IMPORTANCE Determining the annual rate of change in the width of the inner segment ellipsoid zone (EZ; ie, inner/outer segment border) in the context of short-term variability should allow us to better understand the value of this measure for future treatment trials in X-linked retinitis pigmentosa (XLRP).OBJECTIVES To identify the width of the central region showing an EZ and to determine the short-term repeat variability and the annual rate of change in the width of the EZ from spectral-domain optical coherence tomography (SD-OCT) measures in RP. DESIGN Patients with recessive or simplex RP (age range, 8-65 years; mean age, 40.5 years) underwent scanning twice on the same day to evaluate test-retest variability. Patients with XLRP (age range, 8-27 years; mean age, 15.2 years) from a larger group participating in an ongoing double-blind treatment trial (docosahexaenoic acid vs placebo; clinicaltrials.gov NCT00100230) underwent spectral-domain optical coherence tomography line scanning across the horizontal meridian at 3 yearly intervals. SETTING Research center specializing in medical retina. PARTICIPANTS Forty-eight patients with RP, including 20 with recessive or simplex RP and 28 with XLRP, and 23 healthy control subjects. MAIN OUTCOME AND MEASURE Widths of the EZ calculated and compared among the 3 annual visits.RESULTS Test-retest differences were normally distributed, and the magnitude of the difference was independent of mean EZ width. The mean (SD) for test-retest differences in EZ width was 0.08°(0.22°) (range, −0.30°to 0.60°). Thus, 95% of all test-retest differences fall within ±0.43°(124 μm). Of the 28 patients with XLRP, 27 showed a significant decrease in EZ width after 2 years. Patients with XLRP showed a mean annual decrease in EZ width of 0.86°(248 μm, or 7%). CONCLUSIONS AND RELEVANCEThe mean rate of decline in EZ width (7%) translates into a mean rate of change of 13% for the equivalent area of functioning retina. This rate of change is consistent with that reported for visual fields and full-field electroretinograms. Unlike visual fields and electroretinograms, however, the repeat variability is less than the annual rate of change. These results support the validity of EZ width as an outcome measure in prospective clinical trials in RP.

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SD-OCT provides a non-invasive method of following long-term retinal changes in mice in vivo. Although rd10 and rd1 mice have mutations in the same gene, they demonstrate significantly different features on SD-OCT.

Both rods and cones can support an intact IS/OS junction and normal photoreceptor thickness measures. The product of ONL and OS thicknesses is proportional to the sensitivity mediated by the less abnormal type of photoreceptor.

In patients with RP, preserved cone photoreceptor function measured by mfERG amplitude and visual field sensitivity correlate well with the remaining thickness of the photoreceptor layer. All three measures show comparable relative loss beyond 3° eccentricity. In the fovea, SD-OCT outer retina thickness showed less relative loss than either mfERG or visual field sensitivity.