CLINICAL SCIENCES Simultaneous Indocyanine Green and Fluorescein Angiography Using a Confocal Scanning Laser Ophthalmoscope William R. Freeman, MD; Dirk-Uwe Bartsch, PhD; Arthur J. Mueller, MD, PhD; Alay S. Banker, MD; Robert N. Weinreb, MD Background: Fluorescein and indocyanine green (ICG) performed in 45 minutes. It was possible to study dif- angiography are both useful in the diagnosis and treat- ferences in fluorescein patterns by comparing identi- ment of many retinal diseases. In some cases, both tests cally timed frames and to find cases in which ICG or fluo- must be performed for diagnosis and treatment; how- rescein was optimal in visualizing retinal and subretinal ever, performing both is time-consuming and may re- structures. Confocal optical sections in the depth (z) di- quire multiple injections. mension allowed viewing in different planes. It was pos- sible to overlay ICG and fluorescein images or compare Methods: We designed a compact digital confocal scan- them side-by-side using a linked cursor. Digital trans- ning laser ophthalmoscope to perform true simulta- mission of the images was also performed. neous fluorescein and ICG angiography. We report our experience using the instrument to perform 169 angio- Conclusions: Simultaneous ICG and fluorescein angi- grams in 117 patients. ography can be performed rapidly, safely, and conve- niently. The availability of simultaneous angiography will Results: There were no unexpected adverse effects from allow critical determination of the relative advantages and mixing the dyes and administering them in 1 injection. disadvantages of both types of angiography. An entire examination, including fundus photography, fluorescein angiography, and ICG angiography, could be Arch Ophthalmol. 1998;116:455-463 LUORESCEIN angiography is a phy. This has made ICG angiography a useful tool for the diagnosis useful clinical diagnostic tool, particu- of many retinal diseases. It larly for imaging of subretinal neovascu- provides diagnostic as well as lar membranes in cases where such mem- treatment information by al- branes can not be adequately imaged with Flowing visualization of the retinal and cho- fluorescein angiography.4-8 roidal vasculature. Angiography allows identification of leakage of the small fluo- For editorial comment rescein molecule in pathological states. More recently, indocyanine green (ICG) see page 521 angiography has been developed. This molecule is larger (molecular weight, 775 Another approach to fluorescence an- d vs 332 d for fluorescein) and more pro- giography (using either fluorescein or ICG) tein-bound in plasma than is fluorescein is the scanning laser ophthalmoscope.9 This and fluoresces in the infrared spectrum. instrument has come into common clini- Initially, ICG angiography was per- cal practice because of its commercializa- formed with infrared photographic film. tion in recent years.10 Advantages of the However, the poor sensitivity of film scanning laser ophthalmoscope include the coupled with the relatively weak fluores- ability to use an excitation light that scans cence properties of the dye caused this the retina, allowing more intense excita- method to be abandoned.1-3 The strong tion (thus providing a stronger emission sig- binding of ICG dye to plasma proteins re- nal) while still using safe levels of illumi- sults in slow leakage as compared with nation. This is possible because the From the Department of fluorescein and reduces the amount of ex- scanning beam illuminates each area point Ophthalmology, Shiley Eye travascular fluorescence available for im- of the retina for only 0.1 to 0.7 microsec- Center, University of aging. Digital video cameras have been onds. Scanning laser ophthalmoscope an- California, San Diego. used to capture images for ICG angiogra- giography gives temporal information that ARCH OPHTHALMOL / VOL 116, APR 1998 455 ©1998 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/23/2021 MATERIALS AND METHODS PATIENT EXAMINATIONS We performed 169 angiograms in 117 patients with age- We used a confocal scanning laser ophthalmoscope with related macular degeneration, ocular melanoma, and other 2 laser light sources to illuminate the retina (Heidelberg retinal diseases. The patients were studied after a complete Retina Angiograph, Heidelberg Engineering Inc, Carls- ophthalmic examination that included fundus photogra- bad, Calif). The instrument uses 2 lasers with 3 wave- phy, slitlamp examination, and indirect ophthalmoscopy. We lengths as light sources for scanning fundus illumination. injected 2 mL of a mixture of 25 mg of ICG and 500 mg of An argon-ion laser (488 nm and 514 nm wavelength) was sodium fluorescein intravenously. This was prepared using used to provide red-free