Anterior segment imaging has made tremendous strides since the introduction of slit lamp biomicroscopy. When the slit illumination device [1] of Swedish ophthalmologist Allvar Gullstrand was combined with Czapski 's binocular microscope in 1916, a major advance was marked as more accurate three-dimensional visualization and localization of anterior segment pathology became possible. Subsequent advances in anterior segment imaging have occurred primarily in three categories: (1) introduction of new imaging methods [ultrasound, confocal microscopy, and optical coherence tomography (OCT)], (2) progression from qualitative to quantitative analysis aided by advances in digital imaging, and (3) advances in end-user data representation [2].
Slit lamp biomicroscopy is an excellent case study of this progress. The coupling of photography to the slit lamp biomicroscope allowed clinicians to create permanent impressions of an exam, and these images became the preferred media for communicating clinical findings. Clinical atlases illustrating normal eyes and diseases of the anterior segment emerged. With the introduction of digital image acquisition, edge-detection algorithms allowed quantitative characterization of the anterior and posterior corneal surfaces, which provided the geometric information necessary to reconstruct surface elevations, curvatures, and thicknesses across a two-dimensional optical section. More recently, video acquisitions of rotating Scheimpflug sections [e.g., the Pentacam (Oculus) and the Galilei (Ziemer Ophthalmic Systems)] or horizontally scanning vertical slit beams [Orbscan (Bausch & Lomb Surgical)] have combined multiple two-dimensional sections to reconstruct the three-dimensional anatomy of the cornea. Similar advances are also occurring in the measurement of the anterior chamber, iridocorneal angle structures, and the lens. This chapter presents an overview of major imaging approaches in refractive surgery, including computerized videokeratography, arc-scanning ultrasound, Scheimpflug imaging, and anterior segment OCT. The focus is on clinical utility as well as caveats for practitioners who rely on the information these technologies provide.