April 2010
Volume 51, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2010
Gentle Retinal Photocoagulation by Automatic Temperature Control
Author Affiliations & Notes
  • R. Brinkmann
    Institute of Biomedical Optics, University of Luebeck, Luebeck, Germany
    Medical Laser Center Luebeck, Luebeck, Germany
  • K. Schlott
    Institute of Biomedical Optics, University of Luebeck, Luebeck, Germany
  • L. Ptaszynski
    Medical Laser Center Luebeck, Luebeck, Germany
  • S. Koinzer
    University Hospital Schleswig-Holstein, University Eye Clinic, Kiel, Germany
  • M. Bever
    Medical Laser Center Luebeck, Luebeck, Germany
  • A. Baade
    Medical Laser Center Luebeck, Luebeck, Germany
  • R. Birngruber
    Institute of Biomedical Optics, University of Luebeck, Luebeck, Germany
  • R. Johann
    University Hospital Schleswig-Holstein, University Eye Clinic, Kiel, Germany
  • Footnotes
    Commercial Relationships  R. Brinkmann, P, P; K. Schlott, None; L. Ptaszynski, None; S. Koinzer, None; M. Bever, None; A. Baade, None; R. Birngruber, None; R. Johann, None.
  • Footnotes
    Support  BMBF: FKz 01 EZ 0732
Investigative Ophthalmology & Visual Science April 2010, Vol.51, 4274. doi:
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      R. Brinkmann, K. Schlott, L. Ptaszynski, S. Koinzer, M. Bever, A. Baade, R. Birngruber, R. Johann; Gentle Retinal Photocoagulation by Automatic Temperature Control. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4274.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: : The damage extent of the retinal photocoagulations depends on the temperature increase and the time of irradiation. So far, the temperatures are unknown due to intraocular variations in light transmission and RPE/choroidal pigmentation. Thus in practice, often too large burns are produced, which can lead to extended scotoma and bleeding in the worst case. The aim of this project focuses on a dosimetry system, which automatically generates a desired coagulation strength for every single coagulation spot. This widely improves the therapy and relieves the ophthalmologists from any dosimetry control.

Methods: : Experiments were performed on porcine eyes in vitro and dutch belted rabbits in vivo. Coagulations were performed with a standard clinical Nd:YAG-laser (Visulas, 532 nm), equipped with an interface to cease emission upon trigger. Simultaneously, low energy Q-switched Nd:YLF-laser pulses were applied to excite thermoelastic pressure waves from the RPE/choroid which are detected with a transducer embedded in the contact lens. The pressure amplitudes are used to calculate the temperature increase in realtime and the laser shut down.

Results: : The ED50 threshold temperature to for minimal visible lesions were determined for different laser irradiation times by the Probit algorithm. An exponential dependence similar to the Arrhenius curve was found, however, threshold temperatures are much lower than predicted by Arrhenius: 65°@50ms and 55°@300ms. Feeding the treatment laser to automatically cease irradiation at threshold consequently led to barely visible to invisible lesions in vivo. Spots with almost constant diameters could be achieved when shifting the threshold curve to stronger damage. Sizes smaller than the target spot diameter were reproducibly generated which is otherwise almost impossible to obtain.

Conclusions: : These preliminary results show very promising towards realization of an automatic dosimetry system to achieve homogenous well defined retinal coagulations, almost independent of the individual retina and eye properties.

Keywords: laser • retina • diabetic retinopathy 
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