Biomedical subjects

R Birngruber

Publications and source records attributed to R Birngruber.

At least 19 recordsLinked to original sources

PubMed1995

Development of a new Er: YAG laser conception for laser sclerostomy ab externo: experimental and first clinical results.

The erbium:YAG laser is a preferable energy source for laser sclerostomy ab externo due to the high absorption of its radiation (2940-nm wavelength) in the aqueous parts of scleral tissue. It has thus far been a disadvantage that laser energy has to be transmitted from the laser source to the application site via very susceptible special optical fibers (ZrF). As a consequence of technical improvements, the laser source could be integrated into the application probe. Therefore, only a robust quartz fiber was necessary for contact application. A fiber diameter of 400 microns was chosen according to the experience gained in previous studies. A total of 24 eyes with chronical open-angle glaucoma were treated. A fistula end-point detection unit was developed for safe indication of a full-thickness perforation of the sclera. With a fiber diameter of 400 microns, a postoperative success rate of about 54% was achieved at 6 months follow-up. The automated full-thickness perforation detection prevented the application of additional, surplus laser pulses in the anterior chamber. The postoperative success rate could be improved over that achieved in previous studies. The new device/conception offers more technical reliability and is a further step toward minimally invasive fistulating laser surgery of open-angle glaucoma.

Erbium↗

PubMed1995

[Progress in laser sclerotomy ab externo] Enlarging the sclerostomy channel and local mitomycin administration].

In a previous study we presented our first results after sclerostomy using a pulsed erbium/holmium: YAG laser. At a fiber diameter of 300 microns a success rate of 20-30% was found after a 1-year follow-up. This study concentrates on the improvement of the parameters for filter survival. METHODS. The fiber diameter and thus the size of the fistula increased to 400 microns. Patients who had undergone fibrosis for a previous fistula were treated intraoperatively with topical mitomycin administration. RESULTS. After a follow-up of 6 months, filter function in the 300 microns group was maintained in 26% of the treated eyes (n = 23), while 400 microns fistulas were successful in 48% (n = 26). In the mitomycin-treated group (n = 6), sclerostomy achieved an IOP regulation in four patients. Postoperative hypotony was more frequent, but did not exceed 2 weeks. CONCLUSION. An increase in fistula diameter improves the long-term results of laser sclerostomy. Mitomycin is useful in maintaining filter function in patients with an unfavorable prognosis.

Antibiotics, Antineoplastic↗

PubMed1992

Response of the retinal pigment epithelium to selective photocoagulation.

Multiple short argon laser pulses can coagulate the retinal pigment epithelium selectively, while sparing the adjacent neural retina and choroid; in contrast, continuous-wave laser irradiation typically damages the neural retina and choroid. The healing response to selective photocoagulation of the retinal pigment epithelium was studied in rabbits during a period of 4 weeks. The lesions were never visible ophthalmoscopically. During the healing period, the epithelium was reformed by a single sheet of hypertrophic retinal pigment epithelial cells. In contrast to continuous-wave photocoagulation, only minimal inflammatory response was found. Retinal pigment epithelial cells showed clear signs of viability, eg, phagocytized outer segments. The local edema in the photoreceptor layer and subretinal space found in the early stage disappeared when the blood-retinal barrier was reestablished. The choriocapillaris remained unaffected. No subsequent damage to the photoreceptors was found. This type of photocoagulation may be useful for retinal pigment epithelium-related diseases, eg, diffuse diabetic macular edema.

Animals↗

PubMed1992

Mid-infrared laser ablation of the cornea: a comparative study.

The ablation thresholds and patterns of collateral damage in cornea produced by Er:YAG (2.94 microns) and Er:YSGG (2.79 microns) lasers were measured. Two different pulse durations, 200 microseconds (normal spiking mode) and 100 ns (Q-switched mode), were used at both wavelengths. In the normal spiking mode, damage zones of 16 +/- 2 microns and 39 +/- 7 microns and ablation thresholds of 250 +/- 20 mJ/cm2 and 420 +/- 35 mJ/cm2 were measured at 2.94 microns and 2.79 microns, respectively. In the Q-switched mode, damage zones of 4 +/- 2 microns and ablation thresholds of 150 +/- 10 mJ/cm2 were found irrespective of the laser used. The similarity between the results using the Er:YAG and Er:YSGG lasers in the Q-switched mode suggest that either laser can be used with equal effectiveness for corneal trephination.

