Putative photoacoustic damage in skin induced by pulsed ArF excimer laser.

Argon-fluoride excimer laser ablation of guinea pig stratum corneum causes deeper tissue damage than expected for thermal or photochemical mechanisms, suggesting that photoacoustic waves have a role in tissue damage. Laser irradiation (193 nm, 14-ns pulse) at two different radiant exposures, 62 and 156 mJ/cm2 per pulse, was used to ablate the 15-microns-thick stratum corneum of the skin. Light and electron microscopy of immediate biopsies demonstrated damage to fibroblasts as deep as 88 and 220 microns, respectively, below the ablation site. These depths are far in excess of the optical penetration depth of 193-nm light (1/e depth = 1.5 micron). The damage is unlikely to be due to a photochemical mechanism because (a) the photons will not penetrate to these depths, (b) it is a long distance for toxic photoproducts to diffuse, and (c) damage is proportional to laser pulse intensity and not the total dose that accumulates in the residual tissue; therefore, reciprocity does not hold. Damage due to a thermal mechanism is not expected because there is not sufficient energy deposited in the tissue to cause significant heating at such depths. The damage is most likely due to a photoacoustic mechanism because (a) photoacoustic waves can propagate deep into tissue, (b) the depth of damage increases with increasing laser pulse intensity rather than with increasing total residual energy, and (c) the effects are immediate. These effects should be considered in the evaluation of short pulse, high peak power laser-tissue interactions.

Low-energy, Q-switched ruby laser iridotomies in Macaca mulatta.

Laser iridotomies have been pursued as a means of performing anterior segments surgery as a virtually noninvasive procedure. An ideal single laser pulse technique has been elusive. In this study, iridotomies in rhesus monkeys were produced with a single exposure to a Q-switched ruby laser pulse. The iridotomy formation was accompanied by acoustic wave generation, bubble formation, and explosive tissue disruption, evidence of a nonlinear laser-iris interaction. The average energies at which these iridotomies were produced ranged between 18 and 48 mJ, some of the lowest energies reported for a laser iridotomy. Corneal changes were observed both at the epithelium and at the endothelium in some, but not all, of the eyes exposed. The epithelial changes morphologically resembled nonlinear damage reported for transparent solids. Damage to physical materials has been attributed to stimulated Brillouin scattering, a mechanism that may also play a role at the cornea. Consideration of such phenomena should be a part of the clinical evaluation prior to exposure of a cornea to high-power laser pulses. Although the endothelial change was more difficult to analyze, a shock-wave effect could not be discounted.

Argon laser trabeculotomies in primates: evaluation by histological and perfusion studies.

The continuous argon laser beam has been applied to the trabeculum at the anterior chamber angle of one eye of nine primates. The treatment was evaluated by light and scanning electron microscopy and constant rate infusion studies at different intervals following the laser treatment. This histological studies revealed coagulative necrosis, with trabeculotomies extending into Schlemm's canal in the immediate postoperative period. However, complete closure of the laser-induced trabeculotomies by healing was observed within 1 to 3 weeks following the treatment. Outflow facility data as measured by the perfusion studies revealed somewhat increased values of the treated eye during the early 2 weeks after laser treatment. On longer follow-up, no significant outflow differences were measured between the treated and untreated eyes.

Retinal vessel photocoagulation: a quantitative comparison of argon and krypton laser.

Retinal arteries of owl monkeys were photocoagulated with single exposures to argon laser green light (514 nm), krypton laser green light (531 nm), and krypton laser yellow light (568 nm). The distribution of damage along the vessel in different retinal layers was characterized geometrically after serial sectioning of the histopathologic material. Krypton laser radiation (green and, to an even greater extent, yellow) produced measurably greater effects on retinal vessels and adjacent structures than on deeper retinal levels; argon laser radiation (green) produced greater effects on the pigment epithelium. Krypton yellow produced the greatest total effect. The location of damage to the retinal arteries and pigment epithelium differed, with the peak of the damage around the arteries being farther from the optic disc than was the peak of the pigment epithelial damage.

Laser photocoagulation with biomicroscopic scleral indentation.

The treatment of peripheral retinal tears by laser photocoagulation is an accepted technique. One of its limitations is its difficulty in use near the ora serrata. The inability to treat the anterior border of a rentinal tear may allow the tear to progress to clinical retinal detachment despite treatment of the tear's posterior and lateral borders. The use of a scleral indentation funnel at the time of laser photocoagulation permits the sealing of all margins of the break. This technique increases the number of retinal tears that can be treated by the laser, and it may improve the rate of success of photocoagulation of peripheral retinal tears.

Indentation laser photocoagulation of peripheral retinal neovascularization.

