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Kirsten G. Locke, Kelly I. Locke, Yuquan Wen, Dennis R. Hoffman, Don C. Hood, David G. Birch; FdOCT Outer Segment Layer (OS) Measures of Progression Over a Two-year Interval in Patients With X-linked Retinitis Pigmentosa (XLRP). Invest. Ophthalmol. Vis. Sci. 2012;53(14):4573.
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FdOCT measures of structural changes in the outer segment layer have been hypothesized as possible outcome measures for clinical trials of RP.[1,2] To better understand these measures, we characterized the length of the inner segment ellipsoid (ISe) band (aka inner/outer segment border ) and calculated outer segment (OS) area in a group of XLRP patients followed for 2 years and evaluated the rate of disease progression.
28 patients (ages 8-27, mean 15.2 yrs), from a larger group participating in an ongoing double-blind treatment trial for XLRP patients (DHA vs. placebo; clinicaltrials.gov NCT00100230), had fdOCT line scans across the horizontal meridian (Spectralis, Heidelberg) at three yearly intervals (visits A, B, and C). Patients who were included had transition zones (TZs) between relatively healthy and diseased outer retina within the central 30°. All scans were captured with the aid of automatic registration to ensure identical scan placement. The OS layer was defined by the ISe and the proximal border of the RPE as delineated with a manual segmentation technique aided by a computer program. The nasal and temporal boundaries (TZb) of the TZ were defined as the locations where the width of the OS layer had declined to zero. The diameter of the intact OS layer was defined as the horizontal distance between the two TZb points in degrees. The OS area was determined from the radius and used in a repeated measures analysis of variance to evaluate the significance of progression between visits.
The analysis of variance showed a significant decrease in OS area over the two years (F=53.71, p=0.018). All 28 patients showed a decrease in OS area from visit A to B and from visit B to C. Average annual decline in the OS area was 14% (SD=6.5%). There was a significant negative relationship between the size of initial OS area and rate of progression, such that patients with larger areas showed lower percentage rates of change (r=-0.45, p=0.016).
By monitoring the area of the OS, it is possible to detect degenerative loss over one-year periods. The 14% average rate of change is consistent with the reported rate of change in visual fields and electroretinograms. The data suggest that the rate of progression varies with the size of the initial OS area.1. Locke et al. #4986, ARVO 2011; 2. Hood et al Biomed Opt. 2011; 3. Spaide & Curcio Retina, 2011; 4. Hoffman et al., AJO 2004.
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