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D. G. Birch, K. G. Locke, H. Patel, W. Tao; Intraocular Sustained Release of CNTF Affects fdOCT Measures of Photoreceptor Function in Patients With Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4788.
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One-year outcome data was recently reported for a multi-center, randomized, double-masked, placebo-controlled clinical trial of ciliary neurotrophic factor (CNTF) in patients with retinitis pigmentosa. In a dose-dependent fashion, patients receiving an encapsulated cell implant secreting CNTF showed greater macular thickness on OCT3 (Zeiss Stratus OCT3) than at baseline. No change in thickness was seen in the sham treated eye. The goal of the present study is to utilize fourier domain (fd)OCT to explore the cause of the thickening.
All patients implanted at the Dallas site (n=28) consented to participate in the study. The fellow eye of each patient received a sham treatment and served as control. A horizontal scan from the midline of each eye was obtained with fdOCT (Heidelberg Spectralis HRA+OCT). Because the system was not available at baseline, we were unable to compare pre- and post-treatment. Therefore, we compared parameters between the CNTF-treated and sham-treated fellow eyes. To avoid areas with possible CME, we limited the analysis to the average of values obtained from 6 degrees (1.7 mm) nasal and temporal to the fovea.
Total retinal thickness at 6 degrees eccentricity was significantly greater in the treated eyes than the sham-treated fellow eyes (t=4.17; p< 0.001). Segmentation revealed that the thickening was due primarily to a difference in the width of the outer nuclear layer (ONL) The mean±se for treated eyes was 50.9±3.7 microns compared to sham 43.3±5 microns (t=3.57, p=0.001). No significant differences were found in the thickness of the outer segment/RPE layer for either group.
Previous results have shown that CNTF leads to retinal thickening compared to baseline in patients with RP. The present study expands this finding by showing that the thickening is also evident in a comparison of the treated with the untreated eye. The thickening does not appear to be due to an increase in the thickness of the OS-RPE layer, consistent with a lack of functional benefit at one year. The thickening seen in the ONL of the treated eye is consistent with the altered nuclear morphology seen in CNTF-treated animal models (Bush, IOVS, 2004) and suggests enhanced transcriptional activity. It remains to be determined whether these structural changes presage a functional benefit for patients over a longer treatment duration.
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