Experimental retinal and ciliary body photocoagulation using a new 670-nm diode laser.

PURPOSE: Evaluation of ocular tissue reactions to 670-nm diode laser. METHODS: Twelve eyes of 12 pigmented rabbits were used. Transscleral contact laser delivery of a new 670-nm diode laser was used to produce retinal laser lesions in four rabbits; endolaser application of this laser produced photocoagulation of the retina in another four rabbits; and ciliary body lesions were produced by transscleral application of this laser in a third group of four rabbits. The rabbits were killed either 2 days or 1, 3, or 6 weeks later; lesions were evaluated by gross examination and histology. RESULTS: The mildest visible retinal lesions were produced by transscleral contact application at 0.2 J (2 seconds, 100 mW); explosive lesions began at 0.6 J. The mildest visible lesions were produced by endolaser application at 50 mW (spot size, 0.5 mm); intensive reactions started to occur at 300 mW, but no explosive lesions were produced below 600 mW. With contact transscleral application, substantial ciliary body reactions occurred at 0.5 and 1.0 J. Histologic examination disclosed destruction of the outer retina, pigment epithelium, and parts of the choroid in mild lesions, and of all retinal layers in the intense lesions. CONCLUSIONS: In this experimental study, the 670-nm diode laser appears to be a promising modality for laser photocoagulation of the retina and ciliary body.

Biodegradable self-reinforced polyglycolic acid spiral stent in prevention of postoperative urinary retention after visual laser ablation of the prostate-laser prostatectomy.

PURPOSE: The efficacy and safety of a new biodegradable (self-reinforced polyglycolic acid) spiral stent in securing free voiding despite edema after visual laser ablation of the prostate were studied. MATERIALS AND METHODS: A biodegradable spiral stent was inserted into the prostatic urethra in 22 patients immediately after visual laser ablation of the prostate. Uroflowmetry, measurement of residual urine volume, urine culture, cystoscopy and assessment of symptomatic improvement were done before, and 1, 3 and 6 months after visual laser ablation of the prostate. RESULTS: All 22 patients voided freely on day 1 or 2 after visual laser ablation of the prostate. However, 4 patients later had urinary retention due to a short spiral or too rapid spiral degradation. Half of the patients experienced a transient decrease in flow with some obstructive symptoms at 3 weeks that lasted 1 to 2 weeks. At 4 weeks all spirals were degraded and 3 patients had a positive urine culture. The maximum flow rate increased and the residual urine volume decreased significantly concomitantly with significant symptomatic improvement. CONCLUSIONS: The self-reinforced polyglycolic acid spiral stent can effectively and safely prevent postoperative urinary retention after visual laser ablation of the prostate.

Energy levels needed for cyclophotocoagulation: a comparison of transscleral contact cw-YAG and krypton lasers in the rabbit eye.

The energy levels needed for cyclophotocoagulation using either transscleral contact krypton or cw-YAG lasers were compared in pigmented rabbits. The same transscleral laser probe was used for both lasers. With the krypton laser, 0.25 J of energy caused macroscopically detectable lesions, and 1.5 J led to widespread destruction of the ciliary body. With the cw-YAG laser, the first detectable lesions were produced at 0.5 J. Similarly, at higher energies, twice as much energy was required using the cw-YAG as compared with using the krypton laser to produce comparable lesions. Histologically, lesions of the same macroscopic severity made with the two lasers were similar. We conclude that the transscleral contact krypton laser is an efficient instrument for cyclophotocoagulation. Although these results may not be directly applied to human eyes, it appears that the poorer scleral transmission of the krypton beam is offset by its higher level of absorption in the pigmented epithelium of the ciliary body.

Thermal effects in tissues from combined simultaneous coaxial CO2 and Nd:YAG laser beams.

This study examines the depth of thermal coagulation and charring in swine liver, kidney cortex, tongue (inferior surface), skeletal muscle, inflated lung, and skin resulting from in vivo incision with simultaneous coaxial CO2 and Nd:YAG (1.064 microM) laser beams. At values of 20 w and 40 w, respectively, and at values of 30 w and 60 w, respectively, of combined CO2 and Nd:YAG laser radiation, coagulation depths determined histologically in liver were significantly greater (P less than 0.01) than in the other tissues and were significantly less in inflated lung (P less than 0.05) than in other tissues for the larger laser power settings employed. Coagulation depths achieved at 10 w and 20 w, respectively, and at 20 w and 40 w, respectively, of CO2 and Nd:YAG laser power were comparable to those obtained by other workers in liver and other relatively vascular tissues using a contact Nd:YAG laser tip. Charring depths obtained at power settings of 30 w (CO2) and 60 w (Nd:YAG) were greater in liver (P less than 0.001) than in all other tissues examined. Hemostasis during incision was achieved only for values of the ratio of CO2 to Nd:YAG laser power in the range 2-3 in the more vascular tissues, liver and kidney cortex, whereas hemostasis was achieved also in the lesser vascular tissues at higher values. These results strongly suggest the usefulness of combined simultaneous CO2 and Nd:YAG laser beams in surgery of the more vascular organs and tissues.

