SD/SS-OCT (Heidelberg, Zeiss, Topcon)
Angiography (fluorescein, indocyanine green)
OCT-Angiography (Angiovue, Topcon, SS-OCTA)
OCT (optical coherence tomography)
Optical coherence tomography is a non-invasive imaging technique for acquiring 3D cross sectional scans of the retina. Starting in the early 1990’s, the development of the OCT technology has steadily improved over the last decades to become a standard in the field of clinical diagnosis and therapy of eye diseases. During an OCT examination, the instrument emits a light beam of a specific wavelength into the eye of the patient. The beam is reflected by the different layers of the neurosensory retina, the retinal pigment epithelium (RPE) and choroidal layers. A computer connected to the OCT console calculates the images in respect to the different layers of the retina. An OCT scan displays pathologic characteristics like drusen, intraretinal fluids, cysts, loss of pigment epithelium (geographic atrophy) and multiple other morphological biomarkers which are highly associated with leading retinal diseases such as age-related macular degeneration (AMD) in addition, diabetic retinopathies and vascular occlusive disease.
CF (color fundus photography)
Fundus photography is an imaging modality with the purpose of capturing photographs of the posterior pole of the eye. A combination of a special microscope and a digital camera provides the necessary platform. The camera can be additionally equipped with a variety of colored image filters. The field of view of the captured area is depending on the microscope and typically ranges from 20° up to 60°. In fundus photography mono- and stereo-images can be acquired with either 3 or 7 fields. The patient's pupil has to be dilated before an operator can acquire optimal fundus images. The strength of fundus photography lies in the detection of hemorrhages, fibrosis, geographic atrophy, drusen and many more pathologies associated with AMD and diabetic retinopathy.
FA (fluorescein angiography)
For fluorescein angiography, a fluorescent dye is injected into the cubital vein. After the injection, images are taken at defined moments of time to track the distribution of dye in the vasculature of the retina. A flash is emitted through a specific image filter into the patient's eye and excites the fluorescent particles of the dye. The distribution of the dye begins within the retinal arteries a few seconds after the injection, followed by filling of the arterioles and the capillary vessels (early arteriovenous phase). In the late arteriovenous phase, the dye reaches the retinal veins. A healthy eye shows a consistent distribution of the dye through all phases reflected by a normal level of fluorescence of the vessels. The level of fluorescence changes with different pathologies. hypo-fluorescence occurs when the flow in the vessels is blocked. Hyper-fluorescence occurs when fluorescent particles accumulate in an area, for example through leakage and staining of fluorescein. Fluorescein angiography is an established standard method to detect a wide range of pathologies that are linked with AMD and diabetic retinopathies.
FAF (fundus autofluorescence)
Fundus auto-fluorescence is a method in clinical imaging that can detect early stages of geographic atrophy by using the fluorescent properties of specific elements of the retinal layers, mainly lipofuscin, which is a product of the decomposition of photoreceptor cells and that is aggregated over the years in the retinal pigment epithelium. When excited by light, lipofuscin produces auto-fluorescence. Areas with accumulated lipofuscin appear therefore hyper-fluorescent on images captured by the fundus camera. Areas where RPE cells are lost (e.g. in geographic atrophy) in contrast present hypo-fluorescent on the images.