Nd:YAG Laser

Laser peripheral iridotomy and iridoplasty

Robert Ritch , Clement C.Y. Tham , in Ophthalmic Surgery: Principles and Practice (Fourth Edition), 2012

Neodymium:YAG laser peripheral iridotomy

The Nd:YAG laser creates a plasma of free ions and electrons at the site of optical breakdown. This photodisruption releases shock waves that mechanically cause tissue rupture, as opposed to the thermal effect of the argon laser 12 . Iris color and density are much less important than with argon LPI.

Suggested settings for Nd:YAG LPI have varied from one to four pulses per burst and from 1 to 10 mJ per burst. One should begin with a single pulse at approximately 1.5–3 mJ to assess the response of both the patient and the iris to the laser application. An increase in laser energy to 4–6 mJ is often sufficient to create a patent iridotomy with one to three additional applications. We prefer a linear incision technique using lower power burns, of the order of 1 mJ. We also prefer a single pulse per burst. It is very important to focus on the anterior iris stroma to maximize photodisruption and to minimize the possibility of lens injury. Portable Nd:YAG systems may facilitate iridotomy in debilitated patients or in remote areas 13 .

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Laser therapy in ophthalmology

J. Pašta , in Lasers for Medical Applications, 2013

Anterior capsulotomy

Photodisruptive Nd:YAG lasers were used in the 1980s to carry out anterior capsulotomy. A high pulse level was used to create a circular gap in the anterior capsule of the cataractous lens prior to cataract surgery. Further techniques such as extracapsular extraction and open chamber cataract surgery were also used. The technique of circular curvilinear capsulorhexis (CCC – circular tearing of anterior lens capsule with gentle forceps) was not yet developed, so it was necessary to employ a laser pre-treatment that created circular penetration into the anterior lens capsule. To open the anterior lens capsule, 200–300 laser breakdowns, each with 5–10  mJ energy, were needed. This treatment aggregated a huge amount of energy, and freeing lens massae debridement in the anterior chamber could quickly lead to complications such as increases in intraocular pressure, generation of inflammation or clouding of the anterior chamber. Therefore, surgery needed to be completed as soon as possible after pre-treatment. Because of the complications arising from the use of Nd:YAG lasers for this procedure, femtosecond photodisruptive lasers are currently used for intraoperative anterior capsulotomy (i.e. Yb:KYW, Yb-doped Potassium Yttrium Tungstate, laser wavelength 1030   nm). Optical cutting of the anterior eye segment with optical coherence tomography is carried out intraoperatively. The parameters are input into a femtosecond laser and a CCC is created (Fig. 13.26, 13.27).

13.26. Schema of circular curvilinear capsulotomy cut out by femtosecond laser.

13.27. Circular curvilinear capsulorhexis cut performed in vitro in a piece of PMMA by femtosecond laser as part of femtosecond laser assisted cataract surgery (FLAC) pattern.

If the capsule opening is small in diameter or occurs in conjunction with other eye diseases, the anterior capsule may shrink postoperatively by fibrosis. Nd:YAG photodisruptive laser radial anterior capsulotomy can be used to treat phimosis (excessive narrowing of anterior capsule opening), as this condition can reduce visual acuity or occlude the vision.

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Endoscopic Treatment of Bladder Tumors

Petrişor A. Geavlete , ... Bogdan Geavlete , in Endoscopic Diagnosis and Treatment in Urinary Bladder Pathology, 2016

4.24.2.3.1 Nd:YAG Laser

The Nd:YAG laser was the first type of laser used in urological practice. It uses a crystal of neodymium that produces a light invisible at a continuous wavelength of 1064 nm. Its reduced absorption by water and tissue determines an increased penetrability into the tissues, of 5–10 mm. Also, the Nd:YAG laser determines lesions by coagulation necrosis. In the acute phase, macroscopically the tissues appear ulcerated and covered by eschars. Microscopically, areas of necrosed tissue clearly delimited from the adjacent tissues are observed. After approximately 8 weeks, healing occurs with the appearance of an intense granulation tissue and a dense fibrosis ( Lopez-Beltran et al., 2002).

