over
1000 patients with the variable-pulsed Er:YAG laser (CO
3
,
Cynosure) and have not yet seen a case of prolonged hypopig-
mentation resulting from treatment with this particular laser
(personal communication).
Topical photochemotherapy and the excimer laser have
both been reported to be effi cacious in the treatment of laser
resurfacing-induced hypopigmentation. Grimes et al. reported
moderate-to-excellent repigmentation in fi ve of seven patients
(71%) treated biweekly with a mean number of 25 sessions of
topical photochemotherapy with 0.001% methoxypsoralen
(55). Friedman and Geronemus reported 75% improvement
of laser resurfacing-induced hypopigmentation in two patients
treated with the 308-nm excimer laser for 8-10 treatment ses-
sions. Initial treatment was performed at the minimal ery-
thema dose minus 50 J/cm
2
. If erythema was not seen 24 hours
after the fi rst treatment, the dose was increased by 50 mJ/cm
2
until erythema occurred. The average cumulative UVB dose
was 1750 mJ/cm
2
. They observed no complications and good
retention of pigment at 1-month follow-up (56).
In summary, the modulated (coagulative and ablative
modes) Er:YAG lasers have been able to produce “CO
2
-like”
clinical results with a side-effect profi le that has turned out to
be considerably more favorable than that of the CO
2
lasers.
m. Using the
modulated Er:YAG lasers at a fl uence of 15 J/cm
2
and 30%
overlap, the entire epidermis of the eyelid can effi ciently be
removed in a single pass.
μ
Modulated Er:YAG Lasers: Complications
Overall, the side effect profi le of the modulated Er:YAG lasers
has been reported to be slightly more than that of the short-
pulsed Er:YAG laser but considerably more favorable than that
of the CO
2
laser. As with the CO
2
laser, potential complications
include prolonged postoperative erythema, pigmentary dis-
turbances, scarring, and infection.
Prolonged Erythema
Prolonged postoperative erythema, thought to be related to the
degree of thermal damage and depth of ablation, can occur in
up to 20% of patients treated with the CO
2
laser. Most studies
have reported a decreased duration of postoperative erythema
and a shortened recovery period after resurfacing with the mod-
ulated (coagulative and ablative) Er:YAG lasers as compared
with CO
2
laser resurfacing. Alster et al. resurfaced 50 patients
with a dual-mode Er:YAG laser (Contour, Sciton Corp.) and
found that reepithelialization was complete in an average of
5 days, and only three patients (6%) experienced prolonged
postoperative erythema (295). In a split-face comparison of
16 patients following pulsed CO
2
and variable-pulsed Er:YAG
laser skin resurfacing, Rostan et al. reported decreased erythema,
less edema, and faster reepithelialization on the side treated with
the variable-pulsed (CO
3
, Cynosure) Er:YAG laser (26).
Postoperative Hyperpigmentation
Transient postinfl ammatory hyperpigmentation is not uncom-
mon following modulated (coagulative and ablative) Er:YAG
laser skin resurfacing. However, the reported duration of hyper-
pigmentation after modulated Er:YAG resurfacing has been
shorter than that observed after CO
2
laser resurfacing (16,296).
Jeong et al. reported hyperpigmentation in 8 of 35 (29%)
patients (Fitzpatrick skin types III-V) treated with a variable-
pulsed Er:YAG laser for pitted acne scars. Similarly, Alster et al.
reported a 40% incidence of hyperpigmentation in their series
of 50 patients resurfaced with a variable-pulsed Er:YAG laser.
In both series, the hyperpigmentation was transient and
responded well to topical agents. In their series of 20 patients
with pitted acne scars, Jeong et al. reported an incidence
of hyperpigmentation of 60% and an incidence of hypo-
pigmentation of 5%, following resurfacing with the dual-mode
Contour Er:YAG laser (Sciton Corp.). In all cases, the hyper-
pigmentation was transient and resolved within 3 months
postoperatively (297).
combination co
2
and e
:yag laser treatment
Necrotic tissue directly dysregulates wound healing and
induces proteases and infl ammation. Many experts believe
that the thermally induced zone of necrosis left behind by the
CO
2
laser is one of the main factors contributing to its adverse
sequelae including prolonged postoperative erythema, pain,
delayed healing, and scarring. Therefore, some authors have
investigated the effect of removal of this residual zone of ther-
mally damaged tissue after CO
2
laser resurfacing.
Goldman and colleagues studied the effect of Er:YAG laser
resurfacing aimed to remove the residual zone of thermal
damage left behind after CO
2
laser resurfacing (31). They
randomized 10 patients to receive resurfacing to one-half of
the face with a 950-
r
s pulsed CO
2
laser (three passes, 300 mJ,
CPG settings of 596, 595, and 584) and resurfaced the other
side of the face with two passes of the same CO
2
laser at the
same settings followed by two passes with a short-pulsed
Er:YAG laser (4-mm spot, 1.7 J, 14 J/cm
2
). They found
that both the reepithelialization time and the duration of
μ
Delayed Permanent Hypopigmentation
Delayed permanent hypopigmentation, a common side effect
after CO
2
laser resurfacing (15-20% reported incidence), has
not been reported in most series that utilized a modulated
