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Margot A. Lazow, Donald C. Hood, David G. Birch; FdOCT Analysis Of The Transition Zone Between Healthy And Severely Affected Regions In Patients With Choroideremia. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4976.
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To describe the structural changes in the transition zone (TZ) from relatively healthy to severely affected regions in patients with choroideremia (CHM) using frequency domain optical coherence tomography (fdOCT) and to compare these TZs to those published previously  in patients with retinitis pigmentosa (RP).
FdOCT (Spectralis, Heidelberg) horizontal line scans of the midline were obtained from one eye of 7 patients with CHM (mean: 39.9 yrs) and 30 control subjects (mean: 35.7 yrs); all but one patient had foveal sensitivities >34dB. The thicknesses of the outer segments (OS), outer nuclear plus outer plexiform layer (ONL+), and retinal pigment epithelium (RPE) were measured with manual segmentation aided by a computer program. For each patient, each layer, and each region, 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. The central region, region I (present in 5 of the 7 eyes), had a normal or near normal OS (0.86±0.02) and ONL+ (1.23±0.05) thickness, but a significantly thinned RPE (0.79±0.05). Region II (all eyes) had a significantly thinned OS (0.54±0.04), but a near normal ONL+ (1.05+0.05); the RPE (0.74±0.04) was significantly thinned. In region III (all eyes), the OS layer (0.00+0.00) had disappeared, as did the inner segment (IS)/OS line; the RPE (0.64±0.03) was significantly thinned, but ONL+ (0.98±0.07) was still near normal. In region IV (all eyes), the outer limiting membrane (OLM) had disappeared; the outer plexiform layer had separated, forming an 'interlaminar bridge'; the ONL+ had became abnormal or undetectable; and RPE (0.54±0.02) was significantly thinned. The CHM TZ is largely consistent with the Jacobson et al model.
There are marked differences between the TZs in CHM and RP patients, both in RPE and ONL+ thickness. Whereas RPE thickness remains normal across the TZ in RP, the RPE in CHM may be thin in the otherwise healthy macula and is significantly thinned before the end of the TZ. While ONL+ loss occurs just beyond OS loss in RP, ONL+ thickness is preserved over a longer distance in the CHM TZ. This suggests that in CHM, unlike RP, cells bodies are able to survive for some time without a detectable OS layer. 1. Hood et al (2009) IOVS, 50, 2328; 2. Jacobson et al (2006) IOVS, 47, 4113; 3. Hood et al (2010) IOVS, 10, 5799.
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