Search

Die selektive Retinatherapie (SRT) wird zurzeit als neue, schonende Laserbehandlungsmethode fur verschiedene Erkrankungen des Augenhintergrunds evaluiert, die mit einer reduzierten Funktion des retinalen Pigmentepithels (RPE) assoziiert werden. Mit der SRT wird im bestrahlten Areal lediglich das RPE behandelt, ohne die angrenzende neurosensorische Netzhaut mit den Photorezeptoren und die unter dem RPE liegende Aderhaut zu schadigen. Die Therapie fuhrt idealerweise zu einer Regeneration des RPE und einem gesteigerten Metabolismus am chorioretinalen Ubergang. Im Gegensatz zur etablierten Laserphotokoagulation, bei der die bestrahlten und umgebenden Areale der Netzhaut komplett verodet werden, bleiben bei der SRT Skotome vollstandig aus. Der Artikel gibt eine Ubersicht uber die Methodik und die Mechanismen zu selektiven RPE-Effekten und resumiert In-vitro- und vorklinische Ergebnisse zur Bandbreite der Selektivitat fur verschiedene Bestrahlungsparameter. Die Beschreibung einer optoakustischen Methode zur Online-Visualisierung der optisch nicht sichtbaren Effekte und damit zur Dosimetrie ohne angiographische Kontrolle runden die Ubersicht ab.

A2-E is the dominant fluorophore of lipofuscin in the retinal pigment epithelium. In an in-vitro setup, we determined the temperature-dependent changes of the A2-E fluorescence with the aim of also assessing the potential value of such measurements for determining retinal temperature by autofluorescence measurements during laser treatment.A2-E was biosynthesized and diluted in Dimethyl Sulfoxide (DMSO) to 1 microM. Fluorescence measurements were performed with a photospectrometer under various temperatures ranging from 20 degrees C to 75 degrees C. Autofluorescence was excited at 467 nm, and emission was detected around 632 nm.A2-E fluorescence intensity showed a linear decrease concomitant with temperature increment. At 75 degrees C, the fluorescence intensity decreased by 43% compared to at 20 degrees C. Fluorescence intensity was completely reversible dependent on the temperature, which cannot be explained by thermal A2-E alteration.If the A2-E temperature-dependent fluorescence in-vitro is transferable to human fundus auto-fluorescence, then it may be possible to apply an autofluorescence-based online detection device for noninvasive determination of fundus temperature during in vivo laser treatment. This is of clinical relevance, especially for the application of photodynamic therapy (PDT) and transpupillary thermotherpy (TTT).

Background and Objectives Selective treatment of the retinal pigment epithelium (RPE) by repetitively applying green μs-laser pulses is a new method for retinal diseases associated with a degradation of the RPE, which spares the neural retina. We investigated an alternative approach to realize repetitive μs-laser exposure by rapidly scanning a continuous wave (CW)-laser beam across the RPE. Study Design/Materials and Methods An Ar+ laser beam (514 nm) with a diameter of 18.75 μm was repetitively scanned across porcine RPE samples in vitro providing an irradiation time of 1.6 μs per point on the central scan axis. RPE cell damage was investigated by means of the fluorescence viability assay Calcein-AM. Results The ED50 cell damage is 305 mJ/cm2 when applying 10 scans with a repetition rate of 500 Hz. The threshold decreases with the number of scans, a saturation was found at 135 mJ/cm2 with more than 500 exposures applied. The depth of focus in beam direction is 350 μm, defined by an increase of the threshold radiant exposure by 20%. Conclusions Targeting of pigmented cells with high local resolution has been proved with a laser-scanning device. Looking ahead selective RPE-treatment, the adaptation of a laser-scanning device on a slit-lamp or into a modified retina angiograph seems to be an attractive alternative to the pulsed μs laser device. Lasers Surg. Med. 32:252–264, 2003. © 2003 Wiley-Liss, Inc.

