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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 39  |  Issue : 4  |  Page : 186-191

Comparison of 1550-nm nonablative fractional laser versus 755-nm picosecond laser with diffractive lens array for atrophic facial acne scars in asian skin: A prospective randomized split-face clinical study


1 Department of Dermatology, Xiamen Chang Gung Hospital, Xiamen, China
2 Department of Dermatology, Xiamen Chang Gung Hospital, Xiamen, China; Department of Dermatology, Chang Gung Memorial Hospital, Chang Gung University; Department of Cosmetic Science, Chang Gung University of Science and Technology; Department of Aesthetic Medicine, Chang Gung Clinic, Taipei, Taiwan
3 National Yang-Ming Chiao-Tung University; Dr. Lin Skin Clinic, Taipei, Taiwan
4 Department of Dermatology, Xiamen Chang Gung Hospital, Xiamen, China; Department of Dermatology, Chang Gung Memorial Hospital, Taoyuan, Taiwan

Date of Submission20-May-2021
Date of Decision02-Sep-2021
Date of Acceptance22-Sep-2021
Date of Web Publication29-Dec-2021

Correspondence Address:
Dr. Sindy Hu
Department of Aesthetic Medicine, Chang Gung Clinic, 4F, No. 9, Ln. 130, Sec. 3, Minsheng E. Road, Songshan District, Taipei City 105

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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ds.ds_38_21

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  Abstract 


Background: Nonablative lasers are popular alternatives for atrophic acne scar treatment in Asia. Objectives: We aimed to compare the efficacy and safety between 1550-nm nonablative fractional laser (NAFL) and 755-nm picosecond laser with diffractive lens array (DLA) in Asian patients. Methods: Twenty-three patients with atrophic acne scars received three sessions of split-face treatment with 1550-nm NAFL on one side and 755-nm picosecond laser with DLA on the other side. Sessions were applied at 8-week interval. Blinded dermatologists assessed efficacy through baseline and follow-up photographs. Results: A greater improvement in atrophic facial acne scars was observed on the 1550-nm NAFL side than on the 755-nm picosecond laser side (P < 0.05). Pain was significantly more severe on the 1550-nm NAFL side than the 755-nm picosecond laser side (P < 0.05). Adverse effects on the 1550-nm NAFL side included prolonged erythema, acneiform eruptions, superficial crusting, and postinflammatory hyperpigmentation. Only transient erythema was observed on the 755-nm picosecond laser side. Conclusion: Although the 1550-nm NAFL showed superior efficacy to the 755-nm picosecond laser with DLA for the treatment of atrophic facial acne scars, the latter was associated with fewer adverse effects and may be the best choice for those who request “little-to-no down-time” treatments.

Keywords: Atrophic acne scar, fractional laser, picosecond laser


How to cite this article:
Lin MY, Hu S, Lin CS, Chung WH. Comparison of 1550-nm nonablative fractional laser versus 755-nm picosecond laser with diffractive lens array for atrophic facial acne scars in asian skin: A prospective randomized split-face clinical study. Dermatol Sin 2021;39:186-91

How to cite this URL:
Lin MY, Hu S, Lin CS, Chung WH. Comparison of 1550-nm nonablative fractional laser versus 755-nm picosecond laser with diffractive lens array for atrophic facial acne scars in asian skin: A prospective randomized split-face clinical study. Dermatol Sin [serial online] 2021 [cited 2022 Jun 30];39:186-91. Available from: https://www.dermsinica.org/text.asp?2021/39/4/186/334162




  Introduction Top


Acne is estimated to affect 9.4% of the world's population, making it the eighth most prevalent disease worldwide. In Mainland China, the overall pooled prevalence rate of acne is 39.2%, and males have a 1.112 times higher prevalence rate of acne than females. Moreover, the prevalence of acne in Southern China is significantly higher than in Northern China.[1] Acne scarring is a long-term complication that can affect up to 95% of patients and have a negative effect on the quality of life. Acne scarring can be emotionally distressing and result in poor self-esteem, depression, anxiety, and even suicide. In addition, a disfigured facial appearance has been associated with social impairment, low academic performance, and unemployment.[2]

