Transscleral infrared laser for retinal ablation without retinal visualization in an experimental model

PURPOSE: To investigate whether transscleral diode laser can create retinal photocoagulation reliably without creating retinal holes under conditions simulating opaque media. METHODS: In New Zealand pigmented rabbits, optimal infrared diode laser power settings were determined, and transscleral retinal photocoagulation was then applied 4 mm and 6 mm from the limbus without retinal visualization. Transscleral testing was done using retina and cyclophotocoagulation probes placed directly on the sclera, on conjunctiva, and on silicone scleral buckles. RESULTS: A retina probe placed on the sclera achieved moderate retinal photocoagulation intensity in 75% of spots 4 mm from the limbus and in 50% of spots 6 mm from the limbus. Retinal holes were only formed when using the transscleral cyclophotocoagulation (TSCPC) probe. An association between burn intensity and the presence of conjunctiva was seen for the TSCPC probe (P = 0.0001) but not for the retina probe (P = 0.125). Photocoagulation spots did not exceed moderate intensity through any of the silicone scleral buckles tested. CONCLUSIONS: Transscleral infrared photocoagulation applied without retinal visualization did not cause retinal hole formation with a retina probe placed directly on conjunctiva, sclera, or scleral buckle material. A TSCPC probe created retinal holes when placed directly on sclera. A decrease in power was required for all treatments closer to the limbus.     

Experiments on the absorption of argon and krypton laser by blood

Experiments were performed to determine the absorption by and transmission through blood of argon blue-green (ABG) and green (AG) and krypton red (KR) laser light. Krypton was transmitted better through intact erythrocytes than argon. The difference between krypton and argon was greater if the erythrocytes contained oxygenated hemoglobin (Hb) than deoxygenated Hb. None of the wavelengths penetrated well a confluent blood specimen only 4 cells thick. Branch retinal vein occlusions were created in monkeys causing scattered areas of retinal hemorrhage. Argon burns placed in areas of retinal hemorrhage caused much inner or full thickness retinal damage. Krypton passed through the inner retinal hemorrhage without causing damage and created a burn at the level of the retinal pigment epithelium and inner choroid. Preretinal hemorrhages were created in rabbits by perforating Bruch's membrane with a high intensity krypton burn. Argon burns placed over the preretinal hemorrhages were absorbed much more than krypton burns. Neither argon or krypton however could penetrate even moderately thick preretinal hemorrhages to cause an underlying retinal burn.     

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.     

Clinicopathologic correlation of krypton red, argon blue-green, and argon green laser photocoagulation in the human fundus

One day before the scheduled enucleation for a choroidal melanoma, a patient agreed to have experimental laser burns placed in her fundus for the purpose of comparing the histopathologic effects of krypton red, argon green, and argon blue-green laser photocoagulation. When photocoagulation burns were applied to simulate treatment for a juxtafoveal choroidal neovascular membrane ( NVM ) there was relative inner retinal sparing with krypton red and transretinal effects with argon green. When treatment was applied outside the macula to simulate scatter or panretinal photocoagulation (PRP), there were no differences in histopathologic effect. This suggests that krypton red laser photocoagulation may be advantageous in treating juxtafoveal neovascular membranes, but is of no particular advantage when treating outside the macula.     

Altered uptake of infrared diode laser by retina after intravitreal indocyanine green dye and internal limiting membrane peeling

PURPOSE: To report an altered uptake and possible complication associated with the use of indocyanine green (ICG) dye, internal limiting membrane (ILM) peeling, and infrared diode laser. DESIGN: Interventional case report. METHODS: In two eyes (two patients) three-port pars plana vitrectomy was performed. Indocyanine green was injected into the vitreous cavity according to previously published protocol. The ILM was removed with a bent-tipped microvitreoretinal blade and ILM forceps. Photocoagulation was performed with an 810-nm infrared diode endolaser. RESULTS: Photocoagulation of the retina stained with ICG in areas with intact ILM produced more intense and superficial appearing retinal burns than photocoagulation where the ILM had been peeled. The retinal burns in areas of intact ILM stained with ICG also appeared more superficial than those typical of this laser when ICG is not used. CONCLUSIONS: Indocyanine green absorbs infrared laser light and produces a photothermal effect. Unwanted damage to the inner retinal layers may occur. Laser energy may also be prevented from reaching the deeper retinal layers, reducing the efficacy of treatment.     

