Three optical techniques for visualizing ultrasound acoustic fields used for medical applications are described. The first technique is a type of shadowgraphy that can be realized using a simple optical system consisting of only a point light source and a camera. Characteristics of the images acquired using this technique are compared to those acquired using the Schlieren technique, and the advantage of this technique is demonstrated by visualization of an acoustic field of diagnostic short-pulsed ultrasound. The other two techniques are quantitative shadowgraphy and the phase-contrast technique. These techniques are designed for visualization of three-dimensional (3D) pressure distributions to replace hydrophone measurements. Their principles are explained in detail, and experimental results for visualization of a focused ultrasound field are discussed. The acquired images were quantitatively investigated with comparison to hydrophone measurements, demonstrating the usefulness of the techniques in quantitative evaluation of 3D ultrasound fields.