Regarding therapies for acne scarring, conventional ablative resurfacing has lost acceptance due to the associated risk of long-term dyschromia (also known as “alabaster skin”), which is aesthetically unpleasant. Alternative therapies have emerged that overcome this pitfall. Nonablative laser has become an ideal option for atrophic acne scars due to its acceptable clinical efficacy, mild adverse effects, and short procedural time. In this regard, the 1550 nm-nonablative fractional laser (NAFL) has been used for the treatment of atrophic scars for over 10 years.[3] An additional 755-nm picosecond laser with diffractive lens array (DLA) has also shown an advantageous resurfacing effect.[4] With the use of 1550-nm NAFL or 755-nm picosecond laser with DLA, the stratum corneum of the treatment site and surrounding skin remains intact after laser irradiation. The therapeutic mechanisms of these two lasers are different. The chromophore of the 1550 nm NAFL is water. It is characterized by the generation of microscopic thermal zones (MTZs), which are subjected to thermal coagulation that damages the epidermis and dermis. The skin surrounding each MTZ is preserved in 1550-nm NAFL and therefore, the damaged epidermis is quickly replaced. MTZs not only induce healthy collagen turnover and remodeling but also act as a significant reservoir of intact dermis and epidermis to improve postprocedure healing.[5] Conversely, the 755-nm picosecond light targets melanin. Laser-heated melanin provides initial free “seed” electrons during the laser pulse, which subsequently cause an “electron avalanche breakdown:” localized plasma vacuoles are formed in the epidermis via electron-molecule collisions, a process termed “laser-induced optical breakdown” (LIOB). It has been hypothesized that the energy absorbed by the LIOBs is efficiently converted into pressure waves that propagate into the dermis. This barotrauma may lead to changes in the dermis, resulting in dermal improvement.[4],[6] In addition, the 755-nm picosecond laser can promote dermal remodeling via alterations in cellular membranes, causing changes in cell signaling and the release of cytokines. This treatment option, which is free from the significant risks of thermal diffusion to the surrounding tissues and possibly from postinflammatory hyperpigmentation (PIH), was initially developed to treat safely individuals with dark skin.[7] The 1550-nm NAFL and 755 nm picosecond laser with DLA have shown promising outcomes in the treatment of atrophic acne scars in Asian individuals. However, to the best of our knowledge, direct comparisons between these treatments in Asian individuals have not been performed to date.

Therefore, we aimed to conduct a randomized, split-face clinical study to evaluate the efficacy and safety of the 1550-nm NAFL and 755-nm picosecond laser with DLA for atrophic facial acne scar treatment in Asian skin.


  Materials and Methods Top


Study design and patients

This was a prospective, randomized, split-face, double-blind clinical study conducted at the Department of Dermatology of Xiamen Chang Gung Hospital from January to October 2020. The study was approved by the ethics committee of Xiamen Chang Gung Hospital, Xiamen, China (IRB number: XMCGIRB2019027). Informed consent was obtained from all participants.

Each participant was randomized to receive a split-face treatment with 1550-nm NAFL on one side [Figure 1]a, [Figure 2]a, [Figure 3]a and 755-nm picosecond laser with DLA on the other side [Figure 1]d, [Figure 2]c, [Figure 3]d. Twenty-three patients (males: 13; females: 10; mean age: 25.52 ± 2.89 years) diagnosed with facial atrophic acne scar were recruited; 21 out of 23 patients (91.30%) had Fitzpatrick's skin type III, and the remaining 2 (8.70%) had skin type IV. Boxcar scars were seen in 65.22% (15/23) of patients, rolling scars in 8.70% (2/23), scattered ice-pick scars with boxcar scars in 21.74% (5/23), all three types in 4.35% (1/23). 26.09% (6/23) of patients have scattered ice-pick scars. Exclusion criteria included the history of any laser treatment on the treatment site during the past 6 months, use of isotretinoin during the past 6 months, hypertrophic scarring or keloid formation, active infection, autoimmune connective tissue disease, diabetes, pregnancy, breastfeeding, and drug, alcohol, or tobacco use.[8],[9]
Figure 1: Comparative photographs of both sides of the face in the same patient. 1550-nm nonablative fractional laser treatment-side (a) at baseline; (b) on the second day after treatment showing erythema and superficial crusting; (c) and at 3-month follow-up, showing a 26%–50% improvement after three treatment sessions. 755-nm picosecond laser with diffractive lens arra treatment-side (d) at baseline; (e) on the second day, showing no adverse effects; (f) and at 3-months follow-up, showing a 1%–25% improvement after three treatment sessions.