高度近视患者LASIK术前预防性光凝的临床观察

目的 观察高度近视患者LASIK术前行预防性氩离子激光光凝的疗效。方法 LASIK术前对高度近视患者常规行直接眼底镜、三面镜和间接眼底镜配合巩膜压迫法检查，对明确有周边视网膜变性或伴干性裂孔的高度近视患者42例(45只眼)行氩离子激光光凝治疗。结果 高度近视患者42例(45只眼)氩离子激光光凝术后周边视网膜变性及干性裂孔区封闭良好，色素斑形成明显。LASIK术后6个月随访，术前行氩离子激光光凝的患者视网膜情况良好，未发生裂孔源性视网膜脱离。结论 LASIK术前对明确有视网膜变性或伴干性裂孔的高度近视患者预防性行氩离子激光光凝治疗，疗效确切，是预防LASIK术后出现裂孔源性视网膜脱离的重要措施。     

The role of laser wavelength in the treatment of vitreoretinal diseases

Advances in laser technology have provided ophthalmologists with lasers spanning the visible and near-infrared spectrum. Recently, prospective, randomized clinical trials have compared laser wavelengths in the treatment of specific disorders. The Krypton Argon Regression Neovascularization Study found no difference between argon blue-green and krypton red laser when performing panretinal photocoagulation to manage proliferative diabetic retinopathy. The Macular Photocoagulation Study Group and the Canadian Ophthalmology Study Group have independently found no substantial difference in treatment outcome when using argon green versus krypton red laser to treat choroidal neovascularization in eyes with age-related macular degeneration. These recent trials and others that evaluate laser management of proliferative diabetic retinopathy, choroidal neovascularization, retinopathy of prematurity, and retinal breaks are reviewed. Multiple studies have failed to identify a moderate difference in treatment outcome between treatments performed with different laser wavelengths; however, small differences in outcome cannot be excluded without further study involving great numbers of patients. At the present time, ophthalmologists should be reassured that individual preferences for one wavelength over another in specific situations should not have a major effect on the visual outcome of the procedure.     

眼内硅油取出术前激光光凝对防止视网膜脱离复发的效果观察

目的：观察视网膜脱离手术硅油填塞患眼在取出硅油前进行视网膜光凝对防止视网膜再脱离的效果。 方法：对24例24只施行过玻璃体视网膜手术和硅油填塞的视网膜脱离患眼,在取出硅油前2周至3个月时用氩绿或氪红激光在巩膜嵴后作全周或半周播散性光凝。硅油在注入后4～27个月(平均10.6个月)时取出。 结果：22只眼硅油取出后视网膜保持复位,占91.7%;2只眼分别因周边部原裂孔处附着不牢及前PVR发生视网膜再脱离,占8.3%。 结论：视网膜脱离手术硅油填塞患眼,取硅油前先行激光光凝,可减少硅油取出后视甲膜脱离的复发. （中华眼底病杂志,1997,13：197-198）     

Relative efficacy of the argon green, argon blue-green, and krypton red lasers for 10-0 nylon subconjunctival laser suture lysis

BACKGROUND AND OBJECTIVE: To determine the optimal wavelength for subconjunctival laser suture lysis. MATERIALS AND METHODS: 130 black monofilament 10-0 nylon sutures were sewn subconjunctivally into the bare sclera of enucleated rabbit globes. The lowest energy levels facilitating laser suture lysis were determined for the argon green (514.5 NM), argon blue-green (488.0 NM, 514.5 NM), and krypton red (647.1 NM) wavelengths. In addition, absorption spectroscopy was performed on the suture material and conjunctiva using the Perkin Elmer W/VIS Lambda 2 spectrometer. RESULTS: Krypton red produced the fewest buttonhole defects, and it was also the most efficient energy source for suture lysis (P = 0.0001) under nontenectomized conjunctiva. Absorbance spectra studies revealed peak absorbance at 628 NM for the 10-0 nylon suture material. CONCLUSIONS: Based on animal and absorption spectroscopy studies, krypton red may be a safer and more efficient wavelength for subconjunctival laser suture lysis.     