photographs (green, 514 nm) and sterile commercially available dyes suitable for intravenous blue light was used for excitation during fluorescein an- injection. The liquid sodium fluorescein (25% solution in 2 giograms (blue, 488 nm). The second laser was a diode la- mL; Fluorescite, Alcon, Fort Worth, Tex) was placed into a ser (795 nm wavelength) that provided illumination to ex- vial containing sterile ICG powder (CardioGreen, Becton cite the ICG dye, which fluoresces at 835 nm. The Dickinson, Cockeyville, Md) and the ICG was dissolved in instrument was operated in a tight confocal imaging mode the liquid fluorescein. No precipitates were seen. This re- and acquired up to 12 simultaneous frame pairs per sec- sulted in a sterile solution containing 25 mg of ICG and 500 ond. For each video line of the angiogram, the forward scan mg of sodium fluorescein. The patients underwent imaging was used for one angiogram and the backward scan was in the early phase (0-2 minutes after injection), the mid phase used for the other angiogram. Thus, the time separation (3-5 minutes for sodium fluorescein, 3-15 minutes for ICG), between corresponding lines of the 2 angiograms was on and late phase (10-12 minutes for sodium fluorescein, 40-45 the order of 0.1 milliseconds; each frame pair was ac- minutes for ICG). All patients were informed as to the risk quired in 0.08 seconds. The instrument allowed acquisi- and benefit factors of all procedures. The images were ana- tion of 12 frame pairs per second with 256 3 256 pixel and lyzed by 2 ophthalmologists (W.R.F. and A.J.M.). 8 bit per pixel intensity quantitation. The images were recorded in the confocal mode12,16,17,18 IMAGE STORAGE AND RETRIEVAL while the photographer moved the plane of focus in the depth (z) dimension during the angiogram to optimally im- The images were stored digitally in the RAM of the com- age the structures of interest. The chromatic aberration of puter during acquisition and subsequently transferred onto the human eye caused a 1-diopter (D) focus shift between the hard disk. The still frames of a typical angiogram se- the blue-green fluorescein angiogram image plane and the quence (n=50 frames) required 3.2 megabytes of hard disk infrared ICG angiogram image plane. The photographer se- memory. Video sequences (20 frames per second) re- lected a focal plane that allowed in-focus imaging of the quired 13 megabytes for each 10-second sequence of video. retinal vasculature in the fluorescein angiogram, which Using 40 megabytes of RAM, we allowed 30 seconds of live placed the ICG image plane 300 µm deeper in the retina video storage before moving the data to permanent hard and choroid. disk storage. is richer than still (“digital”) imaging systems because true mark”) injection of ICG dye.5 This instrument was the video allows imaging at rates of 20 to 30 frames per sec- first completely digital instrument to allow scanning la- ond. This allows more detail to be seen in the transit phases ser video angiography. Image capture and processing is and may give better information about patterns of leak- done digitally so that no information is lost at any stage ing vessels. Furthermore, the illuminating beam is mono- of processing, image manipulation, or transmission. chromatic and the intensity of fluorescence may be higher Although ICG angiography may be advantageous in because of the scanning laser ophthalmoscope beam and certain cases of subretinal neovascularization and in di- the fact that point-by-point illumination is used.10 Stereo- agnosing other disorders,4,5,7 one of its drawbacks is the scopic imaging is also possible using scanning laser oph- long period of time required for angiography (45 min- thalmoscope techniques.11 utes) and the need to obtain a second angiogram after a We recently described the use of a confocal scan- fluorescein angiogram is obtained. The process of ob- ning laser ophthalmoscope to perform tomographic im- taining a fluorescein and ICG angiogram sequentially is aging of macular diseases.12 By optically isolating the im- time consuming and requires 2 or 3 (if a landmark in- age plane to a narrow plane in the depth (z) dimension, jection is used) injections for each patient for comple- depth information and measurements could be ob- tion of the set of studies. Moreover, the angiograms are tained. Subsequently, we adapted the scanning laser to- performed at different times, making it difficult to know mograph to perform ICG angiography.13,14 The instru- if differences in fluorescence leakage patterns are due to ment allowed better discrimination against out-of-focus differences in properties of the dyes or in the quality of objects (tomography) and provided higher contrast than the photographs. This may be one