The treatment of peripheral retinal neovascularization by laser photocoagulation is an accepted technique. One of its limitations is the difficulty in photocoagulating retinal neovascularization that has become even slightly elevated from the underlying pigment epithelium. The failure to close the neovascular frond and the production of a vitreous hemorrhage are the complications from the direct photocoagulation of elevated neovascularization. The currently accepted method of treating the feeding retinal arteriole and venule, although successful, requires multiple treatment sessions. The use of a scleral indentation funnel at the time of laser photocoagulation permits the direct photocoagulation of elevated neovascularization in some cases. This technique increases the number of neovascular fronds that are amenable to direct laser photocoagulation, improves the rate of success of closure of the neovascularization by photocoagulation, decreases the necessary number of treatment sessions, and decreases the risks from treatment.

Argon endolaser.

We developed an endolaser probe that is capable of delivering argon laser light for photocoagulation of retinal breaks or vascular fronds. Energy is transmitted through a fiberoptic cord from a console outside of the surgical area to an endolaser probe inside the operating suite. The probe can be fired into fluid- or gas-filled media. With the use of this system, panretinal photocoagulation can be performed rapidly and conveniently during a vitrectomy procedure. We have also successfully managed posterior retinal tears and bleeding fibrovascular fronds with this system.

Variation of energy density in argon laser photocoagulation.

The power density at the retina provided by presently available laser photocoagulators is subject to variation. Three factors contribute to making the retinal image of the laser beam substantially different from the spot size indicated on the selector of the photocoagulator. These are the operator's variable accommodation, the astigmatism introduced by the contact lens, and the depth of focus of the observation system. The assumption that the same setting on the instrument regularly produces the same power density at the retina will lead to errors in comparing lesions. The safest procedure is to start from the threshold in every location.

Internal ophthalmoplegia after argon laser panretinal photocoagulation.

Internal ophthalmoplegia was found in eight eyes of four patients with juvenile-onset diabetes. All eight eyes had received argon laser panretinal photocoagulation (PRP) for proliferative diabetic retinopathy. Internal ophthalmoplegia was not found in any of the 14 eyes of seven patients with juvenile diabetes who had not had photocoagulation treatment. This group included one patient in whom internal ophthalmoplegia was present after treatment. Laser injury to the short ciliary nerves, as they course anteriorly on the inner surface of the sclera, is the probable cause of internal ophthalmoplegia in these patients. To my knowledge, this complication has not been reported previously, but it appears to be a common side effect of PRP.

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.

Argon laser photocoagulation treatment of iris cysts following penetrating keratoplasty.

Two patients with iris cysts were successfully treated with argon laser photocoagulation. There was no evidence of recurrence of the cysts 51/2 and four years after treatment. To our knowledge, these cases represent the first reported cases of iris cysts following keratoplasty treated with argon laser photocoagulation that have documented long-term follow-up.

Argon laser photocoagulation for senile macular degeneration. Results of a randomized clinical trial.

The Senile Macular Degeneration Study (SMDS) is a multicenter controlled clinical trial designed to answer the question, "Is argon laser photocoagulation useful in preventing severe visual loss in eyes with evidence of senile macular degeneration and a choroidal neovascular membrane outside the fovea?" Eligible patients were assigned randomly to a "treatment" group or a "no treatment" group. Recruitment in the SMDS has been terminated because, after 18 months of follow-up, 60% of untreated eyes v 25% of treated eyes had experienced severe visual loss. Follow-up of all patients continues to assess long-term results of treatment. Patients with senile macular degeneration who are at risk for the development of choroidal neovascularization should be examined periodically so that if symptomatic neovascularization develops, treatment can be considered before irreversible visual loss occurs.

Dual delivery system for argon laser photocoagulation. Improved techniques of the binocular indirect argon laser photocoagulator.

A dual delivery system provided alternate delivery of the laser beam to the slit lamp and binocular ophthalmoscope. Ophthalmologists may choose between the two systems in accordance with the nature and location of the fundus lesion. A pilot study comparing the rate of laser hit between the slit-lamp photocoagulator and the binocular indirect argon laser photocoagulator (BIALP) showed that accuracy was better with the slit lamp and BIALP when they were operated in the sitting position than with the BIALP operated in the standing position. A photo-electric safety switch was attached to the blocking filter of the BIALP to protect operator's and patient's eyes. The improved machine and techniques increased the efficiency and safety of argon laser photocoagulation. Postoperative use of the BIALP was of particular value. Laser photocoagulation in children's eyes became possible for the first time with the BIALP.

Laser iridotomy for aphakic pupillary block.

In six patients with aphakic pupillary block, argon laser produced full-thickness iridotomies that succeeded in restoring anterior chamber and intraocular pressure to normal. In one case, it was shown that location of iridotomy is important in determining whether or not iridotomy will succeed in relieving aphakic pupillary block. In two cases, pupillary block had resulted in shallowing of the anterior chamber without pressure elevation. Cases reported here show that continuous laser energy, such as from an argon laser, can produce a full-thickness opening, in contrast to the short duration pulse of the ruby, which will destroy only pigmented structures without producing a full-thickness iris opening. This need to produce some degree of spread of damage to unpigmented tissue elements in order to achieve and iris opening is a problem in phakic patients where injury to the lens must be avoided.