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Figure 2: Comparative photographs of both sides of the face in the same patient. 1550-nm nonablative fractional laser treatment-side (a) at baseline; (b) on the third day after treatment, showing acneiform eruptions and superficial crusting. 755-nm picosecond laser with diffractive lens arra treatment-side (c) at baseline and (d) on the third day, showing no adverse effects.

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Figure 3: Comparative photographs of both sides of the face in the same patient. 1550-nm nonablative fractional laser treatment-side (a) at baseline; (b) on the second day after treatment, showing mild erythema and superficial crusting; and (c) at 3-months follow-up, showing postinflammatory hyperpigmentation and 1%–25% improvement. 755-nm picosecond laser with diffractive lens arra treatment-side (d) at baseline; (e) on the second day after treatment, showing no adverse effects; (f) and at 3-months follow-up, showing a 1%–25% improvement in acne scar and improvement of acne-induced postinflammatory erythema.

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Treatment technique and details

After application of a topical anesthetic cream (containing 5% lidocaine cream and 5% prilocaine: Ziguang Pharmaceutical Co., Ltd. Beijing, China), the intervention site was occluded for 30 min using a plastic film. A nonablative fractional 1550-nm erbium-doped fiber laser (Fraxel® DUAL Laser System, Solta Medical Inc., Hayward, CA, USA) equipped with a 15-mm handpiece was used to deliver eight passes of fluences of 70 mJ/microthermal zone (MTZ) on one side of the face, at a treatment level (TL) of 7 (corresponding to treatment coverage of 20%) per treatment session. Total energy of 0.89 ± 0.16 kJ was delivered in each session. A cold-air cooling device (Zimmer MedizinSystems, Irvine, CA, USA) was used at a setting of 5 for all patients.

On the other side of the face, the 755-nm picosecond laser with DLA was applied using a 6-mm spot size, fluence of 0.71 J/cm2, the repetition rate of 10 Hz, and pulse width of 750 picoseconds. The pulses were averaged at 1534.67 ± 50.85.

All subjects received treatment every 8 weeks for a total of three sessions. Immediately after the irradiation, mometasone furoate 0.1% cream was applied once, followed by ice compresses for approximately 30 min. Prophylactic antibiotics were prescribed for the prevention of acneiform eruption: oral doxycycline 100 mg twice daily for 7 days and topical fusidic acid cream twice daily for 7 days. When a patient had a history of herpes simplex virus infection, prophylactic antivirals were given.

Efficacy and safety evaluations

Digital photographs (Visia, Canfield Imaging Systems, Fairfield, NJ, USA) of the faces taken before treatment and at 3-month follow-up were evaluated by two-blinded dermatologists. The investigator global assessment was used, which is based on a 5-point scale (grade 0 = no improvement; grade 1 = 1%–25% improvement; grade 2 = 26%–50% improvement; grade 3 = 51%–75% improvement; and grade 4 = 76%–100% improvement). In addition, patient satisfaction was evaluated. Patients were asked to rate their pain on a numerical scale ranging from 0 (no pain) to 10 (worst imaginable pain) during each treatment session. Other adverse effects, such as prolonged erythema (>4 days), prolonged edema (>2 days), crusting, acneiform eruption, hyperpigmentation, hypopigmentation, herpes simplex virus outbreaks, erosion, and blister were documented.[10]

Statistical analysis

The statistical analysis was performed using SPSS 22.0 software for Windows (IBM SPSS, Chicago, IL, USA). Continuous variables were presented as medians with standard deviations and ranges, and categorical variables were presented as numbers with percentages. We used Pearson's Chi-squared test to analyze the correlation between two categorical variables. A paired t-test was used for the evaluation of differences in paired continuous data. One-way analysis of variance was used for comparisons between groups at each time point. All P < 0.05 were considered significant.