Animals↗

PubMed1992

[Selective occlusion of ocular neovascularization by photodynamic therapy].

Photodynamic therapy (PDT) has successfully been used to induce vascular occlusion via endothelial damage and subsequent thrombosis. To increase the selective of this method for neovascularizations, characteristics in the ultrastructure of the proliferative vessel wall allow physiological vessels to be spared and predominantly neovascularizations to be occluded: (a) Due to the disturbance of the blood-retina barrier, free dye molecules accumulate within the vascular wall. Using a dye with prolonged retention, such as phthalocyanine (CASPc), it is possible to thrombose neovascularizations 24 h post injection while leaving the physiological vasculature of the anterior segment of the rabbit eye unaffected. (b) Proliferating endothelial cells express high numbers of low-density lipoprotein (LDL) receptors. Chlorin e6 (Ce6), a potent photosensitizer, is covalently bound to LDL. Intravascularly, ce6-LDL complexes selectively label neovascular walls. Since ce6-LDL is incorporated intracellular into enzymatically active lysosomes, photothrombosis is effectively achieved at low drug and light doses in vivo. In addition, the induced damage is spatially confined to the inner vascular lining. We conclude that carrier-mediated PDT may offer a new and sensitive approach for selective treatment of intraocular neovascularizations.

Animals↗

PubMed1991

Optical properties of human sclera, and their consequences for transscleral laser applications.

The spectral dependence of the optical properties of human sclera adjacent to the limbus was investigated and related to the potentials of transscleral photocoagulation. The total transmission, absorption, and reflection, as well as the angular distribution of the transmitted and reflected light were measured at five laser wavelengths (442 nm, 514 nm, 633 nm, 804 nm, and 1,064 nm), both for noncontact and contact applications. Absorption and scattering coefficients were determined using the Kubelka-Munk model for light propagation through a scattering tissue. The scleral transmission is only 6% at 442 nm but increases to 35% at 804 nm and to 53% at 1,064 nm. The absorption is high at short wavelengths with 40% at 442 nm but it is only 6% at 804 nm and 1,064 nm. The reflection is generally higher than 40% and shows little wavelength dependence. The transmitted light is scattered diffusely at short wavelengths, but at 804 nm and 1,064 nm it exhibits a fairly narrow angular distribution in forward direction. Fiber contact leads to an increase of transmission, with a factor of 3.5 at 442 nm, of 2.0 at 804 nm, and 1.5 at 1,064 nm. Our results indicate that the diode laser (804 nm) and the Nd:YAG laser (1,064 nm) with contact delivery are best suited for transscleral photocoagulation.

Absorption↗

PubMed1991

Application of the 1-microsecond pulsed-dye laser to the treatment of experimental cerebral vasospasm.

Laser energy of 480 nm was applied in 1-microsecond pulses varying between 2.2 and 10 mJ to in vitro and in vivo models of cerebral vasospasm. First, the pulsed-dye laser was applied intravascularly via a 320-microns fiber to basilar artery segments from six dogs. The segments were mounted in a vessel-perfusion apparatus and constricted to, on average, 70% of resting diameter by superfusion with dog hemolysate. Immediate increase in basilar artery diameter occurred to a mean of 83% of control. In a second model, the basilar artery was exposed transclivally in the rabbit. In three normal animals, superfusion of the artery with rabbit hemolysate resulted in a reduction of mean vessel diameter to 81% of control. Following extravascular application of the laser, vessels returned to an average of 106% of the resting state. In six rabbits, the basilar artery was constricted by two intracisternal injections of autologous blood. 3 days apart. Two to 4 days after the second injection, the basilar artery was exposed. Extravascular laser treatment from a quartz fiber placed perpendicular to the vessel adventitia resulted in an immediate 53% average increase in caliber to an estimated 107% of control. No reconstriction was observed over a period of up to 5 hours. Morphologically, damage to the arterial wall was slight. This preliminary investigation suggests that the 1-microsecond pulsed-dye laser may be of benefit in the treatment of cerebral vasospasm.