The increased penetrability of this type of laser determines an efficient coagulation, allowing transmural coagulation without perforating the bladder wall (Fig. 4.101). The disadvantage of this is the risk of injury to the adjacent organs, most frequently to the colon, without any existing bladder breaches (Ruiz-Tovar et al., 2008; Greskovich and von Eschenbach, 1991 ). This risk is higher in areas with a thin bladder wall, especially at the level of the dome. For this reason, it is recommended not to completely distend the bladder during the procedure. The incidence of this complication is described as 0.01% in the literature. This is why some authors recommend reducing the power of the laser to 30 W in patients who have suffered previous laser interventions on the bladder or in patients with tumors of the posterior bladder wall (Hofstetter, 1992).

Figure 4.101. Nd:YAG laser coagulation of a bladder tumor (a) observed by a whitening of the tissue (b–d).

The intervention is routinely performed using a power of 30–40 W, with the beam placed 3–4 mm from the lesions' surface. The energy is released in a continuous manner.

As coagulation of the tumor occurs it turns to a whitish color. Removal of the coagulated areas is required for the treatment of deep areas.

Treatment with this type of laser ensures a very good hemostasis, which makes postoperative bladder lavage to be rarely necessary.

The risk of bladder wall perforation and injury of the adjacent organs has limited the use of this type of laser.

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Cyclophotocoagulation

Roberto G. Carassa , in Ophthalmic Surgery: Principles and Practice (Fourth Edition), 2012

Trans-scleral application

The Nd:YAG laser (1064 nm) and the diode laser (810 nm) are both suitable for trans-scleral applications. Two trans-scleral approaches have been used in cycloablation: non-contact and contact. The diode laser has several advantages, including better absorption by melanin, good portability, and lower cost. Either continuous-wave or pulsed laser systems are available. Continuous-wave laser allows long and sustained energy delivery while a pulsed laser system transmits light energy at short pre-set time intervals. Trans-scleral photocoagulation is a 'blind' procedure because the ablative energy is directed toward an invisible target whose position can only be estimated from data obtained experimentally in human autopsy eyes. Exact beam focusing for NCTCP was thus suggested as being 1–1.5 mm posterior to the limbus 16, and the optimal location for the center of the probe in CTCP was 1.5–2 mm posterior to the corneo-limbal junction17. Localization of the ciliary body by transillumination should be performed in every eye before surgery. Ultrasound biomicroscopy can help to locate the exact ciliary body position (Fig. 45.2).

In NCTCP, laser energy is transmitted through the air from a slit-lamp delivery system. The procedure can be carried out using a pulsed Nd:YAG laser such as the Microruptor II, a continuous-wave model such as the Microruptor III (H.S. Meridian, Inc., Mason, OH), or a diode laser such as the DC3000 (Nidek, Inc., Palo Alto, CA), the Microlase (Keeler Instruments, Broomall, PA), or the Oculight SLX (Iris Medical, Mountain View, CA) (Fig. 45.3). The laser beam needs to be focused inside the ciliary body. This is done with the Nd:YAG laser by focusing the HeNe beam on the conjunctiva overlying the ciliary body and selecting the maximum offset18, thus providing a 3.6 mm posterior separation between the HeNe and the therapeutic beam and with the diode laser by defocusing the beam 1 mm toward the ciliary body. The Nd:YAG laser should be set at 4–8 J energy, while the diode laser should be set at 1500–2000 mW power output, 1 second time duration (thus producing 1.5–2 J spots), and 100–400 µm spot size (Table 45.1). The eye is kept in primary position because no significant differences were found between applying laser energy parallel to the visual axis and perpendicular to the sclera18. The beam is focused on the conjunctiva 1–2 mm behind the limbus. The distance is measured with a caliper and a marking pencil, or the slit beam of the biomicroscope. With the latter, the laser spots are placed in the middle of a 3 mm long slit beam, projected perpendicular to the limbus. Thirty to forty applications, evenly spaced over 360°, are placed in a single session, usually sparing the 3 o'clock and 9 o'clock positions to avoid damage to the long posterior ciliary nerves.

Using the diode laser, each spot should be defocused 1 mm toward the ciliary body. It is mandatory to keep a diagram of the treatment, specifically noting the laser settings used.