Massive choroidal haemorrhage as a complication of krypton red laser photocoagulation for disciform degeneration

A 78-year-old man with perifoveal subretinal neovascularization originally treated with krypton red laser was re-treated. An attempt was made to produce a "chalky white" burn at the site of the neovascular frond. Immediately after a burn, a brisk choroidal haemorrhage followed, apparently from a ruptured choroidal vessel. Bleeding occurred subretinally and into the vitreous, blinding the patient. While the krypton red laser carries advantages over the argon laser in the treatment of subretinal neovascular fronds, this case indicates that hard burns with the krypton laser carry a risk of massive subretinal haemorrhage.     

Transpupillary CW YAG laser coagulation. A comparison with argon green and krypton red lasers

The authors have developed a CW YAG laser for transpupillary coagulation. The effects of CW YAG coagulation on the retina, retinal vessels, and fovea were compared with those produced by the krypton red and argon green lasers. To produce threshold coagulative lesions in monkeys and rabbits, we needed five to ten times more energy with the CW YAG than with the krypton red or argon green lasers. Nerve fiber damage was observed only when coagulating retinal vessels with the argon green laser. At the parameters used, none of the lasers damaged the sensory retina of the fovea. The CW YAG may be used as a new mode of laser coagulation in the treatment of retinal diseases.     

Effects of red krypton and monochromatic green argon lasers in the foveal region. A clinical and experimental study

The destruction of senile neovascular membranes in the central avascular region of the macula using argon laser is difficult and associated with complications. Yellow pigment in this region absorbs the blue component of the conventional argon laser radiation. In this study, we compared laser of different wavelenghts: red krypton and green argon. Light and electron microscopic studies on non-human primates were performed at one hour and three weeks following laser burns. With the red krypton laser maximum damage was seen at the level of choriocapillaris and the choro?d, although the pigment epithelium was also destroyed. With the green argon laser the maximum absorption occurred at the level of the pigment epithelium. A clinical and angiographic study showed that the destruction of juxtafoveal neovascular membranes by both these lasers was possible after one or several treatment sessions. After an average follow-up period of 45 months, visual acuity was stable or improved in 10 out 17 eyes treated with the green argon laser and in 27 out of 53 eyes treated with the red krypton laser. Our results suggest that the red krypton laser offers a better alternative for the treatment of neovascular membranes located near the foveola since less unnecessary damage is induced. Outside the xanthophyllic area there is no major difference between the different wavelengths.     

MASSIVE CHOROIDAL HAEMORRHAGE AS A COMPLICATION OF KRYPTON RED LASER PHOTOCOAGULATION FOR DISCIFORM DEGENERATION

A 78-year-old man with perifoveal subretinal neovascularization originally treated with krypton red laser was re-treated. An attempt was made to produce a "chalky white" burn at the site of the neovascular frond. Immediately after a bum, a brisk choroidal haemorrhage followed, apparently from a ruptured choroidal vessel. Bleeding occurred subretinally and into the vitreous, blinding the patient. While the krypton red laser carries advantages over the argon laser in the treatment of subretinal neovascular fronds, this case indicates that hard burns with the krypton laser carry a risk of massive subretinal haemorrhage.     

间接镜氪激光光凝结合改进宽环扎治疗视网膜脱离

目的 讨论采用间接镜氪激光光凝结合改进宽环扎治疗视网膜脱离的临床疗效.方法 对41例41只眼PVRB级或以下的孔源性视网膜脱离病人行宽环扎、放液,部分病人联合玻璃体腔注气或平衡液,术后间接镜氪激光治疗视网膜裂孔.结果 视力提高:术后视力为3.87±0.74,术前视力为3.40±0.86,P<0.05.视网膜复位情况:41只眼中手术成功36只眼,5只眼复发性,成功率88.37%.5只眼复发性视网膜脱离,除1例外伤性视网膜脱离放弃手术外,其余患者均行玻璃体手术后复位.结论 对视网膜脱离术我们建议遵循手术方式简单、并发症少的原则.选择适当病例,间接镜氪激光光凝结合改进宽环扎治疗视网膜脱离是一种安全、简便、易操作、效果良好的方法.

