Ophthalmologists routinely use stereoscopic photography, scanning laser ophthalmoscopy, scanning laser polarimetry, and time-domain optical coherence tomography (OCT) to identify glaucomatous changes in the optic nerve and retinal nerve fiber layer (RNFL). Like any diagnostic technology, however, these imaging modalities have strengths and weaknesses that affect their utility for diagnosing and tracking the progression of glaucoma. Fortunately, ophthalmologists now have access to Fourier-domain OCT, an advanced technology that overcomes many of the limitations of time-domain OCT.
Advances in surgical therapy have also improved the management of glaucoma. For example, selective laser trabeculoplasty (SLT) reportedly has an excellent safety profile,1 causes little to no damage to the trabecular meshwork, and is potentially repeatable.
In this supplement to Glaucoma Today, David S. Greenfield, MD, and David Huang, MD, PhD, demonstrate the clinical utility of Fourier-domain OCT. Mark Latina, MD, the inventor of SLT, presents an overview of this surgical technique and discusses its place in the glaucoma treatment algorithm.
TIME-DOMAIN VERSUS FOURIER-DOMAIN OCT
"Time-domain OCT has limited clinical utility. Its dependence on mechanical scanning constrains the amount and quality of the acquired data," said Robert N. Weinreb, MD, in an interview with GToday. "It also is limited by a relatively slow scanning speed (400 A-scans per second), the use of software to interpolate between data points, difficulty imaging through opaque media, and the skill of the operator. All these factors can introduce artifacts and affect the scan's utility for detecting changes in the RNFL and the optic nerve."
In contrast, Fourier-domain OCT uses a stationary reference mirror to perform 26,000 A-scans per second. This high rate of acquisition produces detailed images.
SHIFTING PARADIGM
Under the traditional paradigm, the diagnosis of glaucoma depends on concurrent changes in ocular function (eg, visual fields) and structure (eg, thinning of the RNFL). An emerging paradigm states that changes in structure need not be accompanied by the loss of function to be indicative of glaucoma. Any technology that detects subtle structural changes in the optic nerve and RNFL, therefore, would be a valuable tool for diagnosing early glaucoma.
EARLY DETECTION, EARLY TREATMENT
Early diagnosis is just the first step in effectively managing glaucoma. The sooner clinicians initiate treatment, the longer patients are likely to retain functional vision.
"Three decades after the introduction of laser trabeculoplasty, this procedure is recognized throughout the world as a viable therapy for most patients with open angle glaucoma," said Dr. Weinreb. "In fact, SLT is so safe, well-tolerated and effective that it no longer is reserved only for those patients who have been advanced to maximal tolerated medical therapy." Although careful clinical studies and economic analyses are needed to understand the value of SLT, Dr. Weinreb added, he believes that clinicians can comfortably justify using SLT as first- or second-line treatment for some patients.2
CONCLUSION
When used together, Fourier-domain OCT and SLT may advance ophthalmologists' understanding of glaucoma and significantly affect how they diagnose and treat this disease in the future.
