Selective Retina Therapy (SRT) targets the Retinal Pigment Epithelium (RPE) without effecting neighboring layers as the photoreceptors or the choroid. SRT related RPE defects are ophthalmoscopically invisible. Owing to this invisibility and the variation of the threshold radiant exposure for RPE damage the treating physician does not know whether the treatment was successful or not. Thus measurement techniques enabling a correct dosing are a demanded element in SRT devices. The acquired signal can be used for monitoring or automatic irradiation control. Existing monitoring techniques are based on the detection of micro-bubbles. These bubbles are the origin of RPE cell damage for pulse durations in the ns and μs time regime 5μs. The detection can be performed by optical or acoustical approaches. Monitoring based on an acoustical approach has already been used to study the beneficial effects of SRT on diabetic macula edema and central serous retinopathy. We have developed a first real time feedback technique able to detect micro-bubble induced characteristics in the backscattered laser light fast enough to cease the laser irradiation within a burst. Therefore the laser energy within a burst of at most 30 pulses is increased linearly with every pulse. The laser irradiation is ceased as soon as micro-bubbles are detected. With this automatic approach it was possible to observe invisible lesions, an intact photoreceptor layer and a reconstruction of the RPE within one week.
Selective retina treatment (SRT) is a laser based method to treat retinal diseases associated with disorders of the retinal
pigment epithelium (RPE) while preserving photoreceptors and choroid. Applying microsecond laser pulses to the 100-
200 strongly absorbing melanin granules inside the RPE cells induces transient micro bubbles which disrupt the cells.
Aim of this work is to understand bubble dynamics in clusters with respect to the influence of the adjacent retina. Bubble
dynamics were investigated in vitro on porcine RPE. An about 200 μm thick layer of agarose gel was applied to the RPE
layer in order to simulate the mechanical properties of retina. Different laser pulse durations from 1 ns (532 nm,
Nd:YAG) to 1.7 μs (527 nm, Nd:YLF) were used. The bubbles were investigated interferometrically (fiber
interferometer @ 830 nm) and with fast flash photography (25 ns flash duration). Bubble lifetimes were measured. The
results show that with retina phantoms the bubble formation threshold was reached at 2.5 times higher irradiation than
without retina phantom for 1.7 μs laser pulses. The microbubbles generated with 1 ns laser pulses were almost not influenced by the agarose layer. Irradiation twofold over bubble formation threshold resulted in 3.5 times longer bubble lifetimes for μs and 2 times longer for ns pulse durations, respectively.
Selective retina treatment (SRT) is a laser based therapy of retinal diseases associated with disorders of the retinal pigment epithelium (RPE) while preserving photoreceptors and choroid. Microsecond laser pulses applied to the 100-200 strongly absorbing melanin granules inside the RPE cells induce transient micro bubbles which disrupt the cells. Aim of this work is to understand bubble dynamics in clusters.
Investigations were carried out on porcine RPE explants and on a floppy disc based model system. Laser pulse durations
of 3 ns (532 nm, Nd:YAG) and 1.7 μs (527 nm, Nd:YLF) were used. Bubble dynamics was explored with a fiber interferometer (830 nm) and fast flash photography (25 ns). Bubble sizes, velocities and lifetimes were measured. Single nucleation sites, which coalesce after some μs, are observed with ns pulses. Using μs pulses, fewer but larger cluster sites are observed which become two times bigger at the same factor above threshold. A linear increase of the
bubble hight with radiant exposure is found for both pulse durations. RPE Bubble formation thresholds of 85 mJ/cm2
and 255 mJ/cm2 for ns and μs pulses are found, respectively. Typical expansion velocities are 5 m/s while collapsing
bubbles can reach 30 m/s. Bubble heights are up to 5 μm.
Earlier investigations on single melanosomes showed a bubble size limitation to 4 μm with μs pulses. The melanosome clusters do not show this size limit. It has to be investigated whether the results are transferable to whole eye globes.
Selective retina treatment (SRT) is a new laser based method to treat retinal diseases associated with disorders of the
retinal pigment epithelium (RPE). Applying microsecond laser pulses tissue damage spatially confined to the retinal
pigment epithelium (RPE) is achieved. The RPE cell damage is caused by transient microbubbles emerging at the
strongly absorbing melanin granules inside the RPE cells. Due to the spatial confinement to the RPE the photoreceptors
can be spared and vision can be maintained in the treated retinal areas. A drawback for effective clinical SRT is that the
laser induced lesions are ophthalmoscopically invisible. Therefore, a real-time feedback system for dosimetry is
necessary in order to avoid undertreatment or unwanted collateral damage to the adjacent tissue. We develop a dosimetry
system which uses optical interferometry for the detection of the transient microbubbles. The system is based on an
optical fiber interferometer operated with a laser diode at 830nm. We present current results obtained with a laser slit
lamp using porcine RPE explants in vitro and complete porcine eye globes ex vivo. The RPE cell damage is determined
by Calcein fluorescence viability assays. With a threshold criterium for RPE cell death derived from the measured
interferometric signal transients good agreement with the results of the viability assays is achieved.
Selective Retina Treatment (SRT) is a new method to treat eye diseases associated with disorders of the RPE. Selective RPE cell damage is achieved by applying a train of 1.7 μs laser pulses at 527 nm. The treatment of retinal diseases as e.g. diabetic maculopathy (DMP), is currently investigated within clinical studies, however 200 ns pulse durations are under investigation. Transient micro bubbles in the retinal pigment epithelium (RPE) are expected to be the origin of cell damage due to irradiation with laser pulses shorter than 50 μs. The bubbles emerge at the strongly absorbing RPE melanosomes. Cell membrane disruption caused by the transient associated volume increase is expected to be the origin of the angiographically observed RPE leakage. We investigate micro bubble formation and dynamics in porcine RPE using pulse durations of 150 ns. A laser interferometry system at 830 nm with the aim of an online dosimetry control for SRT was developed. Bubble formation was detected interferometrically and by fast flash photography. A correlation to cell damage observed with a vitality stain is found. A bubble detection algorithm is presented.
In selective retina treatment (SRT) spatial confined tissue damage in the absorbing retinal pigment epithelium (RPE) is
obtained by applying microsecond laser pulses. The damage in the RPE is caused by transient microbubbles forming
around the laser heated melanin granules inside the cells. For treatment of RPE related diseases, SRT is thought to share
the therapeutic benefits of conventional photocoagulation but without affecting the photoreceptors. A drawback for
effective clinical SRT is that the laser-induced lesions are ophthalmoscopically invisible. Therefore, a real-time feedback
system for dosimetry is demanded in order to avoid undertreatment or unwanted collateral damage to the adjacent tissue.
We develop a dosimetry system which uses optical interferometry for the detection of the transient microbubbles. The
system is based on an optical fiber interferometer which is operated with a laser diode at 830nm. We present current
results obtained with porcine RPE explants in vitro and complete porcine eye globes ex vivo.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.