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M. A. Lazow, D. C. Hood, K. G. Locke, V. C. Greenstein, D. G. Birch; FdOCT Analysis of the Transition Zone Between Healthy and Severely Affected Regions in Patients With Retinitis Pigmentosa (RP). Invest. Ophthalmol. Vis. Sci. 2010;51(13):1359.
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To describe the structural changes in the transition zone  from relatively healthy to severely affected regions in patients with RP using frequency domain optical coherence tomography (fdOCT).
FdOCT (Spectralis, Heidelberg) horizontal line scans of the midline were obtained from one eye of 13 patients with RP [x-linked (8), isolate (4), dominant (1)] and 30 control subjects. The patients had normal or near normal foveal sensitivities (≥32dB) and visual field diameters ≥10°. The thicknesses of the outer segments (OS), outer nuclear layer plus outer plexiform layer (ONL+), inner nuclear layer (INL), RGC plus inner plexiform (RGC+), and nerve fiber layer (RNFL) were measured with manual segmentation aided by a computer program. For each patient, each layer, and each region (defined below), the normalized thickness was the thickness divided by the mean control value. Numbers in parentheses are the mean (normalized thickness) ±1SE; 1.0 is a value equal to the control mean.
The progression from healthy to severely affected regions followed a common pattern. Region A (6 eyes), the central region, had a normal or near normal OS (0.92±0.02) and ONL+ (0.95±0.04) thickness. Region B (9 eyes) had a significantly thinner OS (0.61±0.03), but a near normal ONL+ (0.88±0.03). All but one patient had regions A and/or B. Region C (all eyes) showed a further decrease in OS (0.38±0.02) with a decreased ONL+ (0.73±0.02). In Region D (11 eyes), the OS layer disappeared (0.00±0.00), as did the IS/OS line, while the ONL+ decreased further (0.55±0.03). In region E (12 eyes), the ONL+ was reduced to less than half the normal value (0.45±0.03). Finally, in more affected patients, the RPE was disrupted. The INL thickness was essentially normal throughout all regions (0.81±0.04 to 1.05±0.06). RNFL was often thicker beyond region A.
The structural changes in the transition zone followed an orderly progression from thinning of OS to a loss of the ONL, although the extent of the regions varied across patients. Similar, but not identical, regions have been reported in patients with Usher type 1b. It remains to be seen how this zone varies among RP genotypes and whether this approach offers a model of progression over time.1. Jacobson et al (2009) IOVS, 50, 1886; 2. Hood et al (2009) IOVS, 50, 4254.
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