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Trans-scleral Cyclophotocoagulation - An Experimental Investigation using HF Ultrasound

1Westphal G., 1Stachs O., 2Lemor R., 1Stave J., 1Guthoff R.,
1Universität Rostock, Augenklinik (Rostock)
2IBMT (St. Ingbert)

Purpose: During cyclophotocoagulation, transsclerally applied laser light (810nm) reduces the aqueous-producing structures of the eye. The aim of this investigation was to obtain information about intensity and distribution of tissue changes in the coagulation area.
Method: Limited volume coagulation in the ciliary body of fresh enucleated porcine eyes was achieved by means of an 810 nm diode laser. The laser application with variations in power (500-2500mW) und exposure time (1-10sec) was applied perpendicularly to the scleral surface. Structural changes of the ciliary body configuration were analysed by HF-ultrasound backscattering as well as 3D ultrasound biomicroscopy.
Results: Variances of the coagulated tissue can be evidenced in the reflected ultrasound signal (online) and in the 3D ultrasound volume data for laser power >1500mW and application times >3sec. Correlations between parameters of laser application and the time-dependent trend of the backscattering signal as well as tissue changes can be determined.
Conclusions: The 3D ultrasound biomicroscopy provide information about size and spread of these coagulation areas. The changes in the backscattering signal during coagulation are caused by both thermal effects and mechanical deformation of the coagulation area. This fact complicate the definition of unique break-off criterias for laser application.