Determination of an appropriate laser setting for THC-YAG laser sclerostomy ab externo in rabbits.

To determine an appropriate setting for the THC-YAG laser (chromium-sensitized, thulium, and holmiumdoped YAG laser), we performed sclerostomy ab externo on 24 pigmented rabbits. The laser energy was delivered via a subconjunctivally-inserted fiberoptic probe that was placed at the limbus through a small conjunctival incision. We used four pulse-energy levels to perform the sclerostomies: 80 mJ, 120 mJ, 160 mJ, and 200 mJ. At all these levels, a new outflow pathway was easily created, a filtering bleb was formed, and intraocular pressure (IOP) was immediately reduced. Severe tissue damage around the sclerostomy site occurred with the 160-millijoule and 200-millijoule pulses. The 80-millijoule pulse created a relatively small patent sclerostomy, providing only relatively brief IOP reduction. We conclude that 120-millijoule is the most appropriate laser-pulse energy for use in pigmented rabbits.     

Ab-interno neodymium:YAG versus erbium:YAG laser sclerostomies in a rabbit model.

This study was undertaken to determine whether thermally-induced tissue necrosis was a factor in ab-interno contact-laser sclerostomy failure. A rabbit model was used to compare the continuous-wave Neodymium (Nd):YAG with the pulsed Erbium (Er):YAG laser with respect to such failure. Laser energy was focused into a fused-silica fiber optic (400 microns) for the Nd:YAG laser (12 W; 3 to 5 seconds), and into a single-crystal, uncladded sapphire fiber optic (250 microns) for the Er:YAG laser (7 to 8 mJ; 250 microseconds; 6 to 8 pulses). The Nd:YAG and Er:YAG lasers required from 21 to 35 J and from 42 to 64 mJ, respectively, to create the sclerostomies. Filtering blebs and intraocular pressure reduction lasted longer (log-rank test; P less than .03) and surgical complications were fewer in the Er:YAG group than in the Nd:YAG group. By creating sclerostomies with minimal thermal damage, the Er:YAG laser may offer significant clinical advantages over lasers producing larger thermal effects.     

Ab-interno erbium (Er):YAG laser sclerostomy with iridotomy in Dutch cross rabbits

An ab-interno technique using a pigmented rabbit model has been developed that uses a pulsed erbium:YAG laser to create an iridotomy with a sclerostomy through the same corneal incision. Laser energy was delivered with an articulated arm terminating in side-firing (850 or 650 μm OD) or end-firing (850 or 400 μm OD) fiber optic endoprobes, which allowed iridotomies and sclerostomies, respectively, to be created. Initially, sclerostomies (8–10, 8 mJ/300 μs pulses) and basal iridotomies (1–3, 4 mJ/200 μs pulses) were created with the larger probes. Problems encountered with this technique included corneal decompensation and rapid formation of peripheral anterior synechiae with occlusion of sclerostomies. The smaller endoprobes were then used to create midperipheral iridotomies and sclerostomies utilizing the same energy parameters. Sclerostomies created in this manner remained patent in the first postoperative week until the animals were sacrificed to obtain material for histologic study. © 1993 Wiley-Liss, Inc.     

THC:YAG laser sclerostomy: the resident experience.

Retrospective review of 14 consecutive THC:YAG laser sclerostomies done without the use of anti-metabolites revealed a uniform closure of the filtering bleb within 6 months of follow up. Also, the sclerostomy site was closed by iris or fibrous tissue. Based on these findings, I recommend that the present THC:YAG laser sclerostomy protocol be altered to allow for antimetabolite usage, prevention and treatment of iris prolapse, and control of intraocular inflammation.     

Internal sclerostomy with laser: a new approach to glaucoma surgery.

The creation of a fistula that permits controlled flow of aqueous from the anterior chamber to the subconjunctival space has been and remains the main technical goal of glaucoma filtering surgery. Currently, most complications are secondary to the surgical manipulation of the conjunctiva (mainly leakage from bleb and conjunctival fibrosis) or flattening of the anterior chamber. To overcome this problem, new methods are evolving in which the fistula is created from within the eye, with no conjunctival dissection. The performing of the sclerostomy by means of externally delivered laser energy is a further step in the same direction.     

Endometrial laser ablation in rabbits: a comparative study of three laser types

Endometrial laser ablation is one of the alternatives to hysterectomy in cases of intractable uterine bleeding. It is currently performed using the Nd:YAG laser at 1.06 microns. The aim of this study was to compare the tissue effect of three types of laser irradiation (Nd:YAG laser at 1.06 and 1.32 microns and holmium laser at 2.12 microns) on the rabbit endometrium. Crater formation, coagulation necrosis, and muscle necrosis were evaluated at the time of ablation, as well as at 1 week and 4 weeks postablation. The results were assessed by determining the depth and width of the affected portion in the uterine wall (lumen to serosa). It was shown that Nd:YAG laser at 1.32 microns caused more generalized and extended effects as compared with the other laser types examined. Endometrial regeneration was faster after ablation by the Nd:YAG laser at 1.06 microns and the holmium laser than by the Nd:YAG laser at 1.32 microns. The widest range of "ablation energy" (defined as that causing ablation without muscle damage) was achieved by applying the holmium laser. Further evaluation of the holmium laser for this indication is recommended.     