Animals↗

PubMed1991

Treatment of vasospasm with a 480-nm pulsed-dye laser.

Laser energy at a wavelength of 480 nm was applied in 1-microseconds pulses of 3 to 10 mJ to two models of vasospasm. Rabbit common carotid arteries (CCA's) were constricted chronically by the application of human blood within a silicone sheath. Peak vasospasm developed 24 to 48 hours later, and persisted for up to 6 days. Endovascular laser treatment was delivered to 40 CCA's via a 200-microns diameter silica quartz fiber introduced through the femoral artery. The CCA caliber increased from 60% of the pre-vasospasm control diameter to a minimum post-laser diameter of 83% of control. No instances of laser-induced perforation or of arterial thrombosis were observed for up to 60 days after treatment. Prophylactic laser application to nine normal vessels was able to attenuate the development of vasospasm if blood was applied immediately thereafter (88% vs. 59% of control diameter, p less than 0.02), but not if blood was applied 7 days later. Studies in 16 normal CCA's established that there was a considerable margin between the laser energy required to induce dilatation and that which caused perforation, providing that the fiber remained relatively central within the artery. Morphological examination demonstrated focal loss of endothelial cells immediately after laser application, followed approximately 7 days later by the development of areas of intimal hyperplasia. Only minimal changes were observed in the medial or adventitial layers. In a second study, the basilar artery of seven dogs was constricted chronically by two intracisternal injections of autologous blood 3 days apart. Five dogs received endovascular laser treatment 7 or 10 days after the first injection, when basilar artery diameter was reduced to a mean of 61% and 77% of control, respectively. Immediately following treatment, basilar artery diameter increased to 104% and 102% of resting diameter, respectively. Both untreated and laser-treated arteries were smaller than the control diameter at 30 days (80% and 82%, respectively), but in each group the vasodilatory response to hypercapnia was preserved. These findings indicate that 1-microsecond laser pulses are well tolerated by systemic and cerebral arteries in two different animal models, and suggest that the 480-nm pulsed-dye laser may have an application for the treatment or prophylaxis of cerebral vasospasm.

Animals↗

PubMed1991

[Microcoagulation of the fundus. Experimental results of repeated laser pulse exposure].

Angiographically visible lesions were produced in the fundus of rabbit eyes with repetitive 5 microseconds pulses and continuous wave exposures with 50-ms to 1-s pulse duration from an modified argon laser (514 nm). The ophthalmoscopic and the fluorescein angiographic findings showed less damage in the neural retina and the choroid after repetitively pulsed irradiation. Light microscopy and transmission electron microscopy showed that the neural retina and the choroid can mostly be spared by using repetitive 5 microseconds pulses, even though the damage to the retinal pigment epithelium is similar to the damage caused by continuous wave irradiation. Possible clinical applications, e.g. for macular edema and central serous retinopathy, are discussed.

Animals↗

PubMed1991

[Optical properties of human sclera and their significance for trans-scleral laser use].

The spectral dependence of the optical properties of human sclera adjacent to the limbus was investigated and related to the potentials of transscleral photocoagulation. The total transmission, absorption and reflection and the angular distribution of the transmitted and reflected light were measured at five laser wavelengths (442 nm, 514 nm, 633 nm, 804 nm, and 1064 nm) for both noncontact and contact applications. The scleral transmission is only 6% at 442 nm, but increases to 35% at 804 nm and 53% at 1064 nm. The absorption is high at short wavelengths, with 40% at 442 nm, but it is only 6% at 804 nm and 1064 nm. The reflection is generally higher than 40% and shows little wavelength dependence. The transmitted light is scattered diffusely at short wavelengths, but at 804 nm and 1064 nm it exhibits a fairly narrow angular distribution in the forward direction. Fiber contact leads to an increase in transmission, with a factor of 3.5 at 442 nm, of 2.0 at 804 nm, and of 1.5 at 1064 nm. Our results indicate that the diode laser (804 nm) and the Nd:YAG laser (1064 nm) are best suited for transscleral photocoagulation and that contact delivery leads to a reduction of the energy required for cyclophotocoagulation.

