New applications in ultrasound technology.

Historical perspective It is only 50 years since ultrasound was first introduced to medical diagnosis; an astonishingly short period bearing in mind the impact this technique has exerted on all aspect of medical practices, including ophthalmology. In our field, the early pioneers of ophthalmic ultrasound include Mundt and Hughes, Oksala and Lehtinen, and Gernet. Those workers are credited with the introduction of time-amplitude A-scan. Oksala was the first to produce results on the speed of sound in various ocular structures, and Gernet described the application of this technique in axial eye length measurements. Ossoinig worked extensively on the refinement and “standardisation” of A-scan and on its utilisation in tissue diagnosis. The fundamentals of standardised A-scan include a precise S-shaped sound amplification curve, a transducer emitting nonfocused beam, and the external calibration of decibel gain by mean of “tissue model”. The technique of “standardised echography” as described by Ossoinig incorporates standardised A-scan, B-scan, and hand held continuous wave Doppler. This instrument combination coupled with well prescribed methods of examination is considered by many workers as the most accurate and reliable method of diagnostic ophthalmic ultrasound to date. Baum and Greenwood jointly reported the first application of “brightness modulated” B-scan in ophthalmology. They employed an immersion method. In 1972 Bronson and Turner described the first contact B-scan, making ultrasound an easy and patient friendly imaging modality. This, and other significant work by Purnell and Coleman et al, led to major expansion and popularisation of B-scan. The more recent development of duplex scanners and colour Doppler instruments in the 1980s has facilitated their use in ophthalmology. Workers such as Sergott, Leib, Williamson, Baxter, and GuthoV were responsible for the wider application of Doppler to ophthalmology. In 1990 Pavlin and colleagues described the first high frequency ultrasound (50–100 MHz) in ophthalmology and in 1991 published its clinical application in imaging of the anterior eye segment. The term ultrasound biomicroscopy (UBM) as coined by Pavlin is indicative of the high degree of magnification attained by this technique. Clear, near microscopic, in vivo images of the anterior segment, iris, ciliary body, and subsurface layers of the sclera and pars plana are now produced on UBM in such a way not previously possible on conventional B-scan. Buschmann and colleagues founded the international society for diagnostic ophthalmic ultrasound (SIDUO) in 1964. The society contains more than 500 members worldwide and is thought to be the oldest ultrasound forum of any medical specialty. SIDUO international congresses are held regularly every 2 years.