Diode laser thermokeratoplasty – first clinical experience

Purpose: Pulsed holmium lasers are currently used to correct hyperopia by means of laser thermokeratoplasty (LTK). Series of μs laser pulses are applied with a high repetition rate to induce shrinkage of corneal collagen fibers. The pulsed energy application results in intrastromal temperature peaks of up to 200 °C. A continuously emitting laser diode can – as we demonstrated recently in an invivo study on minipigs – be used for LTK and may be of advantage because the temperature rise is more steady. The aim of this study was to examine the safety, amount, and stability of hyperopic correction of diode LTK on blind human eyes. Methods: We used a laserdiode that was set to continuously emit light at λ = 1.854 μm/μ_a = 1.04 mm^–1(group I, n = 4) or 1.87 μm/μ_a = 1.92 mm^–1 (group II, n = 4). Radiation energy was 100 to 150 mW for 10 s per coagulation. Eight coagulations on a single ring (group I) and 16 coagulations on a double ring (group II) diameter were applied in the cornea concentric to the entrance pupil by means of a vacuum-fixed application mask (group I = conjunctival fixation; group II = corneal fixation) and a handpiece with a focusing optic. Preoperatively as well as 1 week, 1, 2, 3, 6 12 and 18 months postoperative ophthalmologic controls were performed and the corneal refractive power was measured. Results: In group I initial refractive changes of up to + 4.9 D were achieved (1 week postoperative). However, due to the great penetration depth of the laser irradiation, large endothelial defects resulted beneath the stromal coagulations. In group II an initial refractive change of up to + 6.8 D was achieved and as a result of the reduced penetration depth, the endothelial cell damage was much reduced. Partial regression of the refractive effect occured in all subjects, which continued in higher refractive changes during the 2^nd postoperative year. The refractive effect at 12 months was + 0.6 to + 1.5 D in group I and + 0.9 to + 5.7 D in group II. At 12 months the induced astigmatism was 0.5 to 2.2 D in group I and 0.3 to 1.6 D in group II. No serious adverse effects were noticed. Conclusion: A continously emitting laser diode working at a wavelength of 1.87 μm can be used to correct hyperopia by means of LTK safely and effectively. Regression occurs predominantly in the first 6 postoperative months. Further studies must be conducted to determine the importance of patient inherent parameters such as age in establishing a nomogram.      

Correction to: A guide to classify tattoo motives in Mexico as a tool to identify unknown bodies

International Journal of Legal Medicine -     

Corneal optical coherence tomography before and immediately after excimer laser photorefractive keratectomy

PURPOSE: To investigate the representation of the corneal structure with optical coherence tomography before and immediately after excimer laser photorefractive keratectomy. METHODS: Twenty-four eyes of 24 patients with myopia and myopic astigmatism were prospectively studied. The corneal thickness and the corneal profile were assessed with slit-lamp-adapted optical coherence tomography preoperatively and immediately after excimer laser photorefractive keratectomy. RESULTS: The attempted mean spherical equivalent of the refractive corrections was -6.7 +/- 3.6 (mean +/- SD) diopters with a mean calculated stromal ablation depth of 91 +/- 38 microm. The corneal optical coherence tomography was reproducible in all patients, demonstrating a mean decrease of central corneal thickness after epithelial debridement and excimer laser photorefractive keratectomy of 118 +/- 45 microm. The comparison of the calculated stromal ablation depth and the corneal thickness changes determined by corneal optical coherence tomography revealed a significant linear relationship with a correlation coefficient of 0.88 (P <.001). The flattening of the corneal curvature was confirmed in all patients with the optical coherence tomography system and correlated with the attempted refractive correction (r =.82, P <.001). CONCLUSIONS: The slit-lamp-adapted optical coherence tomography system presented in this study allowed noncontact, cross-sectional, and high-resolution imaging of the corneal configuration. This initial clinical evaluation demonstrated that corneal optical coherence tomography could be a promising diagnostic modality to monitor corneal changes of thickness and curvature before and after excimer laser photorefractive keratectomy.     

