As people age, they face an increasing possibility of developing cataracts, characterized by opacity of the crystalline lens in the eye. Cataracts are treatable with surgery, but operating on the eye requires the utmost precision. Imaging the anterior segment of the eye can guide ophthalmologists during cataract surgery, and it can help them manage postsurgical complications. In a review, James S. Wolffsohn and Leon N. Davies of Aston University in Birmingham, UK, describe techniques for anterior segment imaging, focusing on recent advancements.

Some techniques have specialized applications. For example, slit-lamp biomicroscopy is used extensively to examine for postsurgery complications, and phakometry measures the radius of curvature of the crystalline lens using reflected images produced by the optical interfaces in the eye. Other techniques, such as MRI and the Scheimpflug technique, which uses a camera perpendicular to a slit beam to create a section of the cornea and lens, have broader applications.

Ultrasound biomicroscopy uses high-frequency sonic pulses to show various features of the eye in 3- and 2-D, but it is invasive and not as precise as desired. As a result, it has fallen out of favor, and partial coherent interferometry is taking its place. Nevertheless, partial coherent interferometry cannot penetrate dense lenses as well as ultrasound biomicroscopy.

Of all the techniques, optical coherence tomography has advanced most rapidly. It noninvasively captures cross-sectional images at a resolution of 6 to 25 μm, and resolution of 1.4 μm has been achieved recently at 800 nm.

The reviewers conclude by comparing the strengths and weaknesses of the various techniques. They note that there is still a need for a clinical high-resolution and a noninvasive technique to image behind the peripheral iris. (Current Opinion in Ophthalmology, February 2007, pp. 32-38.)