A comparison of progressive loss of the ellipsoid zone (EZ) band in autosomal dominant and x-linked retinitis pigmentosa

Abstract

Purpose: In patients with retinitis pigmentosa (RP), the inner segment ellipsoid zone (EZ; also known as the inner segment/outer segment [IS/OS] border) is a marker of the usable visual field at a given point in time and of the progression of the disease over time. Here we compare the change in the width per year of the EZ band in patients with autosomal dominant (ad) and x-linked (xl) RP.

Methods: Using optical coherence tomography (OCT), 9-mm horizontal and vertical line scans through the fovea were obtained for one eye of 26 xlRP patients and 33 adRP patients. Scans were repeated on average 2.0 years later (range, 0.6-4.8 years). Using a manual segmentation procedure, the EZ band was delineated and its horizontal width (HW) and vertical width (VW) were determined.

Results: The adRP and xlRP patients had similar initial EZ HW (xlRP: 11.8 ± 5.4°, adRP: 12.4 ± 6.3°, P = 0.69) and VW (xlRP: 8.5 ± 4.9°, adRP: 11.4 ± 7.1°, P = 0.09). However, between visits the absolute loss and percent loss of the EZ width per year was significantly greater for xlRP than adRP for both HW (xlRP: 1.0 ± 0.6°/y, 9.6 ± 5.6%/y; adRP: 0.4 ± 0.5°/y, 3.4 ± 5.4%/y; P < 0.001) and VW (xlRP: 0.8 ± 0.8°/y, 9.2 ± 8.9%/y; adRP: 0.3 ± 0.5°/y, 4.2 ± 6.4%/y; P < 0.01). There was a weak correlation between the loss of EZ width per year and the initial width for xlRP (r(2) = 0.17, P = 0.036), but no correlation for adRP (r(2) = 0.004, P = 0.73). The test-retest difference of EZ HW was 0.2 ± 0.5°.

Conclusions: The OCT data here support a faster rate of loss per year in the case of xlRP. (ClinicalTrials.gov number, NCT00100230.).

Keywords: optical coherence tomography; progression; retinitis pigmentosa.

Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc.

Figures

Figure 1

Horizontal midline frequency domain optical coherence tomography scan through the fovea with two borders manually segmented. The HW of the EZ band is defined as the distance between the nasal and temporal end points (i.e., where the middle of the EZ band merges with the pRPE).

Figure 2

Scatter plots of the initial horizontal and vertical EZ widths for the adRP (blue) and xlRP (red) patients. Individuals are plotted as open circles, and the solid line is the best fitting linear line. The correlation for the two groups is as follows: xlRP r2 = 0.89, P < 0.0001; adRP r2 = 0.91, P < 0.0001.

Figure 3

The horizontal and vertical scans from an xlRP and adRP patient both with similar initial horizontal EZ width. Insets show higher magnification of the EZ band with endings marked. Dashed vertical yellow line indicates the end of the EZ band at the initial visit, while the solid yellow line is for the last visit. The percent loss of the EZ width per year for each patient is located in the upper left hand corner of each panel.

Figure 4

Loss per year (in percent) of the EZ band horizontal (a) and vertical (b) widths. Individuals are represented as open circles and the mean ± standard error as solid squares. The patients whose scans are shown in Figure 3 are represented as solid circles, Patient A as dark purple, and patient B as light purple.

Figure 5

Bland-Altman plot showing the difference in EZ width from repeat analysis as a function of mean EZ band width. Mean difference in EZ width (solid black line) and 95% limits of agreement (black dashed line) are shown. Difference of 0° is shown as a red dashed line.