Krypton Laser Research Articles

Partial Ablation of Neovascular Membranes Involving the Fovea

To the Editor. —We read with interest the article by the Macular Photocoagulation Study Group, and Recurrent Neovascularization After Krypton Laser Photocoagulation for Neovascular Lesions of Ocular Histoplasmosis, 1 in the March 1989 issue of theArchives. Neovascularization persisted or recurred more frequently if treatment did not entirely cover the neovascularization or did not meet the required level of intense burn on the foveal side. Persistent neovascularization developed in 17% (17 of 102 eyes) of neovascular membranes (NVMs) that were completely treated, and in 39% (14 of 36 eyes) of NVMs that were incompletely treated. The authors emphasized that best results are obtained when the NVM is completely and intensely treated, implying that photocoagulation prevents recurrence of neovascular tissue by direct cauterization. However, Table 4 of their article notes that although 39% of incompletely treated NVMs persisted, 61 % of incompletely treated NVMs regressed! This implies that a successful outcome

Stable multi-line CW vibration laser near 5 μm based on F H(CN −) centers in CsBr

Stable cw laser operation has been obtained from F center/CN - defect pairs, “F H(CH -) centers”, in CsBr crystals. Pumped with the 676 nm krypton laser line in one of their electronic absorption transitions in the visible, the F H(CN -) centers perform (e-v) energy transfer into higher vibrational (v) levels of the CN - molecule and lase on their v=3→2 CN - vibrational transition near 5 μm up to a crystal temperature limit of ≈30 K. Using F H(CN -) defects with 12C 14N, 12C 15N, 13C 14N and 13 C 15N isotopes in the same crystal, we could obtain simultaneous four-line laser operation at 2010, 1980, 1970 and 1940 cm −1.

Partial Ablation of Neovascular Membranes Involving the Fovea-Reply

In Reply. —Drs Tornambe and Poliner raise interesting questions about the strategy for NVMs within the foveal avascular zone. However, we do not believe that treatment inside the foveal vascular zone remains a dilemma. Results in our initial report on the effectiveness of krypton laser photocoagulation in preventing loss of vision 1 showed that among eyes with neovascularization within 200 μm of the foveal center, 8% of treated eyes in comparison with 32% of untreated eyes had large losses in visual acuity (≥ 6 lines). While intentional partial of the neovascularization to spare receptors within the foveal avascular zone is appealing, we have misgivings about the strategy. The proposed partial is far less extensive than applied to eyes that were not completely covered in the Krypton Ocular Histoplasmosis Study. Subsequent persistent leakage from the NVM and its vision-threatening effects may overwhelm the benefit of sparing some

Raman scattering studies of Na DOPED SrxBa1-xNb2O6ceramics

Abstract Strontium barium niobate is a ferroelectric solid solution with tetragonal tungsten bronze structure. SBN described by the formula (SrxBa1-x) Nb2O6 with x = 0.25 to 0.75 is a room temperature ferroelectric crystal of space group P4bm. We have investigated the Raman spectrum and ferroelectric properties in order to study the effect of doping Na+ and the variation of Sr/Ba ratio. The 6471-Å line of a coherent radiation Krypton ion laser having an output power of 200 mW was used as the Raman source.

Iatrogenic Choroidal Neovascularization After Krypton Red Laser Photocoagulation

A major cause for failure of krypton red laser photocoagulation in patients with exudative age-related macular degeneration has been the development of recurrent choroidal neovascularization adjacent to the previously treated areas. After reviewing the possible causes of recurrences, it is apparent that a certain number are iatrogenic, ie, induced by krypton red laser causing disruption and damage to the pigment epithelium-Bruch's membrane-choroidal complex. We describe three separate episodes in two patients of iatrogenic recurrent choroidal neovascularization after krypton red laser photocoagulation.

Persistent and Recurrent Neovascularization After Krypton Laser Photocoagulation for Neovascular Lesions of Ocular Histoplasmosis

Persistence and recurrence of choroidal neovascularization after initial treatment with laser photocoagulation have been shown to be major contributors to loss of visual acuity. The 144 eyes assigned to krypton red laser photocoagulation in the Ocular Histoplasmosis Study-Krypton Laser were examined to describe persistence and recurrence in these patients. Persistent neovascularization was observed among 23% of treated patients and recurrent neovascularization was observed among an additional 8%. Both persistence and recurrence were accompanied by an increased frequency of severe visual loss. Patients with high blood pressure were more than 2.5 times as likely to have persistent neovascularization as patients without high blood pressure (95% confidence interval = 1.5, 4.8). Eyes in which the neovascular component of the complex was within 200 microns of the center of the foveal avascular zone were twice as likely to have persistent neovascularization (95% confidence interval = 1.2, 4.6). Eyes in which the treatment did not cover the neovascularization completely or did not meet the required level of intensity on the foveal side had a persistence rate approximately three times that of eyes in which the neovascularization was covered completely by intense, confluent burns (95% confidence interval = 1.7, 6.5). This last finding is of particular importance for ophthalmologists who treat similar patients.

