Abstract
Purpose.:
To develop an automated method for the quantification of volumetric optic disc swelling in papilledema subjects using spectral-domain optical coherence tomography (SD-OCT) and to determine the extent that such volumetric measurements correlate with Frisén scale grades (from fundus photographs) and two-dimensional (2-D) peripapillary retinal nerve fiber layer (RNFL) and total retinal (TR) thickness measurements from SD-OCT.
Methods.:
A custom image-analysis algorithm was developed to obtain peripapillary circular RNFL thickness, TR thickness, and TR volume measurements from SD-OCT volumes of subjects with papilledema. In addition, peripapillary RNFL thickness measures from the commercially available Zeiss SD-OCT machine were obtained. Expert Frisén scale grades were independently obtained from corresponding fundus photographs.
Results.:
In 71 SD-OCT scans, the mean (± standard deviation) resulting TR volumes for Frisén scale 0 to scale 4 were 11.36 ± 0.56, 12.53 ± 1.21, 14.42 ± 2.11, 17.48 ± 2.63, and 21.81 ± 3.16 mm3, respectively. The Spearman's rank correlation coefficient was 0.737. Using 55 eyes with valid Zeiss RNFL measurements, Pearson's correlation coefficient (r) between the TR volume and the custom algorithm's TR thickness, the custom algorithm's RNFL thickness, and Zeiss' RNFL thickness was 0.980, 0.929, and 0.946, respectively. Between Zeiss' RNFL and the custom algorithm's RNFL, and the study's TR thickness, r was 0.901 and 0.961, respectively.
Conclusions.:
Volumetric measurements of the degree of disc swelling in subjects with papilledema can be obtained from SD-OCT volumes, with the mean volume appearing to be roughly linearly related to the Frisén scale grade. Using such an approach can provide a more continuous, objective, and robust means for assessing the degree of disc swelling compared with presently available approaches.
In this retrospective study, patients with elevated intracranial pressure and papilledema at initial presentation to the neuro-ophthalmology clinic at the University of Iowa Hospitals and Clinics were included if they had undergone digital fundus photography and OCT (Cirrus; Carl Zeiss Meditec, Dublin, CA) disc scans at the same visit, and all subjects had been imaged at least twice on different dates. Fundus photographs were obtained with a retinal camera (RC50-DX; Topcon, Tokyo, Japan) with a 6-megapixel back (MegaVision, Santa Barbara, CA; 2392 × 2048 actual image size), which is a full-size (35 mm) CCD sensor (OIS, Sacramento, CA). Each SD-OCT scan had dimensions of 200 × 200 × 1024 voxels (6 × 6 × 2 mm3), with a voxel depth of 8 bits in grayscale. SD-OCT scans were excluded if the internal limiting membrane (ILM) or the RPE complex went outside the confines of the volume (z-axis) window of the scan. This sometimes occurs with greater severity of papilledema in which it can become more difficult for the OCT scan operator to include the entire height of the elevated optic nerve within the z-axis measurement window. The study protocol was approved by the University of Iowa's Institutional Review Board and adhered to the tenets of the Declaration of Helsinki. Because of its retrospective nature, informed consent was not required from subjects.
Correlation of Volumetric Parameters with 2-D Parameters and “Winner-Take-All” Expert Frisén Grades