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Rebecca Bausell, Rithambara Ramachandran, Cindy Cai, Kirsten Locke, David Birch, Donald Hood; Changes to the Transition Zone with Progression of X-Linked Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2013;54(15):665.
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A cross-sectional analysis of the transition zone (TZ), the region between healthy and severely affected retina, is thought to be a model of disease progression in patients with retinitis pigmentosa (RP).[1-4] Here we analyze TZ changes in a group of x-linked (xl)RP patients over time.
Two 9mm horizontal line scans, taken with optical coherence tomography, were obtained for one eye of 28 xlRP patients (15.2 ±6.1 yrs) at least 2 years apart (mean 2.4 yrs). Using a computer-aided manual procedure, outer segment (OS) and outer nuclear layer (ONL) thicknesses were measured. As previously described, to quantify changes across the fovea, the TZ was divided into regions A-E based upon the thicknesses of the OS and ONL relative to healthy controls. Region A: OS and ONL normal; B: OS reduced, ONL normal; C: OS and ONL reduced; D: ONL reduced, OS gone; E: ONL reduced to asymptotic thickness. We compared changes in the TZ regions between the first and last visit based upon: 1) location (distance from fovea) and 2) width. Region A was not analyzed as it was absent in 84% of patients. To determine changes in the TZ with eccentricity, patients were also placed in two groups based upon distance of the border between C and D (the point that OS disappears) from the fovea. Nasal and temporal measurements were averaged and paired t-tests were performed.
As expected, given the central progression of xlRP, the location of regions C (p=.054), D (p<.001) and E (p=.004) shifted towards the fovea (diagonal lines in Fig. 1). Concurrently, the widths of B and C decreased, while D and E expanded (Fig.1). At the final visit, the widths of B and C were narrower, while D and E were wider, in those with C/D borders closer, as compared to farther, from fixation (Fig. 2).
The TZ exhibits consistent changes with time. All borders move closer to the fovea, and the widths of regions (B & C) with the OS layer present decrease, while regions (D & E) without a detectable OS layer expand. Further, changes in the relative size of these regions with eccentricity are consistent with changes over time and support the TZ as a model of disease progression. 1. Jacobson et al. IOVS, 2009, 2. Jacobson et al. IOVS, 2010, 3. Hood et al. IOVS, 2011, 4. Lazow et al. IOVS, 2011.
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