As techniques of retinal imaging have evolved, anatomic features that were only assessable in the laboratory have become available in the clinic for patient care. The retinal capillaries were initially described on microscope sections in the pathology laboratory. As optical methods have advanced these features have become part of the routine clinical landscape inspected daily by physicians. This paper briefly traces the evolution of these techniques and shows how they fit into the modern diagnostic armamentarium of ophthalmic retinal care.
The authors report preliminary clinical results using an unique instrument which acquires and displays simultaneously an OCT image, a confocal image similar to that of a scanning laser ophthalmoscope and an indocyanine green fluorescence image. The three images are produced by three channels, an OCT and a confocal channel operating at 793 nm and a confocal channel tuned on the ICG fluorescence spectrum, which peaks at 835 nm. The system is based on our previously described ophthalmic Optical Coherence Tomography (OCT)/confocal imaging system, where the same source is used to produce the OCT image and excite fluorescence in the ICG dye. The system is compact and assembled on a chin rest and it enables the clinician to visualise the same area of the eye fundus in terms of both en-face OCT slices and ICG angiograms, displayed at the same time. The images are collected by fast T-scanning (en-face) which are then used to build B-scan or C-scan images.
By dividing both the object and reference beam in an OCT interferometer, two independent OCT imaging channels are assembled. The depth scanning proceeds simultaneously in the two OCT channels and from the same range, however a differential optical path difference can be introduced between the two channels. In this way, two simultaneous images are generated where the depth differs in each pixel by the differential optical path difference. A dual OCT system working at 850 nm was devised and we demonstrate the capability of the method by simultaneously acquiring images from the optic nerve and fovea of a volunteer. The configuration devised insures a strict pixel to pixel correspondence between the two images irrespective of the axial eye movements while the depth difference between the corresponding pixels is exactly the differential optical path difference. The images are collected by fast en-face scanning (T-scan) which allows both B-scan and C-scan acquisition.
En-face OCT acquired simultaneously with paired confocal ophthalmoscopic (CO) images provides unprecedented point-to-point correlation between surface and subsurface anatomy of the retina. An advanced prototype of a dual channel OCT/CO instrument was developed in terms of signal to noise ratio and image size. The system can operate in A, B and C-scan regimes. The design is such that there is a strict pixel to pixel correspondence between the OCT and confocal images. An extensive array of clinic pathologies were studied including macular degeneration, central serous retinopathy (CSR), macular hole, macular pucker, cystoid macular edema (CME), diabetic maculopathy, and macular trauma. We report observation of reoccurring patterns in the en-face OCT images which could be identified with different diseases. The system can also simultaneously produce en-face OCT and indocyanine green (ICG) fluorescence images where the same source is used to produce the OCT image and excite the ICG. The system is compact and assembled on a chin rest and it enables the clinician to visualise the same area of the eye fundus in terms of both en face OCT slices and ICG angiograms, displayed side by side. The images are collected by fast en-face scanning (T-scan) followed by slower scanning along a transverse direction and depth scanning. The system is capable of providing chosen OCT B-scans at selected points from the ICG image.