A New Model of Experimental Choroidal Neovascularization in the Rat

Choroidal neovascularization in rat eyes was induced by krypton laser photocoagulation. Lesions were studied weekly by ophthalmoscopy, fundus photography, and fluorescein angiography. Morphologic correlation was provided by serial sectioning of lesions for light and transmission electron microscopy. In addition, vascular casts were prepared for scanning electron microscopy. Choroidal neovascularization occurred in 25 (60%) of 42 lesions, as evidenced by growth of capillaries through breaks in Bruch's membrane. In addition, 24 (28%) of 86 lesions studied by fluorescein angiography demonstrated leakage. This study provides the most complete angiographic, histologic, and ultrastructural documentation of experimental choroidal neovascularization in the rat. This model may be useful for in vivo studies of choroidal angiogenesis and its modulation via drug therapy.

A Model of Subretinal Neovascularization in the Pigmented Rat

We produced krypton laser photocoagulation lesions of mild to moderate whiteness in the posterior retinas of one eye of 23 pigmented rats, and identical appearing argon laser burns in the fellow eyes. We observed foci of subretinal neovascularization, histopathologically markedly similar to that which occurs in several human retinal diseases, in the krypton laser treated eyes of 6 of the 14 rats that were followed for one to three months after photocoagulation. No such lesions were observed in the argon laser treated fellow eyes, nor in krypton or argon laser treated eyes examined earlier than one month after photocoagulation. The photocoagulation damaged only the choriocapillaris, the retinal pigment epithelium (RPE), and the photoreceptor layer. In the acute lesions, we did not observe ruptures in Bruch's membrane. The neovascularization was surrounded by multiple layers of RPE cells, a histopathologic finding that has also been reported in some human eyes with subretinal neovascularization in age-related macular degeneration. These observations suggest that the RPE cells may be modifying the proliferative behavior of adjacent choroidal capillaries. This model differs from previous models of subretinal neovascularization in primates, and may be useful for additional studies of this important pathological process.

CLINICOPATHOLOGIC FINDINGS IN A PATIENT WITH SERPIGINOUS CHOROIDITIS AND TREATED CHOROIDAL NEOVASCULARIZATION

We present the ocular clinicopathologic features of the left eye of a patient who, during a 29-year period, developed the characteristic features of progressive serpiginous choroiditis. Two areas of choroidal neovascularization were successfully treated by laser photocoagulation. The larger area of neovascularization, located in and inferior to the maculopapillary bundle area and treated with argon laser, resulted in a scar composed of hyperplastic retinal pigment with persistence of neovascularization and full-thickness destruction of the retina. A smaller area of neovascularization, located temporal to the fovea and treated by krypton laser, resulted in a fibrous scar with obliteration of the new vessels and preservation of the inner retinal layers. A diffuse and focal infiltrate of lymphocytes was present in the choroid. Often, larger aggregates of lymphocytes were present at the margin of the serpiginous lesions. The serpiginous lesions were characterized by loss of retinal pigment epithelium and the photoreceptor cell layer. The margins of most lesions had variable degrees of hyperplastic retinal pigment epithelium and some had defects in Bruch's membrane, through which fibroglial scar tissue extended into the choroid.

Two-wavelength speckle interferometry on rough surfaces using a mode hopping diode laser

Two measurements performed on rough surfaced objects are described in this paper. The first sample is a mechanical component with a rather difficult accessible surface to be measured. A two-wavelength krypton laser interferometer with an effective wavelength of 36.47 μm has been used. The second example is a convex surface of a ground lens. Here a mode hopping diode laser interferometer with an effective wavelength of 2·020 mm has been used.

Krypton fluoride laser excited by high-power nanosecond microwave radiation

A lasing efficiency of 4% was achieved when an excimer laser utilizing an Ne–Kr–F2 mixture was pumped by a 200-MW nanosecond microwave pulse, the specific pump power being 1.4 MW/cm3. The absorption of the microwave energy in the active medium passed through a maximum at which the energy coupling efficiency approached 100%.

Reflection of laser light from ophthalmic contact lenses

Reflections of laser radiation from ophthalmological contact lenses are measured and hazard analysis calculations are presented. Measurements were made on the contact lenses using ophthalmic argon and krypton lasers. Reflection coefficients were around 0.2% for lenses with 'anti-laser' coatings and in the region of 4% for uncoated lenses. It can be shown that the nominal ocular hazard distance for a typical ophthalmic argon laser beam reflected from a contact lens with a flat front surface is approximately 30 cm for a coated lens and 1 m for an uncoated lens. The necessity of protective glasses for attending staff in particular circumstances is reviewed.

Juxtapapillary Exophytic Retinal Capillary Hemangioma Treated by Yellow Krypton (568 nm) Laser Photocoagulation

A 30-year-old man was found to have juxtapapillary exophytic capillary hemangioma complicated by circinate maculopathy and peripapillary exudative retinal detachment. The diagnosis was made from the appearance of the tumor and confirmed by fluorescein angiography. The presence of intermittent hematuria associated with a cystic kidney supported the diagnosis of von- Hippel-Lindau disease. subsequently, and attempt to treat the vascular lesion by yellow krypton (586 nm) laser photocoagulation failed to arrest the progression of the exudative retinal detachment, which finally became total.

