Ultrasound Biometry

A-scan echography is used to measure the eye’s axial length. During A-scan biometry, the ultrasound beam must stay perpendicular to the anterior and posterior corneal surfaces, the anterior and posterior lens surfaces, and the retinal surface, forming an incidence angle of 90° with each of these surfaces. The immersion technique is preferred over the contact technique. Axial length measurements obtained with the contact technique were shorter than those obtained with the immersion technique by an average of 0.24 mm, mainly due to corneal compression. The A-scan patterns of the phakic, aphakic, and pseudophakic eye are described, along other challenging eyes such as the eyes with silicone-filled vitreous.