Low-energy linear-incision neodymium: YAG laser iridotomy versus linear-incision argon laser iridotomy. A prospective clinical investigation

When the Q-switched neodymium: YAG (Nd: YAG) laser is focused through the Wise 103-diopter (D) iridotomy-sphincterotomy lens (103-D lens) at low energy levels, the peripheral iris fibers can be cut individually across the iris tension lines to produce large iridotomies of controllable size. Thirty patients had linear-incision Nd:YAG laser iridotomy in one eye and linear-incision argon laser iridotomy in the other. Two-hour post-laser IOP rises averaged 7.33 mmHg for the Nd:YAG laser and 8.64 mmHg for the argon laser. The argon laser produced lens burns in 9 of 30 eyes, including 7 of 9 blue eyes. No lens damage occurred with the Nd:YAG laser. No corneal or retinal damage was seen with either laser. Local oozing of blood inhibited optical breakdown and required a pause before completion in 5 of 30 eyes with Nd:YAG iridotomy, including 4 of 6 dark brown thick irides. Because the iris fibers must be cut by direct contact with the laser plasma, serial cutting of iris fibers by multiple low-energy plasmas is safer than a single-shot, high-power plasma occupying the full thickness of the iris. Because it is effective and because it avoids the hazards of argon laser iridotomy and of high-power Nd:YAG laser iridotomy, linear incision Nd:YAG laser iridotomy is recommended as the safest method of iridotomy.     

Treatment of lipid keratopathy with the argon laser.

Twenty-two patients with lipid keratopathy were treated with argon laser photocoagulation to the feeder vessels. Two were grafted just over a week after treatment and the corneal discs examined histologically. The remainder of the patients were followed up for a least a year. In 6 cases the visual acuity improved, in 3 deteriorated, and in 10 did not change. The density and extent of the lipid deposition were diminished in 50% of cases. The commonest complications were bleeding into the lipid keratopathy and iris damage. The only serious problem was a disciform type of lipid keratopathy that flared up after treatment. Suggestions are made on improvements in the technique of laser application.     

Shock-wave effect on anterior segment structures following experimental neodymium:YAG laser iridectomy

The short-pulse laser may prove superior to the argon laser in producing noninvasive iridectomies. Little is known of the effects of the laser shock-wave on anterior segment structures adjacent to the iris. To investigate this question, iridectomies were produced in two owl monkeys using a neodymium (Nd):YAG laser and tissues were evaluated by light microscopy and scanning and transmission electron microscopy. For purposes of comparison, one eye received an iridectomy produced by an argon laser. Results indicate that while clean iris colobomas can be produced with a well-focused Nd:YAG laser, its shock-wave affects tissues in both the trabecular meshwork and corneal endothelium if the iridectomy is located within 0.8 mm of the limbus. No damage to the trabecular meshwork or corneal endothelium was evident after the argon laser iridectomy.     

The effect of combined application of argon and Nd-YAG lasers on iridectomy in rabbits

Recently iridectomy using an argon or Nd-YAG laser to treat narrow angle glaucoma has become popular, and is now the procedure of choice over the standard surgical technique. However, the shock wave of the Nd-YAG laser causes hemorrhage in almost all cases and the high energy level of the Nd-YAG laser, which is required for iridectomy, causes injury to the lens and cornea. Furthermore, there is a tendency toward closure of the iridectomy site after argon laser application. We performed iridectomies by a combined application of argon and Nd-YAG lasers in pigmented rabbits to improve iris bleeding, iridectomy patency, and lens and corneal damage. The iridectomy patency and the lens and corneal damage were examined with a scanning electron microscope. The rabbits that underwent laser iridectomies with only the Nd-YAG laser were used as a control group. Based on the results, it can be concluded that laser iridectomy by a combined application of argon and Nd-YAG lasers results in a lower rate of bleeding, a higher rate of patency, and less damage to the lens and cornea as compared with iridectomy performed by Nd-YAG laser only.     

Phthalocyanine photodynamic therapy of experimental iris neovascularization.

