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Kirsten G. Locke, Kelly I. Locke, Yuquan Wen, Donald C. Hood, Dennis R. Hoffman, David G. Birch; FdOCT Measures Of Progression Over A One Year Interval In Patients With X-linked Retinitis Pigmentosa (XLRP). Invest. Ophthalmol. Vis. Sci. 2011;52(14):4986.
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Treatment trials for RP are complicated by the inherent variability of functional measures and the slow rate of progression. Thus, clinical trials require large numbers of patients and/or many years of follow-up. We have shown recently that there is close relationship between visual field sensitivity and frequency domain optical coherence tomography (fdOCT) measures of outer retinal thickness (Rangaswamy et al. IOVS, 2010). Here we evaluate progression over one year in the transitional zone (TZ) from relative healthy to severely affected retina.
25 patients (ages 8-34, mean 15.2 yr), from a larger group participating in an ongoing double-blind treatment trial for XLRP patients (DHA vs. placebo; ClinicalTrials.gov NCT00100230), had fdOCT horizontal line scans (Spectralis, Heidelberg) obtained 1 year apart. To be included, patients needed scans of high quality, with measurable outer segments across a TZ within 15° of the fovea, and from two annual visits captured with the aid of automatic registration to ensure identical scan placement. Patients with CME in the outer retinal layers were excluded. OS+ (from choroid to outer segment/inner segment border) and REC+ (from choroid to inner nuclear layer border) thicknesses were measured with manual segmentation aided by a computer program (Hood et al., IOVS, 2009). Diameters on the horizontal scan were defined for each patient where OS+ and REC+ thickness reached an asymptotically small value (Hood et al., IOVS, 2010). A paired t-test was used to evaluate possible changes in the OS+ and REC+ diameters between year 1 and 2.
Of the 25 patients, 24 showed a constricted diameter of measurable OS+ and 20 showed a constriction of REC+ on the year 2 scan as compared to year 1. One patient had no change in either OS+ or REC+. Four patients showed no change in only REC+ layer. The mean diameter of TZ in all XLRP patients for year 1 was 14.7° for OS+ and 21.4° for REC+. By year 2, average diameter of OS+ was reduced by 8% to 13.5° (p<0.001) and REC+ was reduced by 4% to 20.6° (p=0.003).
This method of monitoring the transition zone of the outer retina is capable of detecting degenerative loss over a relative short period of one year in young patients with XLRP. The result supports the use of fdOCT as outcome measure in future clinical trials.
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