Application of pulsed and continuous wave 1.32 and 1.06 microns wavelengths of the Nd:YAG laser in the canine tracheobronchial tree: a comparative study

Previous investigations have shown good clinical potential for the use of the 1.32 microns wavelength Nd:YAG laser because its soft tissue absorption is better than that of the 1.06 microns wavelength Nd:YAG laser. The 1.32 microns wavelength Nd:YAG laser has an absorption coefficient in water that is 10 times higher than the 1.06 microns wavelength Nd:YAG laser. A comparative in vivo study of laser soft tissue effects was performed by using the 1.32 microns wavelength and the 1.06 microns wavelength Nd:YAG lasers in a pulsed wave (PW) mode and continuous wave (CW) mode using a non-contact endoscopic delivery system. A standard 5 mm mucosal lesion was made in the canine tracheobronchial tree down to the level of the perichondrium. Soft tissue and cartilage effects were examined by light and scanning electron microscopy, acutely, 1 week and 2 weeks after operation, and a comparison was made between the different laser modalities. To create similar lesions, higher energy was required when using the 1.06 microns wavelength Nd:YAG laser. Soft tissue injury was greater with the 1.06 microns wavelength in CW mode, and no cartilage damage occurred in the PW mode. Soft tissue and cartilage repair after 1 and 2 weeks was better with the 1.32 microns wavelength laser. In comparison, the CO2 laser and the contact Nd:YAG laser proved to be more precise cutting tools than the 1.32 microns wavelength or the 1.06 microns wavelength Nd:YAG lasers. Both Nd:YAG laser wavelengths were useful for coagulation and vaporization of tissues and blood vessels. More studies are needed to determine the effect of the new 1.32 microns wavelengths on endotracheal tumors.     

Ab interno and ab externo filtering operations by laser contact surgery

A new method to create filtering tracts ab interno or ab externo which may eventually prove useful in eyes with poorly controlled glaucoma is described. Fiberoptics of 200 microns diameter, with either cleaved or 500 microns ball lens tips, were coupled to the output of an argon gas laser emitting a number of radiation lines in the ultraviolet (333 to 363 nm) wavelengths. This system was used to perforate the corneoscleral limbal tissue of enucleated bovine eyes with a small number of laser applications to create a filtering fistula. Corneoscleral limbal perforation with a 200 microns cleaved fiber required 0.6 to 1.1 J total energy, delivered with a laser power of 0.5 W, or greater, for 0.1 second. With a 500 microns ball lens fiber tip a tract of nearly 0.5 mm diameter was created, requiring 5.1 to 10.4 J total energy, delivered with a laser power of 2.0 W, or greater, for at least 0.1 second. The energy required for perforation from the external surface to the anterior chamber was the same as the energy required for ab interno perforation.     

Optical principles related to optimizing sclerostomy procedures.

A simple probe, consisting of a 200-micrometer uncladded silica optical fiber, advanced from a protecting 22-gauge hypodermic needle, was used to create sclerostomy fistulas both ab interno and ab externo by means of a combined radiation/mechanical effect. Perforation was achieved by exerting gentle forward pressure on the fiber in synchrony with the delivery of radiation pulses. An irradiation protocol suitable for producing such canals in cadaver porcine eyes was delineated using Ho:YAG, Nd:YAG, and diode laser energy sources. Despite significant differences in the pulse energy required for perforation (0.25, 7, and 8 J for the Ho:YAG, diode, and Nd:YAG lasers, respectively), the extent of collateral damage was comparable for each type of laser. The physical mechanisms underlying these findings are discussed.     

New long-wavelength Nd:YAG laser at 1.44 micron: effect on brain

A wavelength-shifted Nd:YAG laser, tuned to coincide with the infrared absorption peak of water at 1.44 microns, was used to make lesions in normal rabbit brain. A total of 48 lesions were made with power up to 20 W, with energy up to 40 joules, and with two different spot sizes. These lesions were compared to lesions made with 1.06 microns radiation from an Nd:YAG laser under identical operating conditions. Measurements of blood-brain barrier damage and width, depth, and volume of tissue affected were obtained 30 minutes after placement of the lesions. It was found that 1.44-microns lesions produced photoevaporative tissue loss at the highest intensities used. The layer of coagulated tissue remaining after photovaporization had a mean thickness of 0.6 mm irrespective of the volume of tissue removed. There was no photovaporization in the 1.06-microns lesions. In addition, the amount of peripheral edema per unit volume of tissue coagulated was approximately half at the 1.44-microns wavelength. These findings suggest that the 1.44-microns Nd:YAG laser may be a useful surgical instrument since it combines the photoevaporative effect of the CO2 laser while maintaining the advantages of the conventional Nd:YAG laser (quartz fiber delivery and effective hemostasis).     

