Optical coherence tomography in papilledema: what am I missing?

BACKGROUND: Grading of papilledema severity is subjective and based on monocular fundus features of the optic nerve. Interobserver agreement on grading the severity of papilledema is poor among expert observers, even using well-defined criteria such as the Frisen scale, which is a non-continuous ordinal scale of grading. Furthermore, non-expert clinicians often find it difficult to properly view and interpret features of the optic nerve using ophthalmoscopy, which can lead to failure to diagnose papilledema in non-ophthalmologic care settings. This may delay treatment, which can result in vision loss. Distinguishing papilledema from pseudopapilledema can also be difficult when surface drusen are not easily identified. Once papilledema is diagnosed, it is often difficult to determine whether a reduction in optic nerve edema is due solely to improvement in the status of the nerve or whether this represents concomitant loss of axons and viable retinal ganglion cells, leading to a poor visual outcome. Timely advancement of treatment would occur if loss of neurons could be diagnosed at an earlier stage of evaluation while optic disc edema is still present. This review will critically assess the role of optical coherence tomography (OCT) in solving these problems by providing an advanced imaging approach for diagnosis of papilledema and evaluating its severity on a continuous scale and evaluating the causes of visual loss in the setting of a swollen nerve. METHODS ACQUISITION: The published literature (PubMed) was reviewed from 2000 to 2014 on the use of OCT for diagnosing papilledema, differentiating it from pseudopapilledema, providing a continuous scale of its severity and in evaluating causes of visual loss.
RESULTS: Recent evidence shows that OCT analysis of the retinal nerve fiber layer and retinal ganglion cell layer in papilledema can be associated with misleading artifacts due to layer segmentation failures. Newer 3D algorithms using neighboring locations help to overcome these problems. Disc volume appears to be a promising continuous measure of papilledema that is robust and has less associated artifacts. Buried optic disc drusen can be identified using enhanced depth OCT imaging, but recent studies have shown poor ability to differentiate papilledema from pseudopapilledema using OCT when the degree of disc evaluation is similar. Analysis of the retinal ganglion cell layer shows promise of early detection of vision loss due to neuronal injury. Subretinal fluid is easily identified with OCT and can help to identify a potentially reversible component of vision loss. Newer OCT imaging methods will allow the definition of capillaries and flow within them in and around the optic nerve head.
CONCLUSIONS: Currently, the most useful OCT derived features relevant to papilledema are disc volume, subretinal fluid, buried disc drusen, and thickness of the retinal ganglion cell layer.