Threshold determinations for selective retinal pigment epithelium damage with repetitive pulsed microsecond laser systems in rabbits

BACKGROUND AND OBJECTIVE: In both clinical and animal studies, it has been shown that repetitive short laser pulses can cause selective retinal pigment epithelium damage (RPE) with sparing of photoreceptors. Our purpose was to determine the ophthalmoscopic and angiographic damage thresholds as a function of pulse durations by using different pulsed laser systems to optimize treatment modalities. MATERIALS AND METHODS: Chinchilla-breed rabbits were narcotized and placed in a special holding system. Laser lesions were applied using a commercial laser slit lamp, contact lens, and irradiation with a frequency-doubled Nd:YLF laser (wave-length: 527 nm; repetition rate: 500 Hz; number of pulses: 100; pulse duration: 5 micros, 1.7 micros, 200 ns) and an argon-ion laser (514 nm, 500 Hz, 100 pulses, 5 micros and 200 ms). In all eyes, spots with different energies were placed into the regio macularis with a diameter of 102 microm (tophat profile). After treatment, fundus photography and fluorescein angiography were performed and radiant exposure for ED50 damage determined. Speckle measurements at the fiber tips were performed to determine intensity peaks in the beam profile. RESULTS: Using the Nd:YLF laser system, the ophthalmoscopic ED50 threshold energies were 25.4 microJ (5 micros), 32 microJ (1.7 micros), and 30 microJ (200 ns). The angiographic ED50 thresholds were 13.4 microJ (5 micros), 9.2 microJ (1.7 micros), and 6.7 microJ (200 ns). With the argon laser, the angiographic threshold for 5 micros pulses was 5.5 microJ. The ophthalmoscopic threshold could not be determined because of a lack of power; however, it was > 12 microJ. For 200 ms, the ED50 radiant exposures were 20.4 mW ophthalmoscopically and 19.2 mW angiographically. Speckle factors were found to be 1.225 for the Nd:YLF and 3.180 for the argon laser. Thus, the maximal ED50 -threshold radiant exposures for the Nd:YLF were calculated to be 362 mJ/cM2 (5 micros), 478 mJ/cm2 (1.7 micros), and 438 mJ/cm2 (200 ns) ophthalmoscopically. Angiographically, the thresholds were 189 mJ/cm2 (5 micros), 143 mJ/cm2 (1.7 micros), and 97 mJ/cm2 (200 ns). For the argon laser, the maximal ED50 radiant exposure threshold was 170 mJ/cm2 angiographically. CONCLUSION: The gap between the angiographic and the ophthalmoscopic thresholds for the 200 ns regime (4.5 times above angiographic ED50) was wider than for the 1.7 micros regime (3.3 times above the angiographic ED50). This would suggest the appropriate treatment would be 200 ns pulses. However, histologies have yet to prove that nonvisible mechanical effects increase with shorter pulse durations and could reduce the "therapeutic window." When comparing the thresholds with 5 micros pulses from the argon and Nd:YLF laser, it demonstrates that intensity modulations in the beam profile must be considered.     

Selective retina therapy in patients with central serous chorioretinopathy

Background Central serous chorioretinopathy (CSC) is a disease with a localized breakdown of the outer blood–retinal barrier located within the retinal pigment epithelium (RPE) causing subretinal fluid accumulation. Selective retina therapy (SRT) is a new, minimally invasive laser technology that has been designed to selectively target the RPE. SRT spares retinal tissue.Methods Twenty-seven eyes of 27 patients with active CSC were treated with SRT using a pulsed double-Q-switched Nd-YLF prototype laser (λ=527 nm, t=1.7 μs). At baseline, best-corrected visual acuity was determined and fluorescein angiography and optical coherence tomography were performed. The patients were followed for up to 3 months.Results After 4 weeks 85.2% of patients showed complete resolution of subretinal fluid and in 96.3% there was no leakage visible on fluorescein angiography. After 3 months 100% of patients demonstrated no subretinal fluid and 100% of patients had no leakage activity on fluorescein angiography. Visual acuity, 20/40 at baseline, improved to 20/28 after 4 weeks and to 20/20 after 3 months.Conclusion SRT is a safe and effective treatment for active CSC. Especially if the RPE leak is located close to the fovea, SRT is the favoured therapeutic option. We recommend earlier treatment of patients with acute CSC in order to prevent development of chronic changes due to CSC with irreversible anatomical and functional damage. SRT might be considered as a first-line treatment for active CSC.     