The contact technique has several advantages over the non-contact technique, which explains its wider clinical use. Reduced light backscattering and greater scleral transmission mean significantly less energy is needed. Arbitrary beam defocusing is avoided. The longer exposure time results in a predominantly coagulative necrosis of the ciliary processes as opposed to the blister formation found NCTCP. The use of specifically designed, hand-held probes improves precision by allowing easy spot location and by avoiding eye movement. The operation is done in the supine position so patients under general anesthesia can be easily treated. CTCP is carried out using either an Nd:YAG laser or a diode laser. The Nd:YAG lasers are the Microruptor III (H.S. Meridian, Inc., Mason, OH), and the Emerald (Crystal Focus, Viewpoint, Miami, FL; Fig. 45.4). The diode lasers are the Oculight SLX or the IQ810 (Iridex, Mountain View, CA; Fig. 45.5), and the DC-3000 (Nidek Inc., Palo Alto, CA). All systems are coupled with an optic fiber ending either in a sapphire probe (SLT, Microruptor III, Emerald), or in a specifically designed focusing bare quartz tip (Iridex G-Probe). These tips ensure less energy dispersion and easy positioning of their centers 1 to 1.5 mm posterior to the limbus, where the treatment is needed. The Oculight SLX and the IQ810 with their specifically designed G-Probe are the more widely used systems for CTCP.

The Nd:YAG laser is set at 4–7 W of power and 0.5–0.7 seconds duration while the diode laser is set at 1.75–2.6 W and 1.5–2.5 seconds (Table 45.2). The wide range in settings is partly related to the different lasers and, mostly, to the different sizes of the optic fiber used. The Oculight SLX and IQ810 are set at 1.8–2.0 W and 2 seconds duration. Considering the delicacy of the laser system and of the optic fibers and sapphire probes, a fiber transmission check is advisable in order to verify the total energy being delivered by the system19. The G-probe is intended to be used for just one treatment, even though different studies showed its safety for multiple use. The probe is placed in contact with the conjunctiva, positioning its center 1.2–1.5 mm posterior to the surgical limbus (Fig. 45.6). Particular care should be taken to keep the probe perpendicular to the scleral surface: an orientation as little as 15° off the perpendicular reduces the photocoagulative effect. A firm indentation is always needed in order to increase the energy transmission through the sclera and to avoid eye movement. The G-probe is specifically designed to facilitate its positioning. By placing the heel of its footplate adjacent to the limbus, the sapphire tip will be located 1.2 mm posterior to the limbus over the ciliary body and will have the correct angle on the scleral surface. Moreover, the laser tip, which protrudes 0.7 mm, is providing the required indentation (Fig. 45.7); 16–40 spots (Nd:YAG laser) or 16–20 spots (diode laser) are then applied over 360°, sparing the 3 o'clock and 9 o'clock positions in order to avoid damage to the long posterior ciliary nerves. In patients considered at high risk of hypotony, the treatment may be reduced to 180°. The energy must be adjusted in order to avoid audible 'pops' caused by tissue disruption secondary to overtreatment. The Oculight SLX and the IQ810 are initially set at 2 seconds and 1750 mW. The power is then increased in 250 mW increments to a maximum of 2500 mW until a pop is heard, then the power is decreased 250 mW.

After 1 to 4 weeks all eyes showing an inadequate response to the treatment should be re-treated. All parameters used for the initial treatment are maintained. Some surgeons prefer to deliver half as many spots. Multiple re-treatments can be done, although the risk of hypotony and phthisis increases. Some surgeons treat 180° and, if further treatments are necessary, apply additional 180° treatments, each time overlapping one quadrant previously lasered.

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Surgical Management

Philip A Bloom , ... Philippe Denis , in Glaucoma (Second Edition), 2015

Nd : YAG Cyclophotocoagulation

The Nd : YAG laser (1064 nm) with its longer wavelength has good scleral penetration (60–70%) and is used in the non-Q switched free-running thermal mode. In the noncontact laser, power settings of 4–8 J per application are used for a duration of 20 ms with 8–10 applications per quadrant. Treatment is usually applied from 270 to 360° and reduced for those at risk of hypotony and those with anticipated heavy ciliary body pigmentation. The laser beam is defocused so as to offset the focal point 3.6 mm into the eye when the helium–neon aiming beam is focused on the conjunctiva. A contact lens with markings can be used both to keep the lids open and also to blanch the conjunctiva and hence improve the laser delivery.