Ciliary Body↗

PubMed1990

Laser sclerostomy by pulsed-dye laser and goniolens.

We describe an ab-interno laser sclerostomy procedure using the method termed dye-enhanced ablation with a slit-lamp delivery system and special goniolens such that only the laser light beam penetrates the anterior chamber. The procedure uses a microsecond-pulsed-dye laser emitting at 666 nm and iontophoresis of methylene blue dye (absorption of 668 nm) into the sclera at the limbus to enhance the absorption of the laser light. We compared the number of pulses needed to perforate excised human sclera at pulse durations of 1.5, 20, and 300 microseconds. Pulse durations of 1.5 and 20 microseconds required 20 pulses or fewer to perforate excised human sclera with pulse energies of 75 to 100 mJ. The ab-interno laser sclerostomy procedure was performed in 54 eyes of Dutch-belted rabbits with pulse durations of 1.5 or 20 microseconds and a 100- or 200-microns incident spot diameter delivered using a CGF goniolens. Full-thickness fistulas were successfully created at both pulse durations in approximately 80% of eyes treated. A range of three to 25 pulses was required to perforate sclera with slightly fewer pulses and lower pulse energies at 1.5 microseconds compared with 20 microseconds. There were no significant complications from the procedure. This technique could permit filtration surgery to be performed on an outpatient basis.

Animals↗

PubMed1990

Semiconductor diode laser photocoagulation in retinal vascular disease.

The authors successfully performed clinical transpupillary retinal photocoagulation in 30 eyes of 26 patients with retinal vascular disease using a gallium-aluminium-arsenide (GaAlAs) diode laser emitting at 805 nm. Retinal photocoagulation was performed at treatment powers of 300 to 1300 mW and exposure durations of 0.2 to 0.5 seconds with a 200-microns diameter treatment spot. Patients treated with both diode and argon green lasers required 4.5 +/- 1.8 times greater mean laser energy with diode compared with argon to create ophthalmoscopically similar lesions. Parallel experimental retinal photocoagulation in Chinchilla rabbits required 3.1 +/- 0.9 times more power to create ophthalmoscopically similar lesions with the diode laser than with the argon laser. Intraoperative subretinal hemorrhage occurred rarely in patients with an incidence of 4 (0.44%) of 9021 treatment spots. Patients complained of moderate-to-marked pain in 10 (43%) of 23 treatments initiated under topical anesthesia. A transpupillary diode laser may be used clinically to perform therapeutic retinal photocoagulation.

Adult↗

PubMed1990

[Mechanism of action, scope of the damage and reduction of side effects in intraocular Nd:YAG laser surgery].

The damage mechanisms of intraocular Nd:YAG laser surgery and their respective damage ranges were investigated in vitro using bovine cornea specimens as a model tissue. The main damage mechanisms are plasma formation and expansion, emission of acoustic transients, and cavitation with jet formation. When a sequence of laser pulses is applied, the interaction of the acoustic transients with gas bubbles remaining from preceding laser exposures is also important. To distinguish the effects caused by the different physical mechanisms, laser pulses were aimed directly onto the corneal endothelium, and parallel to the cornea at various distances. Simultaneously, the cavitation bubble size was determined. The surface morphology and sections of the same lesions were studied by light and electron microscopy. The primary surgical mechanism is tissue evaporation by the laser plasma, whereas the collateral damage from single laser pulses is mainly caused by the cavitation and jet formation. The damage range after a 4-mJ laser pulse is 0.8 mm which is slightly larger than the corresponding cavitation bubble radius. The damage range of the acoustic transients produced by a 4-mJ laser pulse is several millimeters, when they can interact with small gas bubbles attached to the corneal endothelium. The damage range of the acoustic transients alone is smaller than that of cavitation as far as damage detected by light and scanning electron microscopy is concerned. However, on a subcellular level the acoustic transients may possibly cause damage up to a much larger distance. The damage range observed varies with the cube root of the laser pulse energy. A reduction of collateral effects therefore requires the use of small pulse energies. For energies of less than 1 mJ, the pulse duration has to be reduced to ensure plasma production. It is proposed to use low-energy picosecond pulses with moderate repetition rate instead of single nanosecond pulses to reduce collateral damage effects.

