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Online autofluorescence measurements during selective RPE laser treatment

  • Laboratory Investigation
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Graefe's Archive for Clinical and Experimental Ophthalmology Aims and scope Submit manuscript

Abstract

Background

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.

Methods

SRT was carried out by use of a frequency-doubled Nd:YLF laser (wavelength 527 nm, pulse duration 1.7 µs, repetition rate 500 and 100 Hz, number of pulses 100 and 30, single pulse energy 50–130 µJ) in vitro (porcine RPE; retinal spot size 160 µm) and during patient treatment (retinal spot size 176 µm). 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.

Results

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°C and was completely reversible.

Conclusions

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.

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Acknowledgements

The authors wish to thank F.G. Holz from the University Eye Hospital Bonn in Germany and his group for providing the A2-E and M. Pierce from the Wellman Laboratories of Photomedicine at the Massachusetts General Hospital, Harvard Medical School, Boston, USA for proofreading the manuscript.

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Authors and Affiliations

  1. Medical Laser Center Lübeck, Lübeck, Germany

    Carsten Framme, Georg Schüle, Reginald Birngruber & Ralf Brinkmann

  2. University Eye Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93042 , Regensburg, Germany

    Carsten Framme & Johann Roider

Authors
  1. Carsten Framme
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  2. Georg Schüle
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  3. Johann Roider
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  4. Reginald Birngruber
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  5. Ralf Brinkmann
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Corresponding author

Correspondence to Carsten Framme.

Additional information

Proprietary interest: One of the authors (R.B.) has a patent on the laser technique used in this study

Presented in part at the annual meeting of the Deutsche Ophthalmologische Gesellschaft (DOG), Berlin, 2003

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Framme, C., Schüle, G., Roider, J. et al. Online autofluorescence measurements during selective RPE laser treatment. Graefe's Arch Clin Exp Ophthalmol 242, 863–869 (2004). https://doi.org/10.1007/s00417-004-0938-3

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  • DOI: https://doi.org/10.1007/s00417-004-0938-3

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