Photodynamic therapy using chloroaluminum sulfonated phthalocyanine (CASPc) effectively closed experimental iris neovascularization induced in 6 eyes of cynomolgus monkeys by argon laser retinal vein occlusion. Neovascularization was followed by iris photography, fluorescein angiography, and histopathologic examination by light and electron microscopy. Intravenous injection of CASPc followed by irradiation with 675 nm light damaged endothelial cells and pericytes, leading to exposure of the basal lamina and thrombotic occlusion of the blood vessels. Surrounding tissue appeared preserved without evidence of thermal damage. Resorption of occluded vessels by macrophages began 2 to 3 days after photodynamic therapy. Neovascularization reappeared 7 days after photodynamic therapy, probably representing growth of new vessels. Photodynamic therapy with CASPc may be a useful adjunct in the treatment of iris neovascularization. The model is useful in elucidating the ultrastructural changes observed after photodynamic therapy using phthalocyanines.     

Photodynamic therapy with verteporfin in a rabbit model of corneal neovascularization

PURPOSE: To determine the efficacy of photodynamic therapy (PDT) with verteporfin (Visudyne; Novartis AG, Basel, Switzerland) for treatment of corneal neovascularization in a rabbit eye model. METHODS: Corneal neovascularization was induced in Dutch belted rabbits by placing an intrastromal silk suture near the limbus. Verteporfin was administered by intravenous injection at a dose of 1.5 mg/kg, and the pharmacokinetics of verteporfin distribution in the anterior segment or PDT-induced (laser energy levels 17, 50, and 150 J/cm(2)) regression of corneal blood vessels were then determined. To assess PDT-induced toxicity of the anterior segment, corneal and iris/ciliary body histology, and IOP were evaluated after PDT. RESULTS: Verteporfin accumulation in vascularized regions of the cornea and the iris/ciliary body tissue were time dependent and maximum levels achieved at 60 minutes after injection. In rabbits, PDT of corneal vessels using laser energy of 17 or 50 J/cm(2) resulted in 30% to 50% regression of corneal neovascularization; however, in these animals, a rapid regrowth of new blood vessels occurred between 3 and 5 days. In the rabbits receiving PDT using laser energies of 150 J/cm(2), the mean vessel regression was 56%. During the nine days of the laser therapy follow-up period, no vessel regrowth was observed in these rabbits. Histologic examination of the anterior segment after PDT (150 J/cm(2)) showed localized degeneration of the corneal blood vessels without observable change in other anterior segment structures. CONCLUSIONS: These results provide evidence that PDT can produce significant regression of neovascular corneal vessels with no observable toxicity to the anterior segments. However, the optimal laser energy necessary to induce long-term regression (150 J/cm(2)) was three times that used to treat choroidal neovascularization.     

显微内窥镜下超全视网膜光凝治疗虹膜新生血管探讨

目的 探讨眼显微内窥镜在玻璃体切除术后虹膜新生血管超全视网膜光凝中的作用.方法 回顾16例16只眼玻璃体切除术后虹膜新生血管在内窥镜下行超全视网膜光凝的临床资料.选择玻璃体切除术后,术中行部分视网膜光凝.病因为糖尿病视网膜病变8只眼、视网膜中央静脉阻塞6只眼、视网膜血管炎2只眼;10眼人工晶体眼、6只眼无晶体眼,瞳孔难以散大;2只眼眼压高,14只眼正常;虹膜新生血管Ⅰ期14只眼、Ⅱ期2只眼.三腔内窥镜进入眼内进行视网膜超全光凝.对比观察虹膜新生血管消退情况、眼压、视力变化及并发症出现,随访3月至3年.结果 15眼1次超全视网膜光凝术后3个月虹膜新生血管消退,1眼继发新生血管性青光眼,眼压术后恢复正常,视力治疗前后无明显变化,未见虹膜损伤、视网膜脱离、眼内炎等手术并发症.结论 超全视网膜光凝是治疗虹膜新生血管的有效手段.玻璃体切除术后人工晶体或无晶体眼瞳孔难以散大情况下,显微内窥镜下的眼内视网膜光凝是可靠选择,可作为眼外视网膜光凝的有力补充.     

