In 1949, Ludwig used ultrasound to detect gallstones in patients. The first publication on the use of ophthalmologic ultrasound appeared in the medical literature in 1956. By the mid-1970s, ophthalmologists were using ultrasound to determine axial length in a clinical setting. These measurements facilitated calculations of intraocular lens power which led to a revolution in cataract surgery. Further innovations came when Baum and Greenwood introduced their two-dimensional B-mode image to ophthalmology. Soon afterwards, Bronson developed a hand-held contact transducer for this type of image acquisition which led to the rapid dissemination of ultrasound devices within ophthalmology clinics. The B-mode images could be used to delineate accurately retinal detachments, vitreous membranes, and choroidal tumors. In the early 1990s, new technology made it possible to image the anterior segment of the eye with devices that captured images at higher frequencies of 35–50 MHz. This improved image resolution four- to fivefold and is still the gold standard for analysis of certain anterior-segment disease such as ciliary body effusions, infiltrates, and tumors.