Predicting visual outcomes for macular disease using optical coherence tomography

In recent years, the management of macular disease has undergone radical changes, in part because of new therapeutic approaches, but also due to the introduction of a new imaging modality-optical coherence tomography [OCT]. The application of OCT imaging has clarified many aspects of chorioretinal disease pathophysiology and elucidated many hitherto unrecognized disease characteristics. From an early stage in its development, OCT has also been revolutionary in attempting to extract clinically useful measurements from image data in an automated fashion. As a result, OCT-derived measurements of retinal thickness have been rapidly embraced in clinical and research settings. However, as knowledge of OCT image analysis has developed, it has become increasingly clear that even accurate measurements of retinal thickness may fail to predict visual outcomes for many diseases. As a result, the focus of much current clinical imaging research is on the identification of other OCT-derived anatomic biomarkers predictive of visual outcomes-such biomarkers could serve as surrogate endpoints in clinical trials and provide prognostic information in clinical practice. In this review, we begin by highlighting the importance of accurate visual function assessment and describing the fundamentals of OCT image evaluation, before describing the current state-of-the-art with regard to predicting visual outcomes, for a variety of macular diseases, using OCT

Spectral domain optical coherence tomography

Optical coherence tomography [OCT] allows high-resolution cross-sectional images of the neurosensory retina to be obtained in a non-invasive manner and has become an important tool for the diagnosis and management of vitreoretinal disease. OCT works by measuring the properties of light waves backscattered by tissue [analogous to ultrasonography] using an interferometer. In conventional OCT systems, light traveling in the reference path of the interferometer is reflected from a mobile reference mirror located within the instrument. OCT instruments that adopt this approach are often termed "time domain" as movement of the reference mirror allows assessment of the interference patterns generated as a function of time. Stratus OCT [Carl Zeiss Meditec, Dublin, CA], the most commonly used OCT system worldwide, is based on time domain technology. The requirement for a mobile reference mirror limits the image acquisition speed of time domain systems [Stratus OCT: 400 A-scans/second]. As a result, only sparse sampling of the macular area is possible in a single time domain OCT image set for any given patient. More recently however, the next generation of commercial OCT systems, boasting greatly increased image acquisition speed, has been released. These systems, termed spectral domain OCT, are based on the assessment of interference patterns as a function of frequency rather than that of time. With spectral domain OCT, A-scans can be acquired 50-100 times more quickly than in time domain systems, allowing dense sampling of the retina, volumetric rendering, and the generation of OCT fundus images. Spectral domain OCT is likely to supplant time domain OCT as the standard of care for retinal specialists, as it allows earlier detection of morphological changes in disease states and improved monitoring of disease progression over time