Corneal transmissibility of diode versus argon lasers and their photothermal effects on the cornea and iris

Purpose : Diode laser (810 nm) may possess theoretical advantages over the argon blue‐green laser (488 nm) for iridotomy/iridoplasty in an eye with oedematous cornea, such as the acute angle‐closure glaucoma (AACG) patient, because of better diode laser tissue penetration in opaque media. We assessed the transmissibility of diode and argon lasers through corneas of varying clarity and evaluated the histopathological features of cornea and iris burns produced by these lasers. Methods : The transmission of diode and argon lasers through human donor corneal buttons of three grades of clarity – clear, intermediate, and hazy – were compared. Corneal buttons of these varying levels of clarity were also treated with argon and diode lasers, with the beams deliberately focused onto the mid‐stroma to assess their photothermal effects. Exposed pigmented irides from whole human eyes were treated directly with argon and diode lasers. The lasers were delivered via slit‐lamp systems and the energy settings used were 1000 mW for argon and 980 mW for diode; spot sizes for both lasers were 100 μm, with exposure durations of 0.1 s. Light microscopy studies of these tissues were performed. Results : Transmissibility of diode laser in clear, intermediate, and hazy corneas were 89, 87 and 85% respectively and was significantly superior to argon laser (78, 73 and 70% respectively; P < 0.001, paired Student’s t‐test). Diode laser did not produce morphological changes in all three grades of corneas whereas argon‐laser‐treated hazy corneas showed photothermal damage. Both lasers produced deep iris burns, with the diode laser tending to produce deeper burns. Conclusion : Our findings suggest that diode laser may be the ideal laser for iridotomy/iridoplasty in the AACG patient with hazy cornea.     

Argon laser treatment of lipid keratopathy.

Sixty-three cases of vascularised lipid keratopathy were treated with the argon laser to occlude feeder vessels which had been identified by fluorescein angiography. There was a reduction in extent in 62% and density in 49%. Visual acuity was improved in 48%. Six patients had keratoplasties shortly after treatment, none of which showed graft rejection. Minor complications included temporary haemorrhage into the cornea and iris atrophy. A more serious problem was severe corneal thinning after resorption of lipid. The patients had to be carefully followed up and maintained on a low dose of topical steroid.     

Successful argon laser photocoagulation of diffuse epithelial ingrowth following concomitant persistent pupillary membrane removal and phacoemulsification

A 57-year-old woman had concomitant surgery of persistent pupillary membrane removal and uneventful phacoemulsification through the same temporal clear corneal incision in her left eye. Short axial lengths (right eye, 21.08 mm; left eye, 20.39 mm) with shallow angles were noted bilaterally, and other findings were not remarkable. The patient experienced angle-closure attacks 3 and 7 months postoperatively. At the second angle-closure attack, diffuse epithelial ingrowth was observed. The epithelial ingrowth covered the intraocular lens surface in the interpupillary area, the iris surface surrounding the pupil, and the temporal anterior chamber angle, but did not reach the corneal endothelial incision. After observation of iris blanching with laser photocoagulation, argon laser photocoagulation was applied to the epithelium covering the iris and angle 7 times during the following month. The epithelial ingrowth was completely removed and did not recur during the 36-month follow-up. Financial disclosure: No author has a financial or proprietary interest in any material or method mentioned.     

Effects of Argon Laser Iridotomy on the Corneal Endothelium of Pigmented Rabbit Eyes

Purpose

In Asian countries, laser iridotomy for the treatment of angle-closure glaucoma is a common cause of bullous keratopathy, which may be associated with a shallow anterior chamber and dark iris pigmentation in Asians. Several cases of corneal decompensation after argon laser iridotomy have been reported. In the present study, we evaluated the harmful effects of argon laser iridotomy on the corneal endothelium.

Methods

Argon laser iridotomy was performed on the right eyes of pigmented rabbits. Changes in corneal thickness and endothelial cell density after laser iridotomy were evaluated. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was performed for assessment of corneal endothelial cell apoptosis. Combined staining with alizarin red and trypan blue, as well as a live/dead cell assay, were performed for evaluation of damage to the corneal endothelium induced by laser iridotomy.