  Results Top


On the 1550-nm NAFL side, 17 patients (73.91%) showed 26%–50% improvement and six patients (26.09%) showed 1%–25% improvement, whereas on the 755-nm picosecond laser side, all 23 patients (100%) showed 1%–25% improvement. Thus, a greater improvement of atrophic facial acne scar was observed on the 1550-nm NAFL side compared to the 755-nm picosecond laser side (P < 0.05) [Figure 1]. The patients' degree of satisfaction paralleled the physicians' assessment. Pain was significantly higher on the 1550-nm NAFL side than on the 755-nm picosecond laser side (7.35 ± 1.12 vs. 2.35 ± 0.92, P < 0.05). Regardless of the specific treatment, pain during the second and third treatment sessions was significantly lower than that of the first session (P < 0.05). Eighteen patients (78.26%) experienced prolonged erythema on the 1550-nm NAFL side, which resolved within 6.61 ± 1.45 days; conversely, only transient erythema (<24 h) was observed on the 755-nm picosecond laser side. Acneiform eruptions were noted in the 1550-nm NAFL side of two patients on the 3rd day after the first session [Figure 2]b. Neither of them had complied with the indication of prophylactic doxycycline. After receiving this drug for 5–7 days, the acneiform eruption resolved. Superficial crusting appeared on the 1550-nm NAFL side and exfoliated 7–16 days after treatment [Figure 3]b. One patient (4.35%) with type IV skin experienced PIH on the 1550-nm NAFL side [Figure 3]c. No crusting or PIH were documented on the 755-nm picosecond laser side. No hypopigmentation, herpes simplex virus outbreaks, erosion, or blisters occurred in any participant.


  Discussion Top


In this split-face, single-blind clinical study, the 1550-nm NAFL demonstrated superior efficacy compared to the 755-nm picosecond laser with DLA for the treatment of acne scarring in Asian patients. However, 755-nm picosecond laser with DLA prevailed over 1550-nm NAFL in terms of adverse effects; the former was less painful, had a shorter duration of erythema, and showed no PIH or acneiform eruptions. A systemic review of 17 randomized clinical trials, including 453 patients, for facial rejuvenation, skin spots, and atrophic acne scars indicates that 1550-nm NAFL seem promising in the short term, with minimal adverse effects.[11] In a case report, 755-nm picosecond laser with DLA demonstrated long-term remodeling effect in the treatment of acne atrophic scars.[12] Further research with better methodological standardization, more scientific evaluation criteria and a longer follow-up evaluation period are mandatory to elucidate long-term treatment efficacies of both 1550-nm NAFL and 755-nm picosecond lasers.

In a previous study, Chrastil et al.[13] used a second-generation erbium-doped 1550-nm laser (Fraxel SR1500, Reliant Technologies Inc.) with the following treatment settings: 15-mm handpiece, fluences 35–40 mJ/MTZ, TLs 7-10 and “Advanced Level 1,” corresponding to a treatment coverage of 20% to 35% and 8–10 passes per treatment session. A total of 2–6 treatments were performed at 1-month intervals. They found that 17.24% of the patients had a >75% improvement, 62.07% a 50%–75% improvement, 17.24% a 25%–50% improvement, and only 3.45% a <25% improvement in acne scarring. Moderate erythema and edema appeared in most patients and tended to resolve within 2–5 days. Chan et al.[14] compared the “full” NAFL treatment (Fraxel SR and SR1500, Solta Medical) with treatment coverage of 25-30% (average 442.5 MTZ/cm2) and delivered in 8 passes, with a low-density “mini” NAFL treatment utilizing half the density (average 210.5MTZ/cm2) and delivered in 4 passes, in Asian patients. The fluence was kept constant in both groups (mean 50 mJ, up to 70 mJ). The mean number of treatment sessions per patient was 4.5 and 6.8 for full-and mini-NAFL, respectively, and the mean time interval between each treatment session was 8.7 weeks (2.9–60.6 weeks). After “full” and “mini” NAFL treatment, 23.1% and 0% of the patients had 1%–24% improvement, 7.7% and 13.3% had 25%–49% improvement, 15.4% and 40% had 50%–74% improvement, and 53.8% and 46.7% had 75%–100% improvement, respectively. Their study demonstrated that six “mini” treatments were equivalent to three “full” treatments in reducing acne scars. Notably, adverse event rates were significantly lower in the “mini” NAFL group, compared with the “full” NAFL group (6.0% vs. 18.2% for PIH and 14.8% vs. 33.3% for erythema, respectively). In our study, 73.91% of the patients showed 26%–50% improvement in acne scarring and 26.09% of the patients showed 1%–25% improvement in acne scarring on the 1550-nm NAFL side. Compared with the previous studies, our result demonstrated inferior efficacy; this may be due to the fewer treatment sessions and lower treatment coverage. With the use of 755-nm picosecond laser with DLA, only one patient had acne-induced postinflammatory erythema (PIE); he showed excellent improvement at 3-month follow-up after three sessions. Our findings regarding the efficacy of 755 nm-picosecond lasers with DLA for PIE are consistent with those of Zhang et al.,[7] which suggest that this therapy is effective and safe in this condition [Figure 3]f.