Transscleral and indirect ophthalmoscope diode laser retinal photocoagulation : Experimental quantification of the therapeutic range for their application in the treatment of retinopathy of prematurity

Laser indirect ophthalmoscope (LIO) photocoagulation and transscleral photocoagulation through the conjunctiva and subconjunctiva were performed in the fundus of chinchilla gray rabbits using various exposure times and powers, and the thresholds for retinal blanching and choroidal hemorrhage were determined. The therapeutic range was described for both applications as the ratio between energy values to produce grayish white lesions and hemorrhage at 50% probability. The therapeutic range appeared to remain almost constant with different exposure times. The mean ratio with LIO was 3.2±0.28, similar to that with slit-lamp delivery reported in our previous study. The mean ratio with transscleral photocoagulation through the conjunctiva and subconjunctiva were 2.48 ± 0.28 and 2.38 ± 0.26, respectively. The variability of LIO appeared to be a little lower than with transscleral photocoagulation. There was no significant difference between the variability with transscleral photocoagulation through the conjunctiva and subconjunctiva.     

Three-dimensional topographic angiography in chorioretinal vascular disease

PURPOSE: To evaluate a new angiographic technique that offers three-dimensional imaging of chorioretinal vascular diseases. METHODS: Fluorescein (FA) and indocyanine green angiography (ICGA) were performed using a confocal scanning laser ophthalmoscope. Tomographic series with 32 images per set were taken over a depth of 4 mm at an image frequency of 20 Hz. An axial analysis was performed for each x/y position to determine the fluorescence distribution along the z-axis. The location of the onset of fluorescence at a defined threshold intensity was identified and a depth profile was generated. The overall results of fluorescence topography were displayed in a gray scale-coded image and three-dimensional relief. RESULTS: Topographic angiography delineated the choriocapillary surface covering the posterior pole with exposed larger retinal vessels. Superficial masking of fluorescence by hemorrhage or absorbing fluid did not preclude detection of underlying diseases. Choroidal neovascularization (CNV) appeared as a vascular formation with distinct configuration and prominence. Chorioretinal infiltrates exhibited perfusion defects with dye pooling. Retinal pigment epithelium detachments (PEDs) demonstrated dynamic filling mechanisms. Intraretinal extravasation in retinal vascular disease was detected within a well-demarcated area with prominent retinal thickening. CONCLUSIONS: Confocal topographic angiography allows high-resolution three-dimensional imaging of chorioretinal vascular and exudative diseases. Structural vascular changes (e.g., proliferation) are detected in respect to location and size. Dynamic processes (e.g., perfusion defects, extravasation, and barrier dysfunction) are clearly identified and may be quantified. Topographic angiography is a promising technique in the diagnosis, therapeutic evaluation, and pathophysiological evaluation of macular disease.     

Selective Retina Therapy (SRT)

Selective Retina Therapy (SRT) is a new and very gentle laser method developed at the Medical Laser Center Lübeck. It is currently investigated clinically in order to treat retinal disorders associated with a decreased function of the retinal pigment epithelium (RPE). SRT is designed to selectively effect the RPE while sparing the neural retina and the photoreceptors as well as the chorioidea. Aim of the therapy is the rejuvenation of the RPE in the treated areas, which should ideally lead to a long term metabolic increase at the chorio-retinal junction. In contrast to conventional laser photocoagulation, which is associated with a complete thermal necrosis of the treated site, SRT completely retains full vision. This paper reviews the methods and mechanisms behind selective RPE effects and reports the first clinical results. An online dosimetry technique to visualize the ophthalmoscopically invisible effects is introduced.     

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.