Experimental, ultrasonically induced lesions in the retina, choroid, and sclera

Lesions of the retina, choroid, and sclera were created in the proptosed eye of the rabbit with the use of focused ultrasound at 9.8 MHz. Exposure levels greatly exceeding those encountered in diagnostic systems were required. Histological examination of selected tissue samples, analysis of lesion-producing exposures, and lesion size variations suggest that thermal mechanisms are the principal cause of permanent tissue alterations. Subthreshold lesions, which consist of transitory effects, were observed. 'Threshold" lesions first manifested tansitory effects followed by permanent alterations which appeared within 24 hr. Suprathreshold lesions were evidenced by the immediate appearance of a highly blanched area with an overlying edema and occasional hemorrhage, appearing within 24 hr. The edema in these cases was resorbed within a few days, leaving behind a permanently blanched region. The threshold curve developed from these data is similar in shape to the threshold curve for light-induced lesions created with a commensurate focal spot.