Acoustic microscopy of the human retina and pigment epithelium

An acoustic microscope uses sound waves rather than light to image a sample, and displays viscoelastic rather than optical properties. The Stanford instrument, operating at frequencies near 1,000 MHz, achieves resolution and magnification that is comparable to a light microscope. Using this instrument, we examined sections of normal human retina and pigment epithelium and found that characteristic degrees of acoustic attenuation or phase shift were produced by structures such as cell nuclei, rod and cone outer segments, Bruch's membrane, red blood cells, and ocular pigment. Resolution was better with thin than thick sections, and fixation did not significantly alter the acoustic properties of the tissues studied. A comparison of iris tissue from albino and pigmented rabbits showed that melanin was a particularly strong acoustic attenuator. Acoustic microscopy may provide a new and direct means of probing the physical structure of tissues and cells.