Baseline OCT measurements in the idiopathic intracranial hypertension treatment trial, part I: quality control, comparisons, and variability

Abstract

Purpose: Optical coherence tomography (OCT) has been used to investigate papilledema in single-site, mostly retrospective studies. We investigated whether spectral-domain OCT (SD-OCT), which provides thickness and volume measurements of the optic nerve head and retina, could reliably demonstrate structural changes due to papilledema in a prospective multisite clinical trial setting.

Methods: At entry, 126 subjects in the Idiopathic Intracranial Hypertension Treatment Trial (IIHTT) with mild visual field loss had optic disc and macular scans, using the Cirrus SD-OCT. Images were analyzed by using the proprietary commercial and custom 3D-segmentation algorithms to calculate retinal nerve fiber layer (RNFL), total retinal thickness (TRT), optic nerve head volume (ONHV), and retinal ganglion cell layer (GCL) thickness. We evaluated variability, with interocular comparison and correlation between results for both methods.

Results: The average RNFL thickness > 95% of normal controls in 90% of eyes and the RNFL, TRT, ONH height, and ONHV showed strong (r > 0.8) correlations for interocular comparisons. Variability for repeated testing of OCT parameters was low for both methods and intraclass correlations > 0.9 except for the proprietary GCL thickness. The proprietary algorithm-derived RNFL, TRT, and GCL thickness measurements had failure rates of 10%, 16%, and 20% for all eyes respectively, which were uncommon with 3D-segmentation-derived measurements. Only 7% of eyes had GCL thinning that was less than fifth percentile of normal age-matched control eyes by both methods.

Conclusions: Spectral-domain OCT provides reliable continuous variables and quantified assessment of structural alterations due to papilledema. (ClinicalTrials.gov number, NCT01003639.).

Keywords: OCT; intracranial hypertension; optical coherence tomography; papilledema.

Figure 1

High-definition five-line raster through the ONH showing the difficulty in including the entire vertical dimensions of the swollen optic disc. For each raster line, the ONH elevation was measured by manually placing a vertical line from a line connecting the RPE layer temporal and nasal neural canal borders to the top of the ONH.

Figure 2

Three-dimensional segmentation of the ONH region volume scan. Top: Actual axial images. Bottom: Images flattened to allow 3D segmentation. Red line defines internal limiting membrane. Yellow lines follow Bruch's membrane and RPE. Pink line defines the RNFL layer border.

Figure 3

Three dimensional segmentation compared to ZM calculations for average RNFL thickness.

Figure 4

Three-dimensional segmentation compared to ZM calculations for average TRT.

Figure 5

Three-dimensional segmentation compared to ZM calculations for average GCL+IPL thickness.