With the increasing popularity of Webinars as a means of medical education, Eyetube.net has dedicated a channel to Webcasts and symposia on a broad variety of surgical and nonsurgical topics. By clicking on the “Webcasts” tab on the home page for Eyetube.net, busy physicians can stay up to date by viewing, at their leisure, complete seminars on a range of topics, from “Refractive IOL Symposium” (http://eyetube.net/webcasts/#refractiveiol2008) to “Treatment of Retinal Vein Occlusion” (http://eyetube.net/webcasts/#treatment-of-retinal-veinocclusion).

This month's column highlights four videos from the “Advanced Glaucoma Diagnostics” Webcast (http:// eyetube.net/webcasts/#advanced-glaucoma-diagnostics).

TEN YEARS OF PROGRESS IN OPTICAL COHERENCE TOMOGRAPHY IMAGING
In the first of four videos, Richard Lewis, MD, reviews the evolution of optical coherence tomography (OCT) imaging and the use of the Cirrus HD-OCT (Carl Zeiss Meditec, Inc., Dublin, CA) in optic disc analysis and glaucoma management. Dr. Lewis starts his presentation by showing just how far we have come in a relatively short time, as reflected by the increased precision and improved resolution of OCT imaging. In 1998, the first OCT devices were capable of acquiring 100 A-scans per second with an axial resolution of 15 μm. By 2008, the spectral domain Cirrus HDOCT could obtain 27,000 A-scans per second with a 5-7mu;m resolution. Advances in image quality and contrast have been equally impressive.

Dr. Lewis then describes the features of the automated optic nerve analysis that were made possible by these advances—everything from the acquisition of a cube scan around the optic nerve (in contrast to the operatordependent circle scan) to the determination of the location of the nerve and delineation of the nerve fiber layer. As Dr. Lewis points out, the current 200 X 200 A-scan cube OCT scan around the optic nerve results in more than 40 million unique data points that can be used for analysis and comparisons (Figure 1) (http://eyetube.net/?v=wosid).

SPECTRAL DOMAIN OCT: ADVANTAGES FOR GLAUCOMA
In the second video of the Webinar, Ike Ahmed, MD, focuses on the use of OCT for progression analysis in glaucoma patients. Dr. Ahmed attributes this feature to the evolution of spectral domain OCT, with the fast acquisition of enormously large data sets that can be used for sequential comparisons. In 1.5 seconds, a 6 X 6-mm cube of retina around the optic nerve is scanned. This allows for precise registration, a high level of reproducibility, and low variability—all variables that are necessary for accurate progression analysis.

Dr. Ahmed explains the two different ways to identify progression, either by trend analysis or by event analysis. Trend analysis relies on linear regression analysis performed on sequential OCTs of the patient performed over time. Event analysis defines progression as a predetermined change from that patient's own baseline scans (usually an average of two baseline scans). Of course, the same trend and event-based techniques can be applied to serial perimetric examinations.

In addition to event and trend analysis, Dr. Ahmed explains that there are three ways to diagnose progressive retinal nerve fiber layer (RNFL) loss. For deep and narrow focal defects, topographical change can be determined by viewing the RNFL map and inspecting for image progression (similar to the use of the deviation map for the detection of differences from the normative RNFL map). For shallower and broader focal defects, the familiar temporal superior nasal inferior temporal (TSNIT) map can be converted into a TSNIT profile progression plot, in which the patient's RNFL profile can be followed over time, and RNFL loss can be color coded as a decay from the baseline TSNIT plot. Finally, for diffuse RNFL defects, trend analysis performed on global, superior, or inferior RNFL thickness values can provide useful information on rates of progression (Figure 2) (http://eyetube.net/?v=mesla).

ANTERIOR SEGMENT IMAGING WITH CIRRUS HD-OCT
Dr. Lewis describes high-resolution OCT imaging of the anterior segment, cornea, and angle structures in the third video in this series. He calls this feature “one of the most undervalued capabilities of Cirrus HD-OCT.” Identification of angle structures (such as the scleral spur, Schlemm's canal, and Schwalbe's line) on anterior segment OCT can be an adjunct to clinical gonioscopy in the treatment decisionmaking process for glaucoma patients. Dr. Lewis presents several cases in which his visualization of subtle pathology proved to be invaluable to surgical planning. In one example, he demonstrates an anterior segment OCT positive provocative test that provides objective evidence of significant angle narrowing in low illumination (Figure 3) (http://eyetube.net/?v=siles).

AUDIENCE QUESTIONS
In the fourth and final video, Drs. Ahmed and Lewis answer numerous questions from the audience that were submitted during the live Webinar. Although replaying the Webinar on Eyetube.net does not allow for specific questions from the viewer, the detailed answers provided by the doctors offer insight into the use and limitations of the Cirrus HD-OCT in glaucoma patients (http://eyetube.net/?v=gopul).

CONCLUSION
As physicians practice medicine in this multimedia age, the sources of lifelong medical education continue to evolve. The Webcasts on Eyetube.net allow practitioners to keep up with the latest ophthalmological advances by simply sitting down in front of their computers. In addition to providing free ophthalmic education, these Webcasts can provide viewers with a pressure-free environment in which to evaluate new diagnostic and surgical equipment.

Section Editor Nathan M. Radcliffe, MD, is an assistant professor of ophthalmology at Weill Cornell Medical College, New York-Presbyterian Hospital, New York. He has served on the speaker's bureau for Carl Zeiss Meditec, Inc. Dr. Radcliffe may be reached at (646) 962-2020; drradcliffe@gmail.com.

Szilárd Kiss, MD, and Christopher E. Starr, MD, are assistant professors of ophthalmology at Weill Cornell Medical College in New York. They acknowledged no financial interest in the products or companies mentioned herein. Dr. Kiss may be reached at szk7001@med.cornell.edu, and Dr. Starr may be reached at cestarr@med.cornell.edu.