The Frisén scale, a photographic grading based upon descriptive features, has previously been the accepted method for diagnosing and monitoring papilledema. In a substudy of the NEI-funded Idiopathic Intracranial Hypertension Treatment Trial (IIHTT), researchers explored whether spectral-domain optical coherence tomography (SD-OCT) could provide a more precise, continuous measure for evaluating the disease.
A two-part study. The substudy findings were reported in two parts.1 Part I confirms that SD-OCT, using 3-D segmentation analysis, can reliably measure structural changes in the optic nerve head and peripapillary retina.
“OCT gave us a lot more information about the pathophysiological processes and changes with therapy than you would get just from a photo,” said lead author Mark K. Kupersmith, MD, professor of ophthalmology, neurology, and neurosurgery at the Icahn School of Medicine at Mount Sinai in New York City.
Part II focuses on correlating OCT findings with the clinical features of IIH.
Substudy methods. Using the Cirrus SD-OCT at 24 study sites, the researchers performed optic disc and macular scans in 126 subjects with mild visual field loss. They used both proprietary commercial and custom 3-D segmentation algorithms to calculate retinal nerve fiber layer and total retinal thickness, optic nerve head (ONH) volume, and retinal ganglion cell layer (GCL) thickness.
Analysis and artifacts. Standard SD-OCT imaging and software methods have limitations in measuring ONH swelling like that found in papilledema, said Dr. Kupersmith.
Problems can arise with both analysis and artifacts, the study found; conventional SD-OCT methods weren’t designed to evaluate disc edema when the normal architecture of retinal borders is obscured. Even when SD-OCTs acquire data correctly, the algorithms fail once swelling in the retina, ONH, or GCL passes a critical threshold.
A more reliable alternative. However, the 3-D segmentation algorithm, which incorporates contextual information, proved more reliable in evaluating retinal thickness, he said.
Correlations to clinical features. In Part II, the researchers studied the links between the imaging data and clinical features, such as acuity, visual fields, and low-contrast vision. As expected, they found a greater degree of swelling in patients with higher intracranial pressures. Further, all swelling parameters correlated well with the Frisén scale at baseline—though the correlation weakened as the disease progressed.
“Although early ganglion cell loss does correlate with a reduction in low-contrast vision,” he said, “we found few other correlations in this group of subjects with mild vision loss.” Nevertheless, this study validates the use of an alternative method to obtain credible data in papilledema.
1 Kupersmith MK; OCT Sub-Study Committee for the NORDIC Idiopathic Intracranial Hypertension Study Group. Invest Ophthalmol Vis Sci. Published online Nov. 4, 2014. Part I, doi:10.1167/iovs.14-14960; Part II, doi:10.1167/iovs.14-14961.
Dr. Kupersmith reports no related financial interests. The study received support from the National Eye Institute.
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