Use of Optical Coherence Tomography in the Diagnosis and Management of Uveitis

Uveitis is a challenging disease. It represents a major cause of ocular morbidity worldwide. More than half of all patients with uveitis develop sight threatening complications related to their disease, and up to 35% of patients suffer severe visual impairment 1, 2. Uveitis and its complications are responsible for 5% to 10% of all causes of legal blindness in developed countries 1, 3. The causes of uveitis are numerous, and include infectious conditions, autoimmune diseases, trauma and tumors (masquerade syndrome). To develop an accurate differential diagnosis, clinicians must consider all available information, including the patient history, anatomic location of the inflammation (anterior or posterior), character (granulomatous vs. non granulomatous), laterality, and chronicity of inflammation. Moreover, diagnostic tools, such as fluorescein angiography (FA), indocyanine green angiography (ICG), optical coherence tomography (OCT) and ultrasound, play an important role in the diagnosis and in the management of the uveitis 4. Until recently, fluorescein FA was the primary imaging modality used to detect macular edema and other features related with uveitis like choroidal neovascularization and serous retinal detachment. Although FA is useful for determining the presence of vascular leakage, this technique does not provide any three-dimensional anatomic information about the retinal layers, the retinal pigment epithelium (RPE) or the choroid. The development of OCT makes it possible to have high-resolution cross-sectional images of the retina or optic nerve. OCT is now proven to be an effective noninvasive method in detecting pathologic features in uveitis and is rapidly gaining popularity as an ancillary exam. It may be used to assist in the diagnosis of uveitis and may be repeated safely during follow-up to monitor response to any intervention 5, 6. Recently, the introduction of spectral domain OCT (SDOCT) has improved image quality. Spectral domain, a type of fourier domain detection, uses a high-speed spectrometer to measure light echoes from all time delays simultaneously enhancing OCT capabilities. The reference mirror does not require mechanical scanning. Improved sensitivity enables dramatic improvements in sampling speed and signal-to-noise ratio 7, 8. SD detection, coupled with improvements in light sources, achieves axial scanning speeds of greater than 20,000 A-scans per second with an axial resolution of 3 μm to 7 μm in the eye. Consequently SDOCT has the advantage of detecting small changes in the morphology of the retinal layers and subretinal space, allowing for precise anatomic detection of microstructural changes that may corresponds to progression or regression of chorioretinal lesions or complications secondary to uveitis6. In addition, SDOCT is also used for anterior segment imaging where it may illustrate features of anterior uveitis and its complications. This review focuses on SDOCT imaging in uveitis. It will first review OCT imaging in anterior uveitis; then, it will describe the image features observed in the posterior uveitis. OCT and Anterior Uveitis Anterior segment optical coherence tomography (ASOCT) allows the visualization of various features of the anterior segment, including iris thickness, anterior chamber (AC) depth, the extent of anterior synechiae, iris bowing, and angle lesions. In vivo cross-sectional imaging of the anterior segment from ASOCT is particularly useful in the presence of corneal opacity and ocular inflammation, where it is often difficult to use slit-lamp biomicroscopy to visualize the anterior segment. It can serve as an non-invasive method for assessment of anterior uveitis and its complications 9, and can detect features of uveitis such as inflammatory cells, keratic precipitates (Figure 1A), fibrin (Figure 1B), and corneal edema (Figure 1C). In addition, positive posterior segment findings on OCT (e.g. increased macular thickness, retinal edema) can often reinforce anterior uveitis findings and may suggest its manifestation as part of a panuveitis associated with systemic illnesses such as sarcoidosis and Vogt-Koyanagi-Harada syndrome 9, 10. Figure 1 Representative ASOCT images show different features of anterior uveitis (A) Keratic precipitates (arrow) on ASOCT; (B) Fibrin deposition (arrow); (C) Corneal edema (arrow); (D) Inflammatory cells in the anterior chamber, visualized as hyperreflective ... Anterior Chamber Inflammatory Cells on ASOCT Lowder et al. 11 used a high-speed prototype SDOCT (2,000 A-scan/sec, 1.3 micron wavelength) to characterize inflammatory and pigmented cells in the anterior chamber (AC) as hyperreflective spots. In 28 non-granulomatous anterior uveitic eyes, a significant correlation was found between the cell count on OCT and the clinical grading from slit-lamp biomicroscopy. Similarly, a significant correlation was found between 6 eyes with pigmentary particles on OCT and clinical grading. Another study by Agarwal et al 12, inflammatory cells in the AC were visualized on ASOCT as hyperreflective spots (Figure 1D) in eyes compromised AC visualization secondary to corneal edema or opacity. In their study of 62 eyes with AC inflammation, 91.6% of eyes with corneal edema (n=12) had identifiable hyperreflective spots consistent with AC cells on ASOCT, which were manually counted and graded using the standardization of uveitis nomenclature (SUN) criteria. At the same time, keratic precipitates (Figure 1A) were seen in 12 eyes as discrete hyperreflective spots attached to the cornea endothelium, and fibrinous membrane (Figure 1B) were detected in 4 eyes in the papillary area or endothelium of the cornea.