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David G Birch, Kirsten G Locke, Martin Klein, Dianna K H Wheaton, Dennis R Hoffman, Donald C Hood; Annual decline in visual sensitivity at the edge of the OCT-defined ellipsoid zone (EZ) in patients with RPGR-mediated x-linked Retinitis Pigmentosa (xlRP). Invest. Ophthalmol. Vis. Sci. 2014;55(13):1398.
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The edge of the EZ (ellipsoid zone) in patients with RP indicates a transition zone between relatively healthy and relatively degenerate retina (Hood et al., IOVS, 2011). We recently reported (Birch et al., JAMA Ophthalmol, 2013) that the EZ provides a sensitive biomarker for progression in OCT. The purpose of the present study was to determine whether the decline in visual field sensitivity is greater when measured in the transition zone at the edge of the EZ than when measured at other locations in the visual field.
Measures were obtained from 44 patients (ages 8 to 30 yrs) with xlRP due to a mutation in the RPGR gene. Each patient had cone 31 Hz ERG amplitude > 1.0 μV at baseline. On five consecutive yearly visits, static perimetric fields were obtained with a Humphrey field analyzer. Beginning with the third visit, horizontal midline SD-OCT scans were obtained with a Heidelberg Spectralis HRA +OCT. Manual segmentation was aided by previously published routines (Hood et al, 2009). Based on the segmented scans, two nasal and two temporal field locations were selected for each patient. One nasal and temporal pair was just inside the EZ edge and the other was just outside the EZ edge. The rate of change at these locations was compared to the rates for the macula (5 points within central 10 degrees) and the mid-periphery (70 points between 10 and 30 degrees).
Sensitivity declined at the highest rate just inside (0.9 ± 0.1 dB/year; 19%) and just outside (0.9 ± 0.1 dB/year; 19%) the edge of the EZ. By comparison, sensitivity in the macula and mid-periphery declined significantly slower at rates of 0.4 ± 0.1 dB/year (9%; t=23.5, p<0.001) and 0.6 ± 0.07 dB/year (13%; t=14.1, p<0.001).
The annual loss of sensitivity was higher in the transition zone than elsewhere in the retina. These results suggest that OCT identification of the EZ in each patient may allow for the design of patient-specific visual fields to monitor disease progression in clinical trials.
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