Animals↗

PubMed1989

Nd:YAG laser photodisruption of hemorrhagic detachment of the internal limiting membrane.

We used a Q-switched Nd:YAG laser to create an opening in the internal limiting membrane in three eyes with hemorrhagic detachment of the internal limiting membrane. In all instances, after membranotomy blood was rapidly cleared from the preretinal space resulting in prompt improvement in visual acuity. No retinal injury was observed. Nd:YAG laser photodisruption may be useful in the treatment of some cases of subinternal limiting hemorrhages.

Adult↗

PubMed1989

Corneal ablation by nanosecond, picosecond, and femtosecond lasers at 532 and 625 nm.

We produced corneal excisions with nanosecond (ns)-, picosecond-, and femtosecond (fs)-pulsed lasers at visible wavelengths. The threshold energy for ablation was proportional to the square root of the pulse duration and varied from 2.5 microjoules (microJ) at 100 fs to 500 microJ at 8 ns. Excisions made with picosecond and femtosecond lasers was ultrastructurally superior to those made with nanosecond lasers and, at pulse energies near threshold, showed almost as little tissue damage as excisions made with excimer lasers at 193 nm. We conclude that ultrashort-pulsed lasers at visible and near-infrared wavelengths are a possible alternative to excimer lasers for corneal surgery and might have advantages over conventional ophthalmic neodymium-YAG lasers for some intraocular applications.

Animals↗

PubMed1989

Picosecond optical breakdown: tissue effects and reduction of collateral damage.

The effects of picosecond laser-induced optical breakdown on tissue were investigated using high-intensity 40 ps Nd:YAG laser pulses at 1.06 microns. Tissue damage was evaluated using the corneal endothelium in vitro as a model system. Systematic studies were performed to determine the scaling of the tissue damage and damage range with pulse energy. For suprathreshold lesions, the radius of the damage zone varies as the cube root of the pulse energy, in agreement with simple physical scaling laws. A minimum damage range of less than 100 microns was observed for pulse energies of 8 muJ. Damage morphology was investigated by scanning electron microscopy. Three different damage patterns were observed; cell damage, cell removal, and rupture of Descemet's membrane. Different irradiation geometries were used to study damage mediated by either the shock wave or the cavitation bubble. Comparative studies using 10 ns pulses demonstrated that picosecond pulses yielded a significant reduction in collateral tissue damage.

Animals↗

PubMed1989

Laser output characteristics.

Certain aspects of laser radiation play an important role in laser safety. After a short description of basic laser principles, the unique characteristics of laser light are explained in a phenomenological manner. The enormously wide range of laser output parameters is demonstrated and correlated to typical medical laser applications. Temporal and spatial modes of laser operation are explained in greater detail because of their importance in laser safety.

Humans↗

PubMed1989

Clinical observations of six cases of laser injury to the eye.

During the last decade, five patients with laser injuries were examined at the University of Munich Eye Clinic, in addition to one laser-injury patient at the University of Erlangen Eye Clinic. From a review of these cases, it is possible to gain an insight into factors that led to the eye injuries and to predict the clinical sequelae of laser retinal injury. A possible means of treatment, using an ophthalmic Q-switched Nd:YAG laser, is suggested for some types of retinal injury involving vitreal hemorrhage.

Accidents, Occupational↗