Hintergrund. Die selektive RPE-Laser-Behandlung ist eine neue Technik, mit der selektiv das RPE geschadigt wird und die neurosensorische Netzhaut intakt bleibt. Ein Problem stellt die ophthalmoskopische Nicht-Sichtbarkeit der Laserlasionen dar. Es war daher Ziel dieser Studie zu untersuchen, ob die Fundus-Autofluoreszenz (AF), die ihren Ursprung im Lipofuscin der RPE-Zellen hat, durch den Laserschaden verandert wird, so dass dieses als nichtinvasive Behandlungskontrolle verwendet werden kann. Material und Methode. Es wurden 26 Patienten mit makularen Erkrankungen [Diabetische Makulopathie (DMP), Drusenmakulopathie (AMD) und Retinopathia centralis serosa (RCS)] mit kurzen repetitiven Laserimpulsen (800 ns) eines grunen Nd:YAG Lasers (Parameter: 532 nm, 100 und 50 Pulse bei 500 und 125 Hz; Spotdurchmesser: 200 μm, Pulsenergien: 70–175 μJ) behandelt. Die AF wurde mit 488 nm angeregt und durch einen Sperrfilter uber 500 nm detektiert (HRA, Heidelberg Engineering). Die Patienten wurden postoperativ zu unterschiedlichen Zeitpunkten mittels Ophthalmoskopie, Fluoreszenzangiographie und AF-Messungen untersucht (1 h; 1,6 Wochen; 3, 6, 12 Monate). Ergebnisse. Die Fluoreszenzangiographie zeigte eine Leckage der bestrahlten Areale uber eine Woche. Keine der Laserlasionen war wahrend der Behandlung ophthalmoskopisch sichtbar. Eine Identifikation der Laserherde war durch AF-Messungen moglich, die einen Intensitatsabfall bei 22 von 26 Patienten, insbesondere denen mit RCS und AMD, zeigten. Die Lasionen waren direkt nach der Behandlung als hypoautofluoreszente Laserspots sichtbar. Nach einer Woche wurden die Herde hyperautofluoreszent. Bei Patienten mit DMP waren die Messungen aufgrund von Odem und groserer Netzhautdicke in einigen Fallen nicht erfolgreich. Schlussfolgerung. Durch AF-Messungen konnen ophthalmoskopisch nicht sichtbare Lasionen nach selektiver RPE-Laser-Behandlung, insbesondere bei Patienten ohne Netzhautodem, dargestellt werden. Daher hat die AF das Potenzial, die invasive Fluoreszenzangiographie zur Verifikation des Lasererfolges in vielen Fallen zu ersetzen.

Fundus autofluorescence (AF) is derived from the lipofuscin contained by the retinal pigment epithelial cells. Using a scanning laser ophthalmoscope, two-dimensional AF measurements of the ocular fundus can be achieved. Directly after conventional photocoagulation and also after selective RPE laser treatment (SRT) with ophthalmoscopically non-visible laser lesions, irradiated areas reveal reduced AF, indicating RPE damage. Since the green treatment laser beam could also be used for AF excitation, the aim of this study was to evaluate whether absolute measurements of AF can be performed, and also possible changes in AF detected, online during SRT.SRT was carried out by use of a frequency-doubled Nd:YLF laser (wavelength 527 nm, pulse duration 1.7 micros, repetition rate 500 and 100 Hz, number of pulses 100 and 30, single pulse energy 50-130 microJ) in vitro (porcine RPE; retinal spot size 160 microm) and during patient treatment (retinal spot size 176 microm). During irradiation, fluorescence light from the RPE was decoupled from the laser light inside the slit lamp and detected by a photomultiplier or photodiode at wavelengths above 550 nm. Additionally, temperature-dependent fluorescence intensity measurements of A2-E, the main fluorescent component of lipofuscin, were performed in a different in-vitro setup.The intensity of AF decreased over the number of applied pulses during laser irradiation, and this trend was more pronounced in porcine RPE samples than during human treatment. In vitro, the AF intensity decreased by about 22%; however, only a weak signal was detected. When treating patients, the AF intensity was strong and the rate of decay of fluorescence intensity with number of pulses was greater when irradiating at 500 Hz than at the 100 Hz repetition rate. However, for both repetition rates the AF decay was merely up to 6-8% over the number of pulses per laser spot. Fluorescence intensity of A2-E decreased linearly with increasing temperature at about 1% per 1 degrees C and was completely reversible.Online measurements of AF during selective RPE laser treatment are possible and reveal a decay in AF as a function of the number of laser pulses applied to the RPE. If A2-E results can be transferred to RPE fluorescence, the AF decay could be related to the temperature increase within the tissue during treatment. Further clinical studies-in SRT as well as in conventional laser photocoagulation-might be able to show online AF changes on different areas of the retina and on different pathologies. Due to the temperature dependence of the fluorescence, on-line AF measurements during laser treatments such as photocoagulation or TTT may be able to be used as a real-time method for temperature monitoring.