Abstract：

Objective To assess the clinical result of the krypton laser photocoagulation using indirect ophthalmoscopy combined with improved encircling scleral buckles.Methods Forty-one eyes of 41 patients were treated with encircling scleral buckles and drainage, some combined with intravitreal injection of gas or balanced salt solution (BSS).All of the retinal breaks were treated with krypton laser photocoagulation using indirect ophthalmoscopy after surgery.Results The visual acuity improved (P<0.05).The reattachment of the retina: 36 eyes were successfully repaired, 5 eyes became recurrent retinal detachment (the reattachment rate was 88.37%).Among the 5 cases, 4 patients were successfully treated with vitrectomy except one patient of traumatic retinal detachment was given up.Conclusions The treatment of retinal detachment should follow the principles of simple surgical methods and fewer complications.The krypton laser photocoagulation using indirect ophthalmoscopy combined with improved encircling scleral buckles in the treatment of retinal detachment in proper cases is a safe, simple and convenient, easy operated and effective method.     

激光全视网膜光凝术激光量和疗效的临床分析

目的：探讨激光全视网膜光凝术激光量与疗效的关系。 方法：回顾性分析我院应用氩蓝绿和氪红激光全视网膜光凝治疗的新生血管性青光眼52只眼、视网膜中央静脉阻塞47只眼和增殖型糖尿病视网膜病变231只眼的临床资料。 结果：新生血管性青光眼激光全视网膜光凝术的有效平均视网膜光凝斑总数是1 500个左右，增殖型糖尿病视网膜病变及视网膜中央静脉阻塞激光全视网膜光凝的有效平均光凝斑总数是1 000个左右，二者的平均光凝斑总数有显著差异(P<0.01)。 结论：根据视网膜病变的病情不同，选择合适的激光波长和确保有效光斑的范围与密度是激光全视网膜光凝术成功的关键。 （中华眼底病杂志，1997，13：195-196）     

Comparison of retinal photocoagulation using pulsed frequency-doubled neodymium-YAG and argon green laser.

The photocoagulation effects on retinal and choroidal tissue of the argon green and pulsed frequency-doubled neodymium-YAG lasers were examined in rabbit eyes. In contrast to the continuous wave output of the argon green laser, the pulsed frequency-doubled neodymium-YAG laser produces a series of 1 microsecond pulses emitted at a repetition rate of 10 kHz. The high repetition rate results in pulse averaging, allowing relatively low peak powers to be used while producing average powers capable of thermal tissue effects. Photocoagulation lesions in the rabbit retina were placed in pairs using each of the lasers. Light microscopic comparison of the argon and neodymium-YAG burns revealed morphologically similar lesions for up to 14 days after photocoagulation, with damage predominantly at the level of the retinal pigment epithelium and outer retina. The high repetition rate, pulsed frequency-doubled neodymium-YAG laser produced thermal tissue effects similar to the continuous wave argon green laser.     