In the contact method the patient lies supine and a lid speculum is placed. The anterior edge of the 2.2 mm sapphire tip of the delivery fiberoptic hand piece is placed 0.5 to 1.0 mm from the limbus (the probe is centered 1.5–2.0 mm behind the limbus) and gentle pressure is applied with the probe, which is oriented perpendicular to the sclera. Power settings of 5–8 W with duration of up to 0.7 seconds are used. Eight to 10 spots are applied per quadrant to treat from 270 to 360°, with treatment adjusted for each individual patient.

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Tracheal Stenosis

Christopher R. Morse MD , ... Douglas J. Mathisen MD , in Medical Management of the Thoracic Surgery Patient, 2010

Bronchoscopic Approaches

▪

Nd:YAG laser photoresection:

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Although mostly employed for malignant upper airway lesions, laser treatment for benign tracheal stenosis has been reported in case series. 17–21

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Often reported in combination with gentle rigid bronchoscopic dilatation

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In general lesions should be short (i.e., <4 cm) with a visible endobronchial lumen. Simple weblike lesions are ideal.

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Indications include inoperable patients due to surgical considerations or significant comorbidities, patients who refuse surgical treatment, simple lesions such as postintubation granulation tissue that are easily and effectively handled by laser resection

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Note: Laser treatment is not the treatment of choice for tracheal stenosis

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Cryotherapy:

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Data for benign lesions are limited to several small case series only. 22, 23

KEY POINTS

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Often delay in diagnosis.

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Imaging important, but bronchoscopy is essential for diagnosis, and initial management.

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Significant experience necessary to determine whether lesion is amenable to surgical management, timing of surgical management, and for good outcomes.

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A comprehensive state of the art review on central airway obstruction has recently been published. 24

Brief Illustrative Case

•

History: 55-year-old woman with a 5-year history of progressive shortness of breath. Treated initially for adult-onset asthma with no relief of symptoms. Bronchoscopy revealed a subglottic stenosis 1.5 cm below vocal cords. No history of intubation, trauma, mediastinal mass, anti-neutrophil cytoplasmic antibody (ANCA) negative

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Examination: Vitals: HR, 60–70; BP, 120/68; respirations, 16/min; temp, 98.6o F, SPO2, 99% (room air). Physical exam unremarkable and patient breathing comfortably at rest.

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Imaging: Chest radiograph normal, Chest CT imaging normal. Tracheal tomograms demonstrate subglottic stenosis 1.5 cm below vocal cords

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Rigid Bronchoscopy: Normal vocal cords, tight subglottic stenosis (5–7 mm) with sufficient distance below vocal cords to allow for resection. Distal tracheobronchial tree normal.

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Management Idiopathic Tracheal Stenosis: Patient serially dilated in the operating room with rigid bronchoscopes. Through a collar incision, tracheal resection and reconstruction performed with resection of anterior cricoid. Postoperative course unremarkable and patient discharged on postoperative day 7 following repeat bronchoscopy.

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Photoacoustic Probes for In Vivo Imaging

Menglei Zha , ... Kai Li , in Methods in Enzymology, 2021

5.3 Photoacoustic imaging capability

The photothermal performance of BDT-TQ NPs denotes that these nanoparticles may hold great potential in PA imaging upon pulse laser irradiation. Herein, the photoacoustic imaging capability of nanoparticles is tested before they are used in biological applications. The PA signal intensity and photostability are the main factors that affect photoacoustic imaging capability of contrast agents. A custom-made acoustic-resolution photoacoustic computed tomography (PACT) system (Scheme 3) is designed for the evaluation the performance of BDT-TQ NP in PA imaging.

Scheme 3

Scheme 3. A custom-made acoustic-resolution photoacoustic computed tomography (PACT) system with the dual-modality ultrasound and photoacoustic imaging.

 Reproduced with permission from Zha, M., Lin, X., Ni, J. S., Li, Y., Zhang, Y., Zhang, X., et al. (2020). An ester-substituted semiconducting polymer with efficient nonradiative decay enhances NIR-II photoacoustic performance for monitoring of tumor growth. Angewandte Chemie International Edition, 59(51), 23268–23276. https://doi.org/10.1002/anie.202010228.

