Reliability of a Manual Procedure for Marking the EZ Endpoint Location in Patients with Retinitis Pigmentosa

Rithambara Ramachandran, Cindy X Cai, Dongwon Lee, Benjamin C Epstein, Kirsten G Locke, David G Birch, Donald C Hood, Rithambara Ramachandran, Cindy X Cai, Dongwon Lee, Benjamin C Epstein, Kirsten G Locke, David G Birch, Donald C Hood

Abstract

Purpose: We developed and evaluated a training procedure for marking the endpoints of the ellipsoid zone (EZ), also known as the inner segment/outer segment (IS/OS) border, on frequency domain optical coherence tomography (fdOCT) scans from patients with retinitis pigmentosa (RP).

Methods: A manual for marking EZ endpoints was developed and used to train 2 inexperienced graders. After training, an experienced grader and the 2 trained graders marked the endpoints on fdOCT horizontal line scans through the macula from 45 patients with RP. They marked the endpoints on these same scans again 1 month later.

Results: Intragrader agreement was excellent. The intraclass correlation coefficient (ICC) was 0.99, the average difference of endpoint locations (19.6 μm) was close to 0 μm, and the 95% limits were between -284 and 323 μm, approximately ±1.1°. Intergrader agreement also was excellent. The ICC values were 0.98 (time 1) and 0.97 (time 2), the average difference among graders was close to zero, and the 95% limits of these differences was less than 350 μm, approximately 1.2°, for both test times.

Conclusions: While automated algorithms are becoming increasingly accurate, EZ endpoints still have to be verified manually and corrected when necessary. With training, the inter- and intragrader agreement of manually marked endpoints is excellent.

Translational relevance: For clinical studies, the EZ endpoints can be marked by hand if a training procedure, including a manual, is used. The endpoint confidence intervals, well under ±2.0°, are considerably smaller than the 6° spacing for the typically used static visual field.

Keywords: ellipsoid zone (EZ); optical coherence tomography; receptors; retinitis pigmentosa.

Conflict of interest statement

R. Ramachandran, None; C.X. Cai, None; D. Lee, None; B.C. Epstein, None; K.G. Locke, None; D.G. Birch, None; D.C. Hood, None

Figures

Figure 1
Figure 1
(A) Patient breakdown. (B) Horizontal midline fdOCT scan with three borders manually segmented. Inset: Enlargement of the region within the orange rectangle with EZ EP identified.
Figure 2
Figure 2
(A) Horizontal midline fdOCT scan with EP identified by graders A (red), B (blue), and C (green) at time 1. Inset: Enlargement of the region within the orange rectangle. (B) Horizontal midline fdOCT scan with EP identified by graders A (red), B (blue), and C (green) at time 2. Inset: Enlargement of the region within the orange rectangle.
Figure 3
Figure 3
(A) Scatterplot of EP markings at time 1 and time 2 for graders A (left), B (center), and C (right). Best-fit line and identity line are shown as the solid and the dashed line respectively. (B) Bland-Altman plot demonstrating agreement between EP markings at time 1 and time 2. EP, endpoint; ΔEPintra, measure of intragrader agreement.
Figure 4
Figure 4
(A) Scatterplot of EP markings of each grader (EPgrader) and the average marking of the other two graders (EPothers) at time 1. (B) Scatterplot of EP markings of each grader (EPgrader) and the average marking of the other two graders (EPothers) at time 2.
Figure 5
Figure 5
Plots of ΔEPinter as a function of the mean EPall at time 1 (A) and time 2 (B). EP, endpoint; ΔEPinter, measure of intergrader agreement.

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