A Comparison of Progressive Loss of the Ellipsoid Zone (EZ) Band in Autosomal Dominant and X-Linked Retinitis Pigmentosa

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 degrees, adRP: 12.4 +/- 6.3 degrees, P = 0.69) and VW (xlRP: 8.5 +/- 4.9 degrees, adRP: 11.4 +/- 7.1 degrees, 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 degrees/y, 9.6 +/- 5.6%/y; adRP: 0.4 +/- 0.5 degrees/y, 3.4 +/- 5.4%/y; P < 0.001) and VW (xlRP: 0.8 +/- 0.8 degrees/y, 9.2 +/- 8.9%/y; adRP: 0.3 +/- 0.5 degrees/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 degrees. CONCLUSIONS. The OCT data here support a faster rate of loss per year in the case of xlRP.