In all fundus laser treatments of the eye, the temperature increase is not exactly known. In order to optimize treatments, an online temperature determination is preferable. We investigated a noninvasive optoacoustic method to monitor the fundus temperature during pulsed laser irradiation. When laser pulses are applied to the fundus, thermoelastic pressure waves are emitted, due to thermal expansion of the heated tissue. Using a constant pulse energy, the amplitude of the pressure wave increases linearly with an increase in the base temperature of between 30 and 80 degrees C. This method was evaluated in vitro on porcine retinal pigment epithelium (RPE) cell samples and clinically during selective RPE treatment with repetitive microsecond laser pulses. During the irradiation of porcine RPE with a neodymium-doped yttrium (Nd:YLF) laser (527 nm, 1.7 micros, 500 Hz repetition rate, 160 mJ/cm(2)) an increase in the base temperature of 30+/-4 degrees C after 100 pulses was found. During patient treatments, a temperature increase of 60+/-11 degrees C after 100 pulses with a 500-Hz repetition rate and 7+/-1 degrees C after 30 pulses with 100 Hz at 520 mJ/cm(2) was found. All measured data were in good agreement with heat diffusion calculations. Optoacoustic methods can be used to noninvasively determine retinal temperatures during pulsed laser treatment of the eye. This technique can also be adapted to continuous-wave photocoagulation, photodynamic therapy and transpupillary thermotherapy, or other fields of laser-heated tissue.

Objective: The selective damage of the retinal pigment epithelium (RPE) with repetitive µs laser pulses is a new technique for the treatment of several retinal diseases. RPE can selectively be damaged by simultaneously sparing off the adjacent photoreceptor tissue. Objective of this study is to investigate whether optoacoustic (OA) transients occurring during irradiation might be used to control the invisible treatment effect. Setup: A train of frequency doubled Nd:YLF laser pulses (527 nm, 1.7µs pulse length, 500Hz rep. rate) were applied via a laser slit lamp on porcine RPE samples. The acoustic transients were recorded with a broadband transducer. Results: At low radiant exposures (< 100 mJ/cm2) we found a bipolar pressure transient due to thermoelastic expansion of the RPE. The pressure waves from the individual pulses of one pulse train show nearly identical transients. The transients differ slightly from different sites on the sample. At higher radiant exposures (> 150 mJ/cm2), the OA transients differ from pulse to pulse within a pulse train, which can be attributed to microbubble formation around the strong absorbing melanosomes inside the RPE cells. FFT spectra of the OA transients show slight differences in the frequency spectrum with the different radiant exposures.

Introduction:A new treatment of different retinal diseases is the selective photodestruction of the retinal pigment epithelium (RPE) by repetitive us laser pulses sparing the adjacent photoreceptors. This has first been demonstrated in animal experiments by repetivie 5 us and 200 ns laser pulses. In a clinical trail, so far 35 patient with different macular diseases (drusen, diabetis, RCS) were treated with a train of us-laser pulses. Due to the ophthalmoscopic invisibility of the irradiated areas, fluorescein angiography post treatment is necessary to control the therapeutic effect. Subject of this study is development of an On-Line control system to monitor the selective photocoagulation of the retinal pigment epithelium.Material and Methods:In a first attempt, rabbits were treated with a train of 100 laser pulses using a frequency doubled Nd:YLF-laser. Pulse energies between 70-130 µJ and a pulse duration of 1.7 µs were used at a repetition rate of 500 Hz. The eyes were irradiated with a clinical slit lamp and the spot diameter on the retina was 160 µm. Furthermore, the auto fluorescence of patient eyes were measured during treatment. Assuming photocoagulation of the RPE-cell, one possibility for an On-Line detection system is the measurement of the auto fluorescence change during irradiation induced by thermal and mechanical destruction. A strong fluorophore of the RPE is lipofuscin, which excitation wavelength is between 460nm and 540nm and the fluorescence is wide banded between 580nm and 750nm. We use the treatment laser as excitation source. During the single pulse we get 300 kW/cm2for excitation. The fluorescence light is coupled out from the excitation light path by using a dichroic beamsplitter inside the slitlamp. The high excitation intensity allowed us to measure the fluorescence with a photodiode.Results:We will present the first in vivo results of our fluorescence measurements on eyes as function of pulse energy for On-Line control of the selective treatment of the retinal pigment epithelium. Other possible methods for on-line control will be discussed.