[The new OCT generation offers deep insights: imaging of the choroid using the Cirrus OCT]

BACKGROUND

Until now depiction of the choroid using time domain optical coherence tomography (OCT) (Stratus III) was barely possible. Visualization of choroidal perfusion was carried out using indocyanine green angiography (ICGA). The spectral-domain OCT, such as Cirrus OCT (C-OCT) is able to image the choroid better because it offers higher resolution, increased penetration depth of the scan beam and faster acquisition of A-scan data. The aim of the study was to evaluate the potential of choroidal imaging in patients suffering from macular disease.

METHODS

The advanced visualization tool of C-OCT was primarily used and converted to a z-axis topography. Because of a special algorithm developed by our team, targeted imaging of the choroidal vessels was possible through the scanned two dimensional retinal areas. This image offers an extended image of choroidal vessels (large and small vessels) in several levels. In total 20 patients eyes (n = 15 with various macular diseases and n = 5 normal conditions) who underwent C-OCT and ICG angiography (HRA 2) were chosen to participate in this special algorithm. A precise correlation of ICG and choroid OCT in a semitransparent manner was carried out.

RESULTS

The first prototype of the recognition software prototype produced clear imaging of the choroid in 100% of cases but only in 55% in the macular region depending on the extent of macular disease. Limitations were low signal intensity and penetration depth as well as a poorly defined retinal pigment epithelium (RPE) and choriocapillaris especially in macular diseases of the RPE layer. After a black and white conversion in OCT using the software it was possible in all cases to integrate the choroidal OCT with the ICG angiogram in a semitransparent manner. This confirms that the choroidal vessels in C-OCT correlated identically with the ICG angiography. In contrast to the ICG where the contrast agent in the vessel emits a signal, the choroidal vessels are visible due to different reflectivity in the merging tissue.

CONCLUSIONS

These investigations showed that non-invasive topographic imaging of the choroid using spectral domain OCT, such as Cirrus OCT is now possible. Distinguishability of smaller vessels was excellent. The ICG (perfusion) and C-OCT (morphology) methods are two very different vessel imaging techniques. The integration of both methods is possible. The clinical relevance of the new image information still has to be researched.

[Optical coherence tomography for macula diagnostics. Review of methods and standardized application concentrating on diagnostic and therapy control of age-related macula degeneration]

BACKGROUND

Optical coherence tomography (OCT) has gained increasing relevance for follow-up after the treatment of macular diseases especially after anti-VEGF therapy. Therefore it seemed reasonable to develop standardized evaluation strategies and OCT examination guidelines for Stratus OCT III.

MATERIALS AND METHODS

Basic guidelines for the Stratus OCT III examination of macular diseases were developed. The first part contains basic advice for the OCT examination with respect to the examiner, patients, image quality, movement artefacts, algorithms, archiving and interpretation of OCT images. The second part consists of the relevance and indications for OCT examination especially in age-related macular degeneration (AMD), subgroups of AMD and follow-up after treatment. The third part demonstrates a brief outlook on future developments, such as the digital integration method (DIM), which provides identical scan localization in follow-up and eliminates any movement artefacts.

CONCLUSION

The application of standardized routine scanning and analysis protocols in Stratus OCT III for macular diseases and follow-up examinations provides an optimized, time-saving and comparable use of OCT. Therefore, the relevance and quality of OCT is increased for routine use in outpatient departments, hospitals and also for clinical studies.

Clinical use and research applications of Heidelberg retinal angiography and spectral-domain optical coherence tomography - a review

Fluorescein angiography (FA) was discovered by Nowotny and Alvis in the 1960s of the 20th century and has evolved to become the 'Gold standard' for macular diagnostics. Scanning laser imaging technology achieved enhancement of contrast and resolution. The combined Heidelberg retina angiograph (HRA2) adds novel innovative features to established fundus cameras. The principle of confocal scanning laser imaging provides a high resolution of retinal and choroidal vasculature with low light exposure providing comfort and safety for the patient. Enhanced contrast, details and image sharpness image are generated using confocality. For the visualization of the choroid an indocyanine green angiography (ICGA) is the most suitable application. The main indications for ICGA are age-related macular degeneration, choroidal polypoidal vasculopathy and choroidal haemangiomas. Simultaneous digital FA and ICGA images with three-dimensional resolution offer improved diagnosis of retinal and choroidal pathologies. High-speed ICGA dynamic imaging can identify feeder vessels and retinal choroidal anastomoses, ensuring safer treatment of choroidal neovascularization. Autofluorescence imaging and fundus reflectance imaging with blue and infrared light offer new follow-up parameters for retinal diseases. Finally, the real-time optical coherence tomography provides a new level of accuracy for assessment of the angiographic and morphological correlation. The combination of various macular diagnostic tools, such as infrared, blue reflectance, fundus autofluorescence, FA, ICGA and also spectral domain optical coherence tomography, lead to a better understanding and improved knowledge of macular diseases.