Treatment of Small Choroidal Melanomas With Photocoagulation

Seventeen eyes with small choroidal melanomas presumed to be malignant were photocoagulated. The melanomas measured 7 to 15 mm at the tumor base and 2 t0 5 mm thick. First, photocoagulation using the green argon laser was aimed at closing the choroidal vascular supply of the tumor. In a second stage, tumor tissue was destroyed using the red krypton laser for confluent burns of long duration. Such treatment was supplemented by cryotherapy in peripherally located tumors or whenever photocoagulation alone did not result in tumor regression. Photocoagulation alone was used in ten eyes and combined wih cryotherapy in seven. After an average follow-up of 42 months, marked tumor regression was achieved in 12 eyes and some tumor regression in two. Tow eyes ultimately required proton beam irradiation, and one eye was enucleated. No metastasis occurred during follow-up.

Krypton laser for proliferative diabetic retinopathy: The Krypton Argon Regression of Neovascularization Study

The Krypton Argon Regression of Neovascularization Study (KARNS) is a multicenter, randomized, controlled clinical trial designed to determine the efficacy of red krypton laser photocoagulation in the treatment of proliferative diabetic retinopathy.

Laser pumping of Ho-, Tm-, Er-doped garnet lasers at room temperature

Laser pumping of Ho-, Tm-, and Er-doped garnets at room temperature is reviewed. Laser pumping of Tm (1860 nm), Ho (2090 nm), Er (1650 nm, 2710 nm) is possible with argon ion, krypton ion, and dye lasers. In Tm,Ho:YAG, efficient CW laser oscillation at 300 K is achieved under diode laser pumping. Er and Tm garnets might be pumped with diode lasers too. The highest slope efficiency of 41% is observed in Cr,Tm,Ho:YSGG under krypton laser pumping, demonstrating the efficient downconversion in this material. Red pump light is converted to the infrared spectral region at a quantum efficiency of nearly 2.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A study of the thermal switching behavior in GdTbFe magneto-optic films using two laser beams

An understanding of the thermal switching behavior of thin magneto-optic films is of primary importance for memory applications. We studied the formation of large domains induced by locally heating a GdTbFe layer with a krypton laser (753 nm) in a static magnetic field. The switching of the perpendicular magnetization was monitored in a small area of the larger krypton-laser-irradiated area by measuring the change in Kerr effect with a semiconductor laser (820 nm). It is observed that the switching is delayed with respect to the start of the heating pulse. There are strong indications that the delayed magnetization reversal starts simultaneously over the entire area of the heated spot and is followed by a small domain expansion.

Laser Treatment for Choroidal Neovascularization Outside Randomized Clinical Trials

This study was undertaken to determine whether the treatment benefit reported in randomized trials for patients with extrafoveal choroidal neovascular membranes (NVMs) secondary to age-related macular degeneration (AMD) or the ocular histoplasmosis syndrome (OHS) can be duplicated in other clinical settings. The visual results and recurrence rates in treated extrafoveal NVMs of 70 patients with AMD and 21 patients with OHS were similar to those reported by the Macular Photocoagulation Study Group, in which all treated patients received argon blue-green laser photocoagulation after the administration of retrobulbar anesthesia. In this study, 78% (71/90) of the patients were treated with krypton laser and only 35% (32/90) had retrobulbar anesthesia. These results suggest, but do not prove, that the wavelength of the laser used or the administration of retrobulbar anesthesia may not be critical variables in determining the success of treatment in patients with extra-foveal NVMs.

Cw laser action of Er3+ in double sensitized fluoroaluminate glass at room temperature

cw lasing at 1.6 μm was obtained for the first time in Cr, Yb, Er:fluoroaluminate glass. Double step pumping via Cr3+ and Yb3+ with a krypton laser yields a threshold pump power of 80 mW. Efficient lasing can be expected using glass samples of optimized dopant concentration and improved optical quality.

Optical dating studies of quartz and feldspar sediment extracts

Continuing developmental work into optical dating has led to some clarification of the optical behaviour of quartz and feldspar sediment extracts. We have verified the key assumption intrinsic to the method — that the optical signal is zeroed completely upon exposure to daylight. We also show that the rate of zeroing in optical dating is much more rapid than it is in TL dating. Studies concerned with the extraction of the thermally stable signal from laboratory-irradiated samples showed that problems may arise from medium-to-high-temperature preheating of young samples. Optical alternatives to thermal stabilization were tested using dye and krypton lasers. Using a krypton laser we have succeeded in obtaining an equivalent dose of 0.0 ± 0.7 Gy for the quartz from a modern intertidal sand, and an average dose of 120 ± 22 Gy for the feldspar extract of a ∼70 ka sand unit. Both were obtained using six wavelengths, from the infrared to the violet, and no dependence on wavelength was found. We found that the photon energies of infrared and deep red light can stimulate luminescence in unirradiated quartz and feldspar extracts of sediments. This was not expected, and suggests that the process of trap emptying is more complex than we had envisioned, but implies a far greater than expected degree of technical flexibility for the optical dating method.