Results

Corneal thickness did not change immediately after laser iridotomy; however, a significant increase was observed 24 hours after iridotomy (p = 0.001). The endothelial cell density of laser-treated eyes four days after laser iridotomy was significantly decreased compared with control eyes (p < 0.001). TUNEL staining showed many TUNEL-positive cells in the corneal endothelium and corneal stroma. No endothelial trypan blue-stained cell nuclei were observed after laser iridotomy; however, several large endothelial cells with damaged membrane integrity were observed. The live/dead cell assay clearly showed a large number of dead cells stained red in several areas throughout the entire corneal button 24 hours after iridotomy.

Conclusions

Argon laser iridotomy induces corneal endothelial cell apoptosis in pigmented rabbit eyes, resulting in decreased endothelial cell density.     

Cooling Prevents Induction of Corneal Damage by Argon Laser Peripheral Iridotomy

Purpose

There are many reports of corneal complications caused by argon laser peripheral iridotomy. In this study, we investigated whether cooling the anterior ocular segment during laser iridotomy prevented corneal damage.

Methods

A space for cooling the anterior ocular segment by perfusion with ice-cold water was made between the cornea and a contact lens. Dutch pigmented rabbits were excessively irradiated by an argon green laser, aiming at the peripheral iris. We used a contact lens without a cooling system as a control. Temperature in the anterior chamber and intraocular pressure were also monitored throughout the experiment.

Results

During laser treatment, the temperature without the cooling system rose to a maximum of 44.5°C in the anterior chamber, whereas use of the cooling system consistently kept this temperature at 11.1°–16.1°C. Although most eyes treated without cooling showed corneal damage, damage was seen in only a few or in no eyes cooled during laser treatment.

Conclusions

Argon laser treatment using contact lenses with a cooling system drastically reduced the corneal damage induced by argon laser peripheral iridotomy. This technique may be acceptable for clinical use, considering its technical simplicity and low incidence of treatment-related complications.?Jpn J Ophthalmol 2007;51:317–324 © Japanese Ophthalmological Society 2007

     

超全视网膜光凝治疗虹膜新生血管

目的了解光凝治疗虹膜新生血管的疗效及其激光治疗时的参数。方法回顾总结15例出现虹膜新生血管接受氩离子激光超全视网膜光凝治疗患者的术后虹膜新生血管消退情况和眼底激光治疗参数。结果11眼(73.3%)完成超全视网膜光凝,术后3月虹膜新生血管完全消退,视力无显著下降。结论早期诊断和及时、充分、有效的眼底激光光凝治疗,能有效地促使虹膜新生血管消退,阻止病变进展。     

Laser iridectomy. A controlled study comparing argon and neodymium: YAG

Laser peripheral iridectomies were performed on both eyes of 38 patients with acute or chronic primary angle-closure glaucoma or with narrow angles capable of closure. The right eye was treated with the neodymium YAG laser (Nd:YAG) and the left eye with the argon laser. Patients were followed for a minimum of eight months. The mean number of applications to produce iris penetration was six with the Nd:YAG laser and 73 with the argon laser. Visual acuity, postoperative intraocular pressure (IOP), corneal changes, and pigment dispersion were similar in the two groups. Microhyphema was more prevalent in the Nd:YAG iridectomy group. Pupillary distortion, iritis, and late failure of patency were more frequent in the argon laser group. Nd:YAG laser iridectomies require fewer applications and produce less inflammation. This controlled study demonstrates that when properly and carefully performed, the Nd:YAG laser is at least as effective and appears to be as safe as the argon laser for performing peripheral iridectomies.     