PIH is one of the most common complications of procedures performed using laser and other light sources in patients with dark skin phenotype (III to VI).[15] A consensus on the use of an Erbium-doped 1550-nm fractionated laser suggests that the treatment settings for acne scars depend on the skin type. For skin types I to III, the suggested settings are 30–70 mJ of energy, TL of 7–11, and 8–12 passes. For skin types IV to V, the suggested settings are 30–70 mJ of energy, TL of 4–5, and eight passes.[16] The higher TL (of 7) used in our patient with skin type IV could account for the occurrence of PIH on the 1550-nm NAFL side. Therefore, TLs should be increased with caution in darker skin phenotypes. In this regard, in a split-face comparison study, Cheyasak et al.[17] have shown that a short-term application of topical corticosteroids (clobetasol propionate ointment) after ablative fractional resurfacing is associated with a decreased risk of PIH in Asian patients. Corticosteroids can induce anti-inflammatory proteins and prevent the formation of potent inflammatory mediators. In the cited study, no significant difference in scar improvement or acneiform eruption rates was observed. In our study, the incidence of PIH on Asian skin (4.35% and 0% for 1550-nm NAFL and 755-nm picosecond laser with DLA, respectively) was lower than that of the studies conducted by Chan et al.[14] and Huang et al.[18] The application of topical corticosteroids immediately after the treatment could explain the low PIH rates, especially since the rate of prolonged erythema (78.26%) in our study was higher than that observed in the study conducted by Chan et al.[14]

Acne-prone patients were more likely to experience posttreatment acne, presumably due to the disruption of follicular units during treatment and re-epithelialization. The use of oral antibiotics (e.g. 100 mg doxycycline twice daily) during subsequent treatments can prevent future outbreaks in these patients.[10] In this study, two patients suffered acneiform eruption on the 3rd day after the first treatment on the 1550-nm NAFL side. Both had not taken doxycycline as prescribed, and the acneiform eruption resolved after they continued oral doxycycline for 5–7 days.

Brauer et al.[19] treated patients (skin types I to V) with facial acne scarring using a 755-nm picosecond laser with DLA (spot size, 6 mm; fluence, 0.71 J/cm2; repetition rate, 5 Hz; pulse width, 750 ps; and a mean of 3037 pulses) at 4-to 8-week intervals for six treatment sessions. A 25%–50% global improvement was observed on masked assessment. The mean pain score was 2.83/10. Patients experienced transient facial erythema and mild edema, but no exfoliation, vesiculation, crusting, scarring, hypopigmentation, or PIH. In another retrospective study, 42 Asian patients (skin types III to IV) with facial atrophic acne scars were treated using a 755-nm picosecond laser with DLA (spot size, 6 mm; fluence, 0.71 J/cm2; repetition rate, 10 Hz; pulse width, 750 ps; and a mean of 2500 pulses) at 2- to 6-6lse intervals. All patients exhibited a >25% improvement after an average of 4.28 sessions; the eight patients who underwent six treatment sessions showed a >50% improvement. The PIH risk was 4.7% (2/42, both spontaneously resolved).[18] In a study by Zhang et al.,[7] 20 Chinese patients with acne scars were treated with a 755-nm picosecond laser with DLA (spot size, 6 mm; fluence, 0.71 J/cm2; repetition rate, 5 Hz; pulse width, 750 ps; and 5 passes) at 4- to 6-6sse intervals for 3 sessions. The échelle d'évaluation clinique des cicatrices d'acné score showed a 28% improvement and the mean pain score was 3.20 ± 0.50 (scale of 0–10). The adverse effects included mild erythema, edema, and scabbing. Given the fewer treatment sessions, our study demonstrated a 1%–25% improvement in all patients. Our findings regarding adverse effects such as transient erythema and pain were consistent with those of previous studies.[7],[18],[19] The disruption of the dermo-epidermal junction by the 1550-nm NAFL could have resulted in a higher PIH risk than with the 755-nm picosecond laser with DLA. In terms of safety, 755-nm picosecond laser with DLA for acne scar treatment was superior to 1550-nm NAFL [Figure 1]e, [Figure 2]d, [Figure 3]e.


