A third technique, known as Scheimpflug imaging, uses a rotating camera to photograph corneal cross-sections illuminated by slit beams at different angles (e.g., Pentacam). This method uses rapidly scanning projected slit beams of light and a camera to capture the reflected beams to create a map of the anterior and posterior corneal surface. Many topography machines rings (e.g., Atlas, NIDEK OPD-Scan) still utilize Placido discs but take the technique a step further, providing a computerized quantitative assessment of the corneal surface to provide more detailed information than one can appreciate by simply looking at the reflected.Ī second technique for corneal topographic assessment is the scanning slit technique (e.g., Orbscan). The posterior corneal surface cannot be characterized using Placido disc technology or a hand-held keratoscope. Similarly, hand-held keratoscopes (Figure 1B-C) are practical instruments that display concentric rings at the slit lamp for quick assessment of topographical changes (e.g., astigmatism induced by sutures). The pattern of light reflection reveals the shape of the anterior surface of the cornea (1). As the image from the Placido disc is projected on the cornea, some of the light is reflected off the tear film-air interface like a mirror. This technique characterizes the corneal surface by assessing the reflection of a set of concentric rings off the anterior corneal surface. The first advancement in assessing the shape of the anterior corneal surface was made in the late 1800s with the development of the Placido disc (Figure 1A) (1-2). Advances in digital photography and computer processing have vastly increased the utility of corneal topography (1). Devices now are able to characterize both the anterior and posterior corneal surfaces, creating a three dimensional map. Originally, corneal topography was only used to describe the anterior surface of the cornea. Continued abuse of our services will cause your IP address to be blocked indefinitely.Corneal Topography and Tomography Basic PrinciplesĬorneal topography is used to characterize the shape of the cornea, similar to how one would characterize a mountain using a topographic map. Please fill out the CAPTCHA below and then click the button to indicate that you agree to these terms.

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Pellucid crystal scans