The PACT consists the Nd:YAG laser system, linear array transducer, and ultrasound system. The Nd:YAG laser system has an optical parametric oscillator (OPO) unit, and it can emit a 6–9  ns width laser pulse with pulse repetition rate of 20   Hz. The wavelength of the laser system is tuned between 400 and 2000   nm. To ensure that the surface of the animal model is uniformly illuminated, the fiber bundle is used to deliver the output light beam. The linear array transducer is used to capture the ultrasound (US) and PA (US/PA) data. After that, the data is digitalized via a research ultrasound system. The external trigger from the laser system is sent to synthesize the above data acquisition parts. Finally, the back-projection method restores the coregistered US/PA images. In order to ensure safety, the laser energy should be lower than the American National Standards Institute (ANSI) safety limit. Therefore, in this experiment, the laser energy is set to 10   mJ/cm2 at wavelengths of 808 and 1064   nm, which is lower than ANSI safety limit.

5.3.1 Equipment

1—Nd:YAG laser system (Quanta-Ray INDI-40-20, Spectra Physics, USA)

1—Linear array transducer (L11-4v, Verasonics, USA)

1—Research ultrasound system (Vantage 256, Verasonics, USA)

5—Capillaries

5.3.2 Reagents

BDT-TQP, BDT-TQT, BDT-TQE NPs (1   mg/mL)

1   × PBS

5.3.3 Procedure

1.

Dilute the BDT-TQ NP solutions to 0.25   mg/mL with 1   × PBS.

2.

Draw the BDT-TQ NP solutions with capillaries, respectively.

3.

Put the capillaries with liquid in the detection position, respectively.

4.

Record the PA spectra of BDT-TQ NPs (see Fig. 11A ) by using the PACT system, respectively. The laser energy set for PACT imaging is 2   mJ/cm2.

Fig. 11

Fig. 11. The photoacoustic imaging capability of BDT-TQ NPs. (A) PA spectra and (B) their relative PA intensity at NIR-I (808   nm) or NIR-II (1064   nm) wavelengths of BDT-TQ NPs (0.25   mg/mL).

 Reproduced with permission from Zha, M., Lin, X., Ni, J. S., Li, Y., Zhang, Y., Zhang, X., et al. (2020). An ester-substituted semiconducting polymer with efficient nonradiative decay enhances NIR-II photoacoustic performance for monitoring of tumor growth. Angewandte Chemie International Edition, 59(51), 23268–23276. https://doi.org/10.1002/anie.202010228.
5.

Relative PA intensity at NIR-I (808   nm) or NIR-II (1064   nm) wavelengths of BDT-TQ NPs is shown in Fig. 11B according the recorded PA spectra.

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Laser processing of medical devices

M.C. Sharp , in Biophotonics for Medical Applications, 2015

4.3.3 Other laser drilling processes

While pulsed Nd:YAG lasers are widely recognised for drilling, principally in metallic materials, other lasers are often used as well. CO 2 lasers can be used and can be particularly appropriate for polymers. Pulsed CO2 lasers can lack the pulse length or peak power when drilling metals, although high average power pulsed CO2 lasers can have high production rates for single-pulse 'on-the-fly' drilling (Olsen and Alting, 1995). An application related to 'on-the-fly' drilling is perforation of polymer films. This has become widely employed in the food packaging industry for atmosphere control packaging and to control package opening. Both of these applications are applicable to medical device packaging.

The pulsed Nd:YAG laser is good for drilling sub-millimetre holes in foils and thin sheets, but for applications that require larger numbers of smaller holes, such as the manufacture of mesh foils with individual holes of the order of 5–50   μm and a large open area, the DPSS laser can offer a better solution. The high repetition rates available (kHz) allow high productivity hole drilling (Tunna et al., 2006). Frequency doubling of DPSS lasers often provides better processing characteristics (Knowles et al., 2007; Karnakis et al., 2005). Frequency tripling and quadrupling into the UV allow these lasers to process polymers and other materials transparent to NIR and visible laser radiation (Ilie et al., 2007).

Excimer lasers are another important tool for small-hole drilling. The excimer laser is a pulsed laser that produces a large uniform beam that is mask imaged onto the workpiece and can produce arrays of holes, shaped holes and 3D structured holes (Rizvi et al., 2000).

