Many recent advances in retinal imaging have augmented our ability to diagnose and manage retinal conditions. In this article, we review these modalities and how they help us to manage patients.
To determine what’s wrong with the retina, we have to visualize it. Performing a dilated funduscopic examination is sometimes challenging, such as in children, small pupils or uncooperative patients. We frequently supplement examination with fundus photography. This facilitates visualization and diagnosis. A record of photographs from prior visits helps us to manage patients longitudinally.
Fundus photography is the oldest retinal imaging modality, but there have been many recent innovations. Historically, fundus photographs had a limited field of view, so only small portions of the retina were captured in each image (Figure 1A). Newer modalities such as widefield (WF) and ultra-widefield (UWF) imaging enables us to visualize most of the retina in a single image (Figure 1B), though the fine details may be more difficult to discern. Many retinal diseases involve the peripheral retina, so being able to image these areas is essential.
In the clinic, we image patients with either UWF (Figure 2A) or WF cameras when we wish to capture the macula and most of the peripheral retina. If there is focused macular pathology, we utilize WF, occasionally asking our photographers to make montages of multiple photos throughout the posterior pole.
In addition, we use the Retcam instrument (Natus Newborn Care, Inc.) in the NICU and with babies. Also, we use Retcam in older children during examinations under anesthesia, or EUAs.
FLUORESCEIN ANGIOGRAPHY (FA)
FA entails intravenous cannulation and injection of a dye that fluoresces at a specific wavelength as it travels through the ocular circulation and tissues. FA highlights the retinal vessels and sites of pathology, such as retinal ischemia or neovascularization. These features are sometimes difficult or impossible to identify or delineate with examination or photography alone. Important considerations in performing FA include patient age and the type of camera used.
We utilize UWF (Figure 2B) unless we have previously demonstrated that there is no peripheral pathology and we are diagnosing or following macular disease, such as choroidal neovascularization, in which we use a WF platform. Sometimes we repeat FAs serially, such as to follow the progression of peripheral ischemia in Coats disease and guide targeted laser ablation to ischemic areas. Rarely, such as for posterior uveitis or polypoidal choroidal vasculopathy, we perform indocyanine green angiography simultaneously with FA.
OPTICAL COHERENCE TOMOGRAPHY
OCT technology measures the reflectivity of ocular tissues to create cross-sectional visualizations of the retina. Rapid, non-invasive and inexpensive, it provides high-resolution data regarding anatomical disruptions of various retinal diseases. We perform OCT on almost every patient. For example, we follow the progression of subretinal vitelliform material to atrophy in Best disease using OCT (Figure 3). During vitreoretinal surgery, we use microscope-integrated OCT to facilitate challenging surgical maneuvers, such as removal of epiretinal membranes or for subretinal injection for gene therapy.
FUNDUS AUTOFLUORESCENCE (FAF)
FAF uses filters for specific wavelengths of light to image the autofluorescence of the retinal pigment epithelium (RPE) and of some pathologic retinal lesions. The flash of light with FAF is brighter than that of fundus photography, so it can be more uncomfortable for patients. We typically reserve FAF imaging for situations of diagnostic uncertainty, such as in the diagnosis of central serous retinopathy or inherited retinal dystrophies (IRDs). For example, in Stargardt’s disease FAF often reveals many hyperautofluorescent flecks that are not visualizable on examination or photographs. FAF imaging can also provide insight into the health of the RPE in patients who will not tolerate FA.
We utilize ultrasound routinely. This technique is particularly helpful in cases of media opacity or retinal disorganization. For example, we find it particularly useful to diagnose retinal tears or detachments in cases of vitreous hemorrhage and to assess the anatomy of the posterior segment in patients with severe cataract (Figure 4).
OTHER IMAGING MODALITIES
OCT angiography (OCTA) is a newer technique that utilizes repeated OCT scans and imputes the presence of blood flow based on variable reflectivity within ocular tissues. Current OCTA instruments have a limited peripheral field of view, but this is changing rapidly with WF swept-source OCTA technologies (Figure 5). OCTA image acquisition requires longer periods of fixation than FA, so FA can be better in patients with poor fixation or poor cooperation. With wider fields of view and more rapid acquisition, OCTA may eventually replace FA.
For IRDs, we sometimes obtain electroretinograms. However, the results of multimodal imaging along with commercially available genetic testing are usually adequate for diagnosis and management. We rarely obtain electrooculograms or visual-evoked potentials. Visual fields are helpful to our colleagues who manage glaucoma that often accompanies retinal conditions.
These imaging modalities are essential to diagnosis and management of retinal disorders. It is also critical to have well-trained photographers and to communicate with them constantly. Newer imaging modalities are in development that may further enhance our ability to care for patients with retinal disease. OM