  Conclusions Top


The 1550-nm NAFL showed superior efficacy than the 755-nm picosecond laser with DLA for atrophic facial acne scar in Asian patients. Due to the minimal posttreatment complications, the 755-nm picosecond laser with DLA may be the best choice for those who request “little to no down-time” treatments. To reduce the risk of PIH, a short-term application of topical corticosteroids should be considered. Overall, the 755-nm picosecond laser with DLA seems a safe alternative for patients with type IV skin.

Financial support and sponsorship

This work was supported by the Xiamen Science and Technology Benefiting Project Fund under Grant (3502Z20184012).

Conflicts of interest

Prof. Wen-Hung Chung, an editorial board member at Dermatologica Sinica, had no role in the peer review process of or decision to publish this article. The other authors declared no conflicts of interest in writing this paper.



 
  References Top

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Tanghetti EA. The histology of skin treated with a picosecond alexandrite laser and a fractional lens array. Lasers Surg Med 2016;48:646-52.  Back to cited text no. 4
    
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Finney R, Torbeck R, Saedi N. Non-ablative fractional resurfacing in the treatment of scar contracture. Lasers Surg Med 2016;48:170-3.  Back to cited text no. 5
    
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Haimovic A, Brauer JA, Cindy Bae YS, Geronemus RG. Safety of a picosecond laser with diffractive lens array (DLA) in the treatment of Fitzpatrick skin types IV to VI: A retrospective review. J Am Acad Dermatol 2016;74:931-6.  Back to cited text no. 6
    
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Zachary CB, Kelly KM. Laser and other energy-based technologies. In: Bolognia JL, Schaffer JV, Cerroni L, editors. Dermatology. 4th ed. Philadelphia (PA): Elsevier Saunders; 2018. p. 2376-80.  Back to cited text no. 8
    
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Chayavichitsilp P, Limtong P, Triyangkulsri K, Pratumchart N. Comparison of fractional neodymium-doped yttrium aluminum garnet (Nd: YAG) 1064-nm picosecond laser and fractional 1550-nm erbium fiber laser in facial acne scar treatment. Lasers Med Sci 2020;35:695-700.  Back to cited text no. 9
    
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Graber EM, Tanzi EL, Alster TS. Side effects and complications of fractional laser photothermolysis: Experience with 961 treatments. Dermatol Surg 2008;34:301-5.  Back to cited text no. 10
    
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Modena DA, Miranda AC, Grecco C, Liebano RE, Cordeiro RC, Guidi RM. Efficacy, safety, and guidelines of application of the fractional ablative laser erbium YAG 2940 nm and non-ablative laser erbium glass in rejuvenation, skin spots, and acne in different skin phototypes: A systematic review. Lasers Med Sci 2020;35:1877-88.  Back to cited text no. 11
    
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Huang CH, Hsieh FS, Chang HC, Peng JH, Peng HP. 755 nm picosecond laser for facial atrophic scar-Case reports of long-term clinical efficacy following up. J Cosmet Dermatol 2019;18:778-82.  Back to cited text no. 12
    
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Chrastil B, Glaich AS, Goldberg LH, Friedman PM. Second-generation 1,550-nm fractional photothermolysis for the treatment of acne scars. Dermatol Surg 2008;34:1327-32.  Back to cited text no. 13
    
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Chan NP, Ho SG, Yeung CK, Shek SY, Chan HH. The use of non-ablative fractional resurfacing in Asian acne scar patients. Lasers Surg Med 2010;42:710-5.  Back to cited text no. 14
    
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Sherling M, Friedman PM, Adrian R, Burns AJ, Conn H, Fitzpatrick R, et al. Consensus recommendations on the use of an erbium-doped 1,550-nm fractionated laser and its applications in dermatologic laser surgery. Dermatol Surg 2010;36:461-9.  Back to cited text no. 16
    
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Cheyasak N, Manuskiatti W, Maneeprasopchoke P, Wanitphakdeedecha R. Topical corticosteroids minimise the risk of postinflammatory hyper-pigmentation after ablative fractional CO2 laser resurfacing in Asians. Acta Derm Venereol 2015;95:201-5.  Back to cited text no. 17
    
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