Fibre lasers, both CW and nS pulsed fibre lasers, are also being introduced for laser drilling (Biffi and Previtalli, 2011).

Ultrafast lasers are also having an impact on laser drilling. Such lasers offer high beam quality, allowing for focal spot sizes down to less than 10   μm, especially when frequency doubled or tripled lasers are employed. More importantly, the ultrafast pulse lengths, typically <   20   pS, allow for material removal with virtually no heat effect on the substrate. Both solid state and fibre ultrafast lasers are available. The former tends to offer higher pulse energies (>   10   μJ to several mJ) and moderately high repetition rates (1–500   kHz), while pulse energies in fibre lasers are restricted typically to <   20   μJ but with repetition rates to 10's MHz. With many metals exhibiting ablation thresholds that require around 5   μJ for a spot size of the order of 25   μm, these lasers will machine and drill, but beam/workpiece manipulation at such high repetition rates is demanding.

Often the highest quality drilling occurs with pulse energies that are not greatly above that required to exceed the ablation threshold, and so many solid state lasers were run with low pulse energy or with beam attenuation to reduce the pulse energy where this could not be obtained directly from the laser. Reducing the pulse energy in this manner reduces average power and hence productivity. Recently, techniques have been developed that allow programmable splitting of a single laser beam, allowing up to at least 30 individual focal spots each machining and drilling at a high quality and using the full available average power of the laser (Kuang et al., 2008).

Another benefit of ultrafast laser drilling is that such lasers are often capable of machining polymers, ceramics and so forth, for which the base wavelengths (typically ~   775 or ~   1060   nm) are generally unsuitable for longer pulse lengths due to the lack of absorption.

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Laser Treatment of Leg Veins

Neil Sadick , Lian Sorhaindo , in Cutaneous and Cosmetic Laser Surgery, 2006

1064nm Nd:YAG

The long pulsed Nd:YAG laser system has undoubtedly become the treatment of choice for spider and feeding reticular veins. The versatility of this particular treatment definitely accentuates its present success possessing the ability to treat both red, superficial vessels and deeper blue vessels with simple adjustments in spot sizes, fluences, and pulse durations. In addition, this system – via its utility of a longer wavelength and subsequent epidermal bypass – increases the ability to treat darker skin phenotypes. Issues stemming from the hydrostatic pressure of feeder and reticular veins can also be addressed because veins up to 3 mm can be treated, although patient's tolerance to pain may become an issue as pain increases with treatment of larger vessels. For superficial vessels less than 1 mm in diameter, the optimal parameters include: small spot sizes of <2 mm, short pulse durations of 15–30 ms, and high fluences of 350–600J/cm 2. For reticular veins 1 to 4 mm in diameter, larger spot sizes (2–8 mm), longer pulse durations (30– 60 ms) and moderate fluences (100–370J/cm2) should yield successful results. As a result, the Nd:YAG laser has been embraced by many clinicians world wide as the state of the art for laser treatment of lower extremity vessels.

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Laser Skin Resurfacing: Ablative and Non-ablative

Tina S Alster MD , Elizabeth L Tanzi MD , in Surgery of the Skin, 2005

1320 nm Nd:YAG laser

A 1320 nm Nd:YAG laser was the first commercially available system marketed solely for the purpose of non-ablative laser skin remodeling. The 1320 nm wavelength is associated with a high scattering coefficient that allows for dispersion of laser irradiation throughout the dermis. The latest model is capable of delivering energy densities up to 24 J/cm 2 with a pulse duration of 350 μs through a 10-mm spot size hand-piece. The 1320 nm Nd:YAG laser hand-piece contains three portals: the laser beam itself, a thermal feedback sensor that registers skin surface temperature, and a dynamic cryogen spray apparatus used for epidermal cooling. When skin surface temperatures are maintained at 40–45 °C dermal temperatures reach 60–65 °C during laser irradiation, thereby effecting collagen contraction and neocollagenesis. In order to prevent unwanted sequelae (e.g. blistering) from excessive heat production, it is imperative that epidermal temperatures be kept lower than 50 °C. A series of three or more treatment sessions are scheduled at regular intervals (typically once a month) for maximum mitigation of fine rhytides. 73 Side effects of treatment are generally mild and include transient erythema and edema.