Irradiation of human dental tissues with CO2-, Nd:YAG-, and CO2-Nd:YAG combination laser.

Extracted third molars were used to study the effect of Nd:YAG laser irradiation combined with CO2 laser beam on dental hard tissues. The specimens were studied with SEM after lasing and the size of the impact areas and beam penetration into enamel and dentin were planimetrically analyzed. High-energy CO2 laser (e.g. 10 s irradiation with 10 W output energy) penetrated all enamel and dentin. The simultaneous addition of Nd:YAG irradiation to the CO2 beam was found to increase the effect of CO2 laser, while Nd:YAG irradiation alone, used with equivalent energy densities, did not cause any effect on enamel surface. Thus, Nd:YAG laser was found to potentiate statistically significantly the effect of CO2 irradiation, but the morphologic alterations on dental hard tissues, such as crater formation at the beam focus site, appeared to be due to CO2 irradiation alone.

Transcleral contact krypton-laser photocoagulation of the retina in rabbits.

Transcleral contact retinal krypton laser photocoagulation of the retina was studied in rabbit eyes. The laser application was performed under indirect ophthalmoscope visual control with indentation of the sclera by the laser probe. Retinal lesions were produced with powers ranging from 0.2 to 0.3 W and application times between 1 and 2 sec. The lesions were studied histologically 2, 5, 10, 12, 20, 30 and 70 days after treatment. Histopathological examination of the lesions showed damage of mainly the outer retinal layers in light lesions, and to all layers of the retina in the more intense lesions. No scleral damage was observed in the light lesions, whereas transient oedema of the inner sclera was seen in the intense lesions. Studies with enucleated rabbit eyes showed that indentation of the sclera by the laser probe substantially decreased the power needed to produce a retinal lesion. It is concluded, that when used with scleral indentation, transscleral krypton laser photocoagulation of the retina can be performed with minimal damage to the sclera.

Lasers in medicine.

Since its discovery, the laser has been intensively investigated and used in medicine, first in ophthalmology then in ear, nose and throat surgery, gynaecology, neurosurgery etc. Development spans from the ruby and argon lasers in outpatient eye surgery to the carbon dioxide and Nd:YAG lasers in the operating theatres and further on to the PDT-dye lasers, excimer and solid state angioplasty lasers or flash lamp pumped "gallstone cracker" lasers. The CO2-Nd: YAG laser combination will be described as the state-of-art surgical laser. This simultaneous, coaxial and coherent combination laser offers a new possibility to cut and coagulate effectively at the same time. Operating times are shortened and bleeding volumes minimised. The CO2-Nd: YAG laser represents a new type of interaction between laser and tissue, laser enhanced tissue absorption, which will be described.

Effects of XeCl excimer laser on the eyelid and anterior segment structures.

We evaluated the in vitro and in vivo effects of an XeCl excimer laser on the eyelid and anterior segments of the eye. The wavelength of this laser was successfully transmitted through a quartz fiberoptic system. The action of the XeCl excimer laser through our system was more photocoagulative than photoablative.

Comparison of the effects of argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers on ocular structures.

We evaluated the effects of argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers on ocular structures. We produced corneal incisions, optical iridotomy, capsulotomy, and retinotomy with these lasers. Incisions produced with ArF showed sharply defined borders with minimal coagulative effects to the adjacent structures. Cuts created with KrF showed coagulative necrosis of the wound edges ranging from two to five um in width. From our study it appears that ArF has photoablative action and KrF has a predominantly photoablative action with minimal photocoagulative effect on the tissue.

A neodymium-YAG endolaser.

We used a CW-YAG endolaser to photocoagulate the fundus of the rabbit and monkey. We varied the power settings, exposure durations, and probe-retina distances to establish the parameters for threshold and bursting (choroidal hemorrhage) lesions. We found that the amount of energy needed to create a retinal lesion increased proportionally with the distance between the probe and the retina. To produce a choroidal hemorrhage at a given distance required at least four times the power required for a threshold coagulative lesion at the same distance. We also found that we could achieve a strong choroidal reaction without hemorrhage by using the coagulative threshold parameters of power and distance with an increased exposure time. Photocoagulation of the retina using the CW-YAG depended on the presence of melanin.