Iris photocoagulation therapy of aphakic pupillary block.

Five patients who underwent uneventful cataract extraction developed flat anterior chamber (AC) secondary to pupillary block, 2 1/2 to 4 weeks postoperatively. None had a wound leak. After drug therapy had failed to restore the AC, iris photocoagulation was performed. Four eyes were treated with a xenon-arc photocoagulator, and one with both a portable xenon-arc unit and an argon laser. The AC deepened immediately and permanently in all cases. No complications occurred, and visual acuity was good. Iris photocoagulation with a xenon-arc unit is a valid alternative to intraocular surgery in therapy for flat AC that is caused by aphakic pupillary block in patients in whom medicinal therapy fails and no wound leak is present.

Anterior chamber depth alteration after retinal photocoagulation.

Anterior chamber shallowing is a syndrome that may occur after retinal photocoagulation for diabetic retinopathy. Angle closure glaucoma may occur. Peripheral iridectomy is not indicated, as the condition is self-limited and will resolve with or without medical therapy within a few days. A vascular occlusive phenomenon leading to congestion in the choroidal system is postulated as the cause of this phenomenon. The ciliary body may be shifted anteriorly and rotated inwardly to produce the anterior chamber changes observed.

Comparison of krypton and argon laser photocoagulation. Results of stimulated clinical treatment of primate retina.

We compared the clinical and histological effects of argon blue-green laser (ABGL), argon green laser (AGL), and krypton red laser (KRL) photocoagulation on the primate retina. Burns were produced in juxtafoveal and papillomacular bundle and in nonmacular areas in a manner simulating treatment of a choroidal neovascular membrane (NVM). In the juxtafoveal and papillomacular bundle areas, ABGL photocoagulation caused extensive inner retinal damage while KRL photocoagulation spared inner retinal structures. The effects of AGL photocoagulation in the fovea were intermediate in extent between KRL and ABGL photocoagulation. Axonal transport studies also showed differential effects of these wavelengths on retinal ganglion cell function. Nonmacular effects were similar for all three modalities. These results suggest that the krypton red wavelength may be more suitable than the argon green or argon blue-green wavelengths in treating choroidal NVMs near the fovea.

Repair of small blood vessels with the neodymium-YAG laser: a preliminary report.

A technique for repair of incisions in small blood vessels (diameter, 0.3 to 1.0 mm) in the rat is described using a Neodymium-YAG laser. It is possible to seal the incision without the use of sutures and to preserve the lumen of the vessel. The advantages of this technique over electrocoagulation and microsuture techniques are pointed out. Although the work is in preliminary stages, the technique is considered to be relatively safe, and the potential use of the application in human surgery is indicated. The possible complications of this technique are pointed out.

Regeneration of cervical epithelium after laser vaporization.

The process of reepithelialization after laser vaporization of normal cervical squamous epithelium was examined using light and electron microscopy. Tissue specimens were obtained from seven patients at time intervals ranging from seven to 16 days after laser vaporization. Immature squamous epithelium appeared at the edge of the laser crater between seven and 14 days, and by 14 to 16 days, the immature epithelium covered the entire crater area. The observations made in this study concur with those of other studies of the healing process of squamous epithelium, whereby immature cells from the surrounding undamaged epithelium migrate into the damaged area, eventually differentiating into a full thickness of epithelium.

Direct, indirect, and sham laser photocoagulation in the management of central serous chorioretinopathy.

The role of argon laser photocoagulation in the management of central serous choriorectinopathy was evaluated in a prospective randomized study of eyes with leaks smaller than 250 microns in diameter in the early frames of the angiogram. Eyes were assigned to Group A when the leak was located in the papillomacular bundle or within 500 microns of the capillary-free zone and to Group B when the leakage site was located outside the papillomacular bundle and more than 500 microns from the capillary-free zone. Thirty eyes in Group A underwent either a sham argon laser treatment or a real argon laser treatment directed to the pigment epithelium under the elevated retina at a site remote from the site of fluorescein dye leakage (indirect laser photocoagulation). Twelve eyes in Group B underwent either a laser treatment directed to the site of fluorescein dye leakage (direct laser photocoagulation) or indirect laser photocoagulation. Compared with indirect photocoagulation, direct laser photocoagulation shortened the duration of central serous chorioretinopathy by approximately two months, a statistically significant difference. When compared to sham treatment, indirect photocoagulation did not significantly alter the duration of central serous chorioretinopathy. During an 18-month interval, the recurrence rate in the eyes treated with sham and indirect laser photocoagulation was 34%, whereas no recurrences were observed in the eyes treated with direct photocoagulation. There were no complications from photocoagulation in any of the eyes.