These cases illustrate the possibility of creating a detailed and accurate retinal structural map using high-speed FD OCT. The map is created from 100 consecutive B-scans made possible by the rapid imaging speed of the system, which also limits motion artifacts. Once the map is obtained, the data can then be viewed and manipulated in different ways, allowing the clinician to view dynamically the individual B-scans that make up the map.
Cases 1 and 2 illustrate the use of this technique to image macular holes. Using current technology, information in areas distal to the center of pathology could be overlooked because of the limited number of scans performed by conventional OCT imaging. In this technique, the entire region is mapped and areas of interest can be identified and closely examined, with freedom to inspect the surrounding areas distal to the obvious area of interest. The ability to scan the entire macular area may lead to a greater understanding of the pathogenesis of macular holes and lamellar macular holes; even a subtle area of vitreomacular interface abnormality in an unexpected area would not be overlooked.
Case 3 demonstrates the possibility of finding small defects on the retinal map that could be missed with current OCT imaging techniques. Smaller lesions such as these may prove especially challenging to locate in a patient with poor fixation. The technique we present may prove especially useful in this scenario because the high-speed FD OCT can rapidly create a complete macular structural map. The higher resolution images also allow more precise localization within the retinal layers. The images obtained in this case appear to correlate with standard OCT images of spontaneously regressed macular holes or macular microholes. Because the clinical history suggests the latter, this would represent the first high-resolution images of this entity.
Cases 4 and 5 illustrate possible applications of FD OCT mapping to cases of choroidal neovascularization. The highly detailed macular map provides a unique opportunity to perform in vivo histology of the entire membrane complex. In the clinical setting, a choroidal neovascular complex is classified, characterized, and localized based on its appearance on a fluorescein angiogram; however, its accuracy in determining the localization (type 1, type 2, or combined) is uncertain. Recent reports suggest that angiographic features alone might not be sufficient to make this determination.27
In addition, case 5 raises the question of whether fluorescein angiogram is adequate for determining the full extent of the CNV complex. Incomplete localization of the CNV by fluorescein angiography may, in part, explain some treatment failures. These cases illustrate the potential for FD OCT to accomplish these tasks, which may aid in selecting which patients would benefit most from submacular surgery versus other therapeutic interventions. Improved localization of CNV may also improve treatment outcomes of photodynamic therapy or thermal laser.
An additional benefit to having a detailed dataset is the ability to create reconstructed B-scans or C-scans. Although the resolution of these images is decreased, they can still provide additional perspectives that could be useful in the analysis of various lesions. Similarly, this detailed map could be used to calculate more accurate volumetric data regarding the macula. Current OCT systems rely heavily on interpolation to calculate macular thickness maps, which may be subject to error and variability in measurements. The new technique of detailed macular mapping would avoid such problems. This could be used to measure macular edema in an extremely precise and accurate manner, which would aid in evaluating the various treatments for this condition.
This, to our knowledge, is the first report of macular pathology mapping using FD OCT. Recently, a report was published that showed the use of FD OCT to create volumetric representations of various macular lesions, which is an extension of the technique we have illustrated in this article.16
Other reports have been published which demonstrate similar mapping techniques using time–domain OCT.17,18,28
In those time–domain models, however, the map was created from a series of C-scans, a potential weakness of which is that most clinicians rely on B-scans for evaluation of the retina. Therefore, high-quality B-scans are more desirable than C-scans. Because these time–domain models do not acquire B-scans, they would have to be reconstructed from C-scans, potentially limiting the image quality. Further evaluation of these tools will demonstrate whether these potential limitations can be overcome in a clinical setting.
In conclusion, a rapid-sweep serial OCT B-scan based on the FD model can be used to create a detailed retinal structural map. The map provides additional information that can be missed on single scans, provides an accurate way to image large or complex lesions, and can be helpful in imaging smaller lesions especially in the patient with poor fixation. In addition, this may prove to be a useful research tool to examine more closely a variety of macular diseases.