Outcomes after laser therapy for threshold retinopathy of prematurity

OBJECTIVE: To determine the anatomic outcomes of eyes treated with laser photocoagulation for threshold retinopathy of prematurity and to identify potential risk factors for unfavorable outcomes after treatment. DESIGN: Retrospective, noncomparative case series. INTERVENTION: Photocoagulation of the peripheral avascular retina with an argon or diode laser indirect ophthalmoscope. PARTICIPANTS: One hundred twenty eyes of 81 infants with threshold retinopathy of prematurity treated with laser photocoagulation from 1989 through 1997 with at least 12 months of follow-up after treatment. MAIN OUTCOME MEASURES: The principal outcome was the presence of an unfavorable anatomic outcome defined as a retinal detachment, macular fold, or retrolental tissue. RESULTS: One hundred nine of 120 eyes (91%) had favorable outcomes. Eleven eyes (9%) had retinal detachments, and 1 of the 11 also had retrolental tissue. Zone 1 eyes appeared to be 3.3 times more likely to have an unfavorable outcome compared with zone 2 eyes, but the 95% confidence interval (0.8-14.5) did not support this statistically. Twenty-four of 109 eyes (22%) experienced dragging of the temporal vessels. Those with zone 1 disease were 13.7 times more likely to experience temporal dragging compared with zone 2 eyes (95% confidence interval, 3.3-57.2). CONCLUSIONS: After laser photocoagulation for threshold retinopathy of prematurity, 91% of eyes had a favorable anatomic outcome. Compared with zone 2 eyes, zone 1 eyes may be more likely to have temporal dragging of the retinal vessels. Laser therapy is effective in the treatment of threshold retinopathy of prematurity.     

Binocular indirect argon laser photocoagulator.

The binocular indirect argon laser photocoagulator was newly designed to enable visualisation of the entire fundus during panretinal laser photocoagulation and to treat retinal tears immediately after buckling procedures of the sclera. The lamp housing of the binocular ophthalmoscope was remodelled and adjusted so that the laser beam and illuminating light are coaxial after leaving the ophthalmoscope. The blocking filter was permanently fixed in the eye-pieces to lighten the weight of the ophthalmoscope. This new delivery system of the laser beam supplies the clinician with a better view of the whole fundus than the standard slit-lamp delivery system, and may become the ideal method for panretinal photocoagulation in the treatment of diabetic retinopathy and central retinal vein obstruction and for the repair of retinal tears. However, a fine and delicate laser technique in the posterior pole does not suit the function of this new delivery system well. Proper use of photocoagulation therapy by combining the standard and the new delivery system of the laser beam is preferable, depending on the location and nature of the retinal lesions.     

Current management of choroidal neovascularization

Age-related macular degeneration is the leading cause of blindness in Americans over age 65. In 1982, the Macular Photocoagulation Study (MPS) established that argon laser photocoagulation reduces the risk of severe visual loss in eyes with extrafoveal choroidal neovascularization (CNV) associated with macular degeneration. Subsequently, similar results were found for histoplasmic and idiopathic choroidal neovascularization. There are also encouraging data on photocoagulation of CNV in other diseases and with different wavelengths. The MPS Group has found the krypton laser to be effective for juxtafoveal CNV secondary to histoplasmosis and is evaluating argon green and krypton red lasers for subfoveal CNV. Other investigators are evaluating laser treatment of CNV associated with myopic degeneration, pigment epithelial detachment, and angioid streaks. The new tunable dye laser may further expand our ability to treat this disorder. Until CNV can be prevented, laser photocoagulation remains the treatment of choice, and clinical trials should identify appropriate cases.     

Comparative effects of argon green and krypton red laser photocoagulation for patients with diabetic exudative maculopathy.

AIMS/BACKGROUND: Focal treatment of diabetic macular oedema is usually done using a haemoglobin absorbing wave-length, such as argon green laser. This study aimed to compare photocoagulation with argon green (514 nm) and krypton red (647 nm), which is poorly absorbed by haemoglobin, in the focal treatment of patients with diabetic exudative maculopathy. METHODS: A total of 151 eyes of 78 outpatients were assigned randomly to receive either argon green (n = 79) or krypton red (n = 72) laser treatment. Pretreatment and post-treatment ocular examinations included visual acuity, fundus biomicroscopic examination, and fluorescein angiography. A total of 141 eyes of 73 patients were available for evaluation after 1 year follow up. RESULTS: No statistically significant difference was found between the two treatment groups with respect to visual acuity results, resorption of hard exudates, and resolution of focal retinal oedema. CONCLUSION: Krypton red laser was effective in the treatment of diabetic exudative maculopathy. Our data suggest that differential absorption of the various wavelengths by haemoglobin within microaneurysms may not be an important factor for ultimate success of focal treatment.