Laser sclerostomy ab interno using a continuous wave Nd:YAG laser

We report the use of a continuous wave Nd:YAG (CW-YAG) laser focused through a sapphire crystal to create a filtering bleb by ab-interno sclerostomy. A 2-mm clear corneal incision was made in each eye of five anesthetized Dutch Belted rabbits, and the 30-mm-long sapphire crystal with a 0.2-mm focal tip was passed across the anterior chamber until it came in contact with the opposite angle. Between two and three pulses of 0.8 J were required to produce a filtering bleb in each of the 10 eyes. The overlying conjunctiva was not damaged; the procedure time was under five minutes. Histological examination revealed a surrounding area of scleral melting that extended an average of 0.06 mm from the sclerostomy. These data suggest that the CW-YAG laser may be useful in performing glaucoma filtering surgery with minimal damage to surrounding ocular tissues.     

Silver oxide in YAG sclerostomy

YAG sclerostomy is a filtering procedure performed entirely with the neodymium:YAG laser through a goniolens as an alternative to trabeculectomy in the treatment of glaucoma. Extremely large pulse powers have been required in the past to complete the procedure. We found that an injection of silver-stabilized protein intrasclerally prior to the procedure makes it possible to perform the procedure with low total power.     

Percutaneous laser discectomy with the Ho:YAG laser.

A prototype Ho:YAG (2.15 microns) laser operating at 2-J/pulse, 3 Hz through a 600-microns fiber was employed to perform laser discectomies at the L3-4 disc through an 18G needle in five juvenile pigs. No temperature elevations were recorded in the posterior longitudinal ligament at the disc level and all animals recovered fully with no adverse sequelae, even immediately upon awakening from anesthesia. Pathologic examination demonstrated a wide swath of coagulation necrosis confined to the disc space. The Ho:YAG laser, owing to its close approximation to the intense 2.0 microns absorption band of water, appears to be a viable candidate for clinical trials of laser discectomy.     

Trans-scleral application of a semiconductor diode laser

We used a diode laser with an output power of 1 W through a fiberoptic light pipe (200 microns diameter) to deliver laser energy through the sclera of pigmented rabbits. Ciliary body destruction occurred with energy levels of 300-400 mW and exposure time of 0.5 sec. Retinal photocoagulation was achieved with energy levels of 200-500 mW in 0.5 sec. Histologic examination of acute lesions demonstrated thermal destruction of ciliary body processes and retina. Chorioretinal scar formation was observed clinically and histologically within 2-3 weeks. Our data indicate that the transscleral diode laser may be used for destruction of the ciliary body processes or peripheral retinal coagulation in pigmented eyes.     

Treatment of Facial Skin Using Combinations of CO2, Q-Switched Alexandrite, Flashlamp-Pumped Pulsed Dye, and Er:YAG Lasers in the Same Treatment Session

BACKGROUND: Many patients who seek facial CO2 laser resurfacing for improvement of photodamage are also concerned with "dark circles" under their eyes (periorbital hyperpigmentation) and/or telangiectasia as well as various types of deep scars on their faces. CO2 laser resurfacing alone provides limited improvement for these problems. OBJECTIVE: The purpose of this study was to demonstrate the conjunctive therapeutic effects of the CO2, Q-switched alexandrite, Er:YAG, and/or flashlamp-pumped pulsed dye lasers on facial skin treatments. METHOD: Thirty patients who underwent CO2 laser resurfacing were treated with additional lasers specific for their cosmetic concerns. Twenty patients with facial telangiectasias were treated with the pulsed dye laser immediately prior to CO2 laser resurfacing. Eleven patients with periorbital hyperpigmentation were treated with the Q-switched alexandrite laser immediately following use of the pulsed CO2 laser. Eight patients having sharply defined acne scars were treated with the Er:YAG laser following use of the CO2 laser. All patients had peripheral feathering performed with the Er:YAG laser. Nine patients were treated with all four lasers. RESULTS: In addition to significant improvement of the wrinkle scores from the CO2 laser resurfacing, patients had 75-100% clearing of the periorbital hyperpigmentation. All patients with facial telangiectasia showed virtually 100% improvement. All deep wrinkles and sharply defined scars responded with combined CO2/Er:YAG laser better than with CO2 laser resurfacing alone. All feathering was more uniform, with a more subtle transition to nontreated skin. There were no complications that could be attributed to the simultaneous use of multiple lasers. CONCLUSIONS: For patients who present with multiple cosmetic complaints, combined treatment using appropriate lasers offers excellent therapeutic outcome.     

