Exploring How New Imaging Modalities Can Change Patient Care
BY JEFFREY S. HEIER, MD
We are in the midst of a retinal revolution, a time in which our approach to virtually every common retinal disease we treat is undergoing change. Advances have occurred in all aspects of disease management, including diagnosis, surgical technique and instrumentation, and pharmacologic treatments. We have 23-gauge and 25-gauge sutureless surgery with new instrumentation and light sources. We have new pharmacotherapeutics, such as agents that target vascular endothelial growth factor (anti-VEGF agents) and steroid implants.
Optical coherence tomography (OCT) has led to significant changes in our management of AMD and retinal diseases associated with edema. Some of these advances are being led by improvements in diagnostic imaging, and some of these advances are leading to improvements in diagnostic imaging. For example, OCT was predominantly a research tool until the success of treatment advances such as anti-VEGF and triamcinolone injections led to a realization of its benefits as a treatment-monitoring tool.
Now there is a new world of diagnostic imaging unfolding before us. Lasers and superluminescent diodes are changing the way we look at the eye, revealing new information and new ways of understanding the disease process.
What we knew as OCT is now changing into spectral domain OCT (also known as Fourier domain OCT). With this advancement, we are now able to resolve most of the layers of the eye, and debate has already begun on how these high resolution images correlate with histology.
IMPROVED FLUORESCEIN AND ICG ANGIOGRAPHY
Confocal scanning laser technology (cSLO) is providing us with a multitude of new imaging modalities. The cSLO enables us to excite fluorescein dye at its peak wavelength, returning images with finer detail than traditional photography, and providing movies of blood flow which tell a different story than intermittent still images.
Fig. 1. CNV that is missed by fluorescein is detected with a SD-OCT volume scan as well as with ICG angiography.
Fig. 2. In this case of central serous retinopathy, autofluorescence revealed much more extensive damage to the retinal pigment epithelium than fundus photography or fluorescein angiography, explaining the patient's count fingers visual acuity.
The improvement in angiographic image quality is most dramatic when applying cSLO to indocyanine green (ICG) imaging. While Yannuzzi and others showed us the first signs of RAP through cloudy images of the choroid, ICG imaging using cSLO provides clear views of the choroidal vasculature. In one of our cases, we used simultaneous ICGA with spectral domain OCT to find CNV that was not apparent on fluorescein angiography. We picked it up as little blip on an OCT scan and confirmed it with ICG (Figure 1).
AUTOFLUORESCENCE: IMAGING WITHOUT DYE
Another coming innovation is autofluorescence. This is the concept of using laser wavelengths to excite naturally occurring fluorophores in the retinal pigment epithelium (RPE) cells to obtain images without using any invasive dye. While autofluorescence is not a new imaging modality, it is one in which we are only beginning to understand and appreciate its potential.
Giovanni Staurenghi, MD, who has as much experience as anyone with autofluorescence, recently showed us early and late phase frames from angiograms in 6 different cases of age-related macular degeneration. In at least 2 (and most likely 3 or 4) of the cases, I would have treated what I thought was choroidal neovascularization (CNV). However, autofluorescence showed the lesions were not due to CNV, but were consistent with patterns of vitelliform disease.
In another case, I had been following a patient with a history of central serous chorioretinopathy for about 5 years (Figure 2). Fundus photography and fluorescein angiography both showed diffuse RPE changes, but the patient's acuity in the left eye was still less than that expected on these tests alone. However, using autofluorescence we could see that the RPE was extensively damaged.
Fig. 3. Wide field image captured with the Staurenghi contact lens combined with the Spectralis HRA+OCT.
Fig. 4. A dual beam imaging system can identify the precise location of pathology by using the simultaneous acquisition of a high quality fundus image combined with a SD-OCT cross section.
Combining fundus camera capabilities with laser imaging enables wide field images (Figure 3). We can obtain limited fields with all of our instruments and identify areas of pathology, but we can get a better feel for the case with a wider field. With wide field images, we can add important information to our findings, such as peripheral dropout.
Three dimensional volume scans allow us to evaluate the entire macula, and then mark the area in question with a baseline scan using any of 5 different modalities, in order to follow this exact area over time (Figure 4). Using eye tracking technology, both the fundus image and the selected cross-sectional scan can be followed automatically on a repeat exam, greatly enhancing our ability to detect and analyze abnormalities.
DOES NEW TECHNOLOGY ADD VALUE?
So now that we have the next generation of high resolution imaging, the real question is: what are the real benefits?. Do these beautiful new images really affect what we do in daily life and will they have an impact on our patients?
We have invited a group of panelists, experienced with the new imaging modalities to address these questions.
|Jeffrey S. Heier, MD, is a vitreoretinal surgeon at Ophthalmic Consultants of Boston and president of the Center for Eye Research and Education in Boston, Mass. He can be reached at firstname.lastname@example.org or (617) 314-2611.|