Ossoinig's angle of ultrasonic absorption and its role in the diagnosis of malignant melanoma.

Using standardized A-scanning, we have defined a method of quantitating the attenuation of ultrasound through intraocular mass lesions. In a retrospective study using 43 histologically proven melanomas, the attenuation of ultrasound through these tumors was characterized by an angle that we termed "Ossoinig's angle of ultrasonic absorption." This angle was measured on the static Ascans, and the values for melanomas clustered nicely in the 40 to 65 degrees range. The series of tumors also was used to illustrate previously published criteria for the ultrasound diagnosis of malignant melanomas, emphasizing their echographic differences from other lesions.