Menaker et al. 84 reported effective rhytide reduction in an early study using a prototype 1320 nm Nd:YAG laser. Ten patients with periocular rhytides received three consecutive laser treatments at bi-weekly intervals. Three 300 μs pulses were delivered at 100 Hz and fluence of 32 J/cm2 with a 5-mm spot size hand-piece. Epidermal protection was achieved with application of a 20 ms cooling spray after a 10 ms preset delay. Patients were evaluated at 1 and 3 months after treatment. Although four of the ten patients showed clinical improvement in rhytide severity by end-study, these findings were not statistically significant. Similarly, the slight homogenization of collagen noted on histology at 1 and 3 months following treatment was not statistically significant and inconsistent with the clinical findings.

In another study, Kelly et al. 85 treated 35 patients with mild, moderate, and severe rhytides using a 1320 nm Nd:YAG laser. Three treatments were delivered at 2-week intervals using fluences ranging 28–36 J/cm2 with a 5 mm spot size. Cryogen spray cooling was applied in 20–40 ms spurts with 10 ms delays. Patients were evaluated at 12 and 24 weeks following treatment with statistically significant improvement noted in all clinical grades after 12 weeks. Only the most severe rhytides; however, showed persistent improvement 24 weeks following treatment.

Goldberg devised two similar studies to examine the effectiveness of the 1320 nm Nd:YAG laser for the treatment of facial rhytides. In the first study, ten patients with skin types I–II and class I–II rhytides in the periorbital, perioral, and cheek areas were treated. 86 Four treatments were administered over a 16-week period using fluences of 28–38 J/cm2 with a 30% overlap and a 5 mm spot size. One or two laser passes were applied to achieve the treatment endpoint of mild erythema. Skin surface temperatures were limited to 40–48 °C using the aforementioned dynamic cooling spray in order to provide epidermal protection, whilst effecting dermal temperatures ranging 60–70 °C. Six months following treatment, two patients showed no clinical improvement, six showed 'some' improvement, and two showed 'substantial' improvement. This study emphasized several key points in non-ablative laser resurfacing. It suggested a thermal feedback sensor is best used intraoperatively with this technology in order for appropriate treatment fluences to be selected based upon the individual patient's cutaneous temperature, thereby maximizing dermal temperatures that effectively lead to collagen reformation. Furthermore, longer follow-up periods are usually required to fully appreciate the effect of serial treatment sessions on dermal collagen stimulation. In the second study, ten patients underwent full-face treatments with the 1320 nm Nd:YAG laser at 3–4-week intervals. 87 As with the first study, treatment results were inconsistent—four patients showed no improvement, four showed some improvement, and two showed substantial improvement in facial rhytides and overall skin tone.

Others also studied the 1320 nm Nd:YAG laser for treatment of facial rhytides in ten women. 88 Full-face treatment was administered to three patients, whereas two patients had periorbital treatment, and five patients received perioral treatment. Laser fluences of 30–35 J/cm2 were delivered in triple 300 μs pulses at a repetition rate of 100 Hz. Dynamic cryogen spray cooling was used with a 30 ms spurt and a 40 ms delay between cryogen spurt and laser irradiation. A thermal sensor was also used to maintain peak surface temperatures in the range of 42–45 °C in order to avoid excessive tissue heating. Treatments were administered twice a week over a period of 4 weeks, for a total of eight treatment sessions. Only two out of ten patients expressed satisfaction with their final result despite clinician evaluations showing significant improvement in five of ten patients and fair improvements in another three. Moreover, there was no correlation between histologic changes and the degree of subjective clinical improvement as judged by the patients.

A more recent study by Fatemi et al. 89 demonstrated that the 1320 nm Nd:YAG laser produced mild subclinical epidermal injury that could potentially lead to enhanced skin texture and new papillary collagen synthesis by stimulation of cytokines and other inflammatory mediators. Thus, the long-term histologic improvement seen in photodamaged skin may not be based solely on direct laser heating of collagen, but by further stimulation of cytokine release by heating the superficial vasculature. In addition, the histologic findings suggested that multiple passes with fluence and cooling adjusted to a Tmax of 45–48 °C can yield improved clinical results, as compared to those specimens in which epidermal temperatures above 45 °C were not achieved.

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