Real-time control for transscleral cyclophotocoagulation.

Abstract

In transscleral cyclophotocoagulation, the surgeon cannot directly observe the applied laser effects. Overdosage, possibly resulting in unwanted pop effects, or underdosage with no therapeutic effect therefore often occur. Laser radiation passing through the sclera and ciliary body is partly reflected from the fundus and can be monitored from outside the eye by a detector system. Since all other parameters influencing the intensity of the recorded radiation are constant in time during one laser exposure, the time dependence of this radiation directly reflects the change of transmission of the treated tissue. The laser exposure therefore can be stopped by a computer when certain criteria of the recorded curves are fulfilled. In addition, the transmission curves are displayed on a monitor in real time, permitting the surgeon to interrupt the exposure. A Nd:YAG laser and a diode laser are connected to the device. After successful tests in enucleated porcine eyes which were evaluated histologically and in human cadaver eyes this method is applied to patients suffering from refractory glaucoma. The transmission curves from enucleated porcine eyes show that the 810-nm diode laser is more appropriate for this method than the 1064-nm. Nd:YAG laser, because the radiation output of the diode is more stable in time and the tissue absorption is higher, both resulting in a larger dynamical range of useful signal. The curves from the porcine eyes, the human cadaver eyes and the curves from patients show a typical shape which allows interruption of exposure either by the surgeon or by the computer program before a pop effect occurs. This new method increases the precision and safety of transscleral cyclophotocoagulation.