Proliferation of the vascular endothelium of the iris following total debridement of the corneal epithelium and limbal excision of rabbits

BACKGROUND: Damage to the corneal epithelium causes not only a reaction for its repair but also affects other parts of the cornea as well as different components of the anterior segment of the eye. The purpose of this investigation was to analyze the consequences, following epithelial and limbal damage, to the iris of rabbits (Oryctolagus cuniculus). METHODS: The corneal epithelium was thoroughly scraped followed by surgical excision of the limbus. Next, (3)H-thymidine ((3)H-TdR) was injected intravitreally both into the right (experimental) and left (control) eyes which had their anterior segments processed for autoradiography at intervals of 2, 7 and 21 days after surgery (three rabbits per interval). The irises were also examined with scanning-electron and confocal microscopy after Evans blue injection. RESULTS: There was a high frequency of labeling in the cells of the iris blood vessels in the experimental eye, particularly the endothelial ones. The ratio of labeled cells between experimental and control irises was 40:1, with a population of nuclei increasing by 25% and remaining labeled up to 21 days. There was also an increase in the volume of the iris vasculature as shown by confocal microscopy. The high labeling frequencies of the vascular cells were observed throughout the iris from the ciliary to the pupillary regions. CONCLUSIONS: The lesions on the corneal epithelium elicit proliferation of the iris vascular cells, mainly its endothelium, as well as an early breakdown of the blood-aqueous barrier. The daughter cells resulting from the damage to the eye surface were detected up to 21 days after a single injection of (3)H-TdR, most likely due to their slow turnover. As a consequence of this proliferation, the vasculature of the iris increased in volume.     

Accumulation of photosensitizer ATX-S10 (Na) in experimental corneal neovascularization

PURPOSE: To determine the most appropriate time for laser irradiation to produce selective occlusion of new corneal vessels by photodynamic therapy (PDT) with a new photosensitizer, ATX-S10(Na). METHODS: The time course of the plasma levels of ATX-S10(Na) and the degree of dye accumulation in the corneal neovascularization after intravenous administration was determined in rabbit eyes. Plasma concentration of ATX-S10(Na) was analyzed by a spectrophotometer. The amount of ATX-S10(Na) in the new corneal vessels was measured by nitrogen-pulsed laser spectrofluorometry. Frozen sections of neovascularized cornea and iris were observed by fluorescence microscopy. RESULTS: Plasma ATX-S10(Na) concentration was highest 5 minutes after dye injection and rapidly decreased and reached almost zero at 24 hours, indicating its prompt excretion from the body. The amount of ATX-S10(Na) in the new corneal vessels as measured by nitrogen-pulsed laser spectrofluorometry increased and reached maximal level at 2 to 4 hours. Under fluorescence microscopy, the dye was more abundantly localized in the wall of new corneal vessels than in the normal tissue at 2 to 4 hours. CONCLUSION: These results indicate that laser irradiation between 2 and 4 hours after dye injection is appropriate for selective PDT with ATX-S10(Na) for the occlusion of new corneal vessels.     

光动力学疗法治疗角膜新生血管后角膜的光电镜改变

目的观察应用国产光敏剂行光动力学疗法(PDT)治疗角膜新生血管后角膜的组织学改变。方法碱烧伤有色兔角膜制作角膜新生血管模型。血啉单醚5mg/kg自耳缘静脉注射,不同的能量密度61.2-52.8J/cm2的氲绿激光照射角膜新生血管根部,不注射血啉单醚并单纯行同等能量密度的激光照射组作为对照组,PDT治疗后3h、1周、1个月行角膜光电镜检查。结果PDT后3h可见角膜急性炎症反应,有大量中性粒细胞浸润和少量嗜酸性白细胞浸润,虹膜组织无损伤。PDT后1周角膜炎症反应大部分消失,可见新生血管腔内有无定形物质填塞和许多影子血管。透射电镜显示:PDT组角膜新生血管内皮细胞内线粒体显示出空泡样变,细胞形态不完整。结论血啉单醚作为光敏剂,应用氩绿激光对角膜新生血管行PDT治疗,导致新生血管内皮细胞损伤,能有效封闭角膜新生血管,对周围组织无明显损伤。     

Laser treatment to large iris cyst secondary to trabeculectomy

CASE REPORT: We report a case of postoperative large iris cyst secondary to trabeculectomy treated with Nd:YAG laser iridocystotomy. The patient was subsequently free of discomfort or significant inflammation. COMMENTS: This case suggests that large iris cysts may produce corneal decompensation. Laser treatment can collapse the iris cyst without other ocular tissue damage.