Ultrasonics and its achievements in the 20th century are based on the ultrasound. Ultrasound waves have frequency from 20 000 Hz to 100 000 MHz.
There are three techniques of diagnostic ultrasonography: A-scan, B-scan and C-scan.
A-scan is mainly used for examination of the globe of the eye and its contents. The ultrasonic frequency of the transducer is 10 MHz. The probe is placed on various sections of the cornea or sclera and ultrasound waves are focused in different directions inwards. The echoes viewed on the screen are: 1) an echo of the cornea; 2) an echo of the anterior lens surface; 3) an echo of the posterior lens surface and 4) an echo of the posterior eye wall.
B-scan is mainly used for examination of the orbit and its contents. The image is two-dimensional.
Eye ultrasonography has a good application in the diagnosis of various processes in the eye globe and it is of particular value in a non-transparent environment. Retinal detachment, for example, is identified due to an additional echo in front of the eye fundus. The ultrasound image shows the size of the detachment but it should be over 1mm to be detected by the sonograph. Ultrasonography helps identify tumours, choroidal detachments, foreign bodies and other disorders in the anterior eye segment – in the iris, lens and cornea.
Ultrasonography is used in ophthalmology for ultrasound biometry to measure the anatomic and optical elements of the eye. Echometry deals with measuring the eye parts – corneal thickness, lens, diameter of the vitreous, ocular axial length.