97th DOG Annual Meeting 1999



I. Bruder, A. B├╝sching, U. Oberheide, H. Lubatschowski, H. Welling, W. Ertmer

The transscleral laser-cyclophotocoagulation has been established as an ultima-ratio-method for the treatment of glaucoma. However, considerable problems arise concerning the dosage of the energy to be deposited. They are due to the treatment zone being hidden from direct view and a very short exposure time for the laser-tissue-interaction. The consequences of an inadequate amount of energy are over- or undertreatment. Due to decreased success or complications re-treatment will be necessary. During the irradiation of the tissue by laser light, thermoelastic pressure transients are generated. In this study we investigate the feasibility of localizing the ciliary body by the detection of pressure transients. The possibility to on-line-control the degree of tissue damage during the treatment is assessed.

Method: We used a specially designed handpiece to apply short pulsed laser radiation with low energy levels to enucleated bulbs of pigs. The ciliary body was irradiated through the sclera in contact mode via a fibre optic. We used an adjusted pressure transducer to detect acoustic transients which had been generated in the area of absorption of the ciliary muscle or the pigmented epithelial layer, respectively. To gather information on axial resolution of the method we performed our mesurements in different distances to the corneo-scleral limbus. The results have been compared with histologic findings of the treated area. In order to correlate modifications of the signal to thermal damage of different degrees, we applied the same procedure after having produced laser-induced cyclodestruction.

Results: After adjusting the laser parameters we detected acoustic transients from which we could conclude the optical properties of the irradiated area. The axial resolution we obtained allowed the differentiation and measuring of the depth of the structures. With increasing level of ciliary destruction a marked change of the signal could be recorded.

Conclusion: This procedure can serve as an esssential tool for the on-line-control of the coagulation process. Thus, the laser parameters can be adjusted optimally to the progress of the treatment.

Laserzentrum Hannover e.V.