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Cindy Xinji Cai, Kirsten G Locke, Rithambara Ramachandran, David G Birch, Donald C Hood; A Comparison of Progressive Loss of the Ellipsoid Zone (EZ) in Autosomal Dominant and X-linked Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1396.
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In patients with retinitis pigmentosa (RP), the EZ (aka ISe or IS/OS border) is a marker of the usable visual field at a given time and of disease progression over time.1,2 Here we compare the change in the width per year of the EZ in patients with autosomal dominant (ad) and x-linked (xl) RP.
Two 9 mm horizontal line scans through the fovea, taken with Spectralis HRA+OCT (Heidelberg Engineering, Vista, CA) using the eye-tracking feature (ART) and an average of 100 scans, were obtained for one eye of 33 adRP patients (mean age 53 yrs, range 11-71 yrs) at least 7 months apart (mean follow-up 2.01 yrs, range 0.63-4.8 yrs) and 28 xlRP patients (mean age 14.5 yrs, range 8-28 yrs; mean follow-up 2 yrs, range 1.91-2.3 yrs).2 For inclusion, eyes had to have a detectable EZ within the central 30°. Scans with EZ that were difficult to distinguish from the retinal pigment epithelium (RPE) were excluded (11 eyes), as were eyes without an abnormal EZ within the central 30° (4 eyes). When multiple scans were available, those with the clearest EZ were chosen. Using a manual segmentation procedure,3 the EZ was delineated and its width determined.
Unsurprisingly given the inclusion criteria, the adRP and xlRP patients had similar EZ widths at the initial visit (adRP: 12.40±6.30°, xlRP: 12.41±5.70°, p=0.99). However, the loss of EZ width over the mean 2 year follow-up was significantly greater (p<0.001) for xlRP (0.85±0.49°) than for adRP (0.37±0.55°) patients, as was the percent loss per year (p<0.001), 3.44±5.44%/yr (adRP) vs. 7.70±3.91%/yr (xlRP). There was a weak correlation between the loss of EZ width per year and the initial width for xlRP (r2=0.15, p=0.037), but no correlation for the adRP (r2=0.004, p=0.72).
While there is agreement that the onset of xlRP is typically earlier than most forms of adRP, there has been disagreement as to whether the yearly rates of disease progression are the same. The OCT data here support a faster rate of loss per year in the case of xlRP.4-5 1. Hood et al. Biomed Opt Express, 2011, 2. Birch et al. JAMA Ophthalmol, 2013, 3. Hood et al. Invest Ophthalmol Vis Sci, 2009, 4. Sandberg et al. Invest Ophthalmol Vis Sci, 2007, 5. Birch et al. Ophthalmology, 1999
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