Alternative lasers for endoscopic surgery: comparison of pulsed thulium-holmium-chromium:YAG with continuous-wave neodymium:YAG laser for ablation of colonic mucosa.

Precise and controllable tissue vaporization is essential for minimizing risk in removal of sessile polyps from the lumen of thin walled gastrointestinal organs such as the colon. We compared the ablative efficiency on canine colonic mucosa of the THC:YAG laser with the clinically employed cw Nd:YAG laser. Fresh canine colon was treated with a progressive dose schedule using each laser at several energy/power densities. Ablation depth was measured on fresh tissue and thermal (non-ablation or coagulative) damage examined histologically. The THC:YAG ablation rates were 13.7 +/- 0.8 and 10.2 +/- 0.4 microns/J at 55 and 85 J/cm2, respectively. The Nd:YAG laser generated 3.7 +/- 0.3, 2.8 +/- 0.1, and 3.6 +/- 0.2 microns/J at 4,460, 5,095, and 5,730 W/cm2, respectively. There was a significant (P less than 0.001) difference among the THC:YAG ablation rates and between the THC:YAG and Nd:YAG ablation rates (ANOVA). The THC:YAG laser craters had significantly less collateral thermal damage than Nd:YAG. The pulsed THC:YAG laser should have an important clinical role since its use could reduce the risk of perforation in endoscopic laser procedures such as the removal of sessile polyps.     

A new universal laser apparatus for intra and extraocular irradiation tasks in the eye

We describe a universal laser apparatus for multipurpose clinical tasks. The main unit consists essentially of a Haag-Streit slit lamp combined with a rigidly mounted Q-switched laser. The apparatus is designed basically for performing photodisruptive tasks. Radiation emitted by either a pseudocontinuous cw Nd:YAG laser (with a dynamic range of 10 W) or by an air-cooled 4-W argon ion laser energy source either may be transmitted via fiber optics into the main unit or, when detached from the main unit, may be used independently. Energy emitted by the modules and transported by specialized light cables and delivery systems can be used to perform transscleral Nd:YAG laser irradiation of the ciliary body or the choroid and retina. Probes are available for endocoagulation of the latter two by either cw Nd:YAG or argon laser light. Other probes are being developed for chorioretinotomy, internal sclerostomy, dissection of the sclera, or for other extrabulbar work. All functions are monitored and displayed by a central processor.     

Comparative investigations of the effects of the neodymium:YAG laser at 1.06 microns and 1.32 microns on tissue

The beneficial deep homogeneous coagulation of neodymium (Nd):YAG laser radiation at 1.06 microns owing to low absorption and high scattering in tissue has been documented widely. For another Nd:YAG laser wavelength at 1.32 microns the absorption coefficient of water and saline is approximately ten times higher than at 1.06 microns. This results in more efficient energy conversion into heat in tissue at 1.32 microns. The extinction coefficient in blood at 1.32 microns is only one-third of that at 1.06 microns. We would expect this to result in less heat dissipation by blood and deeper penetration in tissue at 1.32 microns. Nevertheless, at this wavelength scattering also contributes to an effective, uniform distribution of the laser light in the tissue. Animal experiments have been done to examine the effect of wavelength, irradiation time, and beam geometry on tissue damage and to assess its possible clinical uses. The results imply that the 1.32 microns wavelength will produce further indications for the use of the Nd:YAG laser in surgery.     

Trabeculectomy flap suture lysis with endolaser probe

Enhancing filtration after trabeculectomy with scleral flap sometimes requires cutting of the nylon suture. A new use of the endolaser probe to cut the nylon suture through hemorrhagic and edematous conjunctiva and Tenon's capsule is described. The probe compresses the tissue so that it is close to the suture for delivery of the laser energy. This application of the endolaser probe as an "ecto-laser" succeeded in enhancing filtration, raising the conjunctival bleb, and lowering intraocular pressure.     

Safety of high-energy neodymium:YAG laser pulses in YAG sclerostomy

YAG sclerostomy was performed in 15 eyes of nine cynomolgus monkeys. Individual pulse energies ranged between 10 and 135 millijoules. Total pulse energy ranged between 2,000 and 36,000 millijoules in order to test the extreme range of energy that might be required. Both acute effects and chronic effects were studied in the corneal endothelium, the lens capsule, the iris, the ciliary body, the retina, and the sclera. Techniques included flat preparations of the corneal endothelium, paraffin sections for light microscopy, and scanning and transmission electron microscopy. Our conclusion is that individual pulse energies of up to 135 millijoules with a total of up to 36 joules of energy are safe in monkey eyes when performing YAG sclerostomy.