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 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.
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.
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.
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