The best known method for healing retinal detachment is diathermic coagulation. Nearly every ophthalmologist has his special method for carrying out diathermic operations. All these methods lack a reliable control of the dosage, because the physical basis of diathermic coagulation has been neglected. My co-worker, Mr. Heinrich Kalmus, and I have found a convenient method of observing the process of coagulation in the measurement of the electrical resistance of the eye. From the variations of the resistance reliable conclusions may be drawn as to the state of coagulation. In this article adequate test methods and the results of experiments are described. On the basis of these experiments the relative values of the different methods of operation are considered. The knowledge of electrical resistance furnishes a convenient and accurate method to indicate the proper dosage of diathermic irritation in the human eye. SURVEY OF THE PREVIOUS LITERATURE The widespread