A Comparison of Methods for Tracking Progression in X-Linked Retinitis Pigmentosa Using Frequency Domain OCT

To compare the efficacy of frequency domain optical coherence tomography (fdOCT)-derived outer retinal measures in tracking disease progression in x-linked (xl) retinitis pigmentosa (RP) patients.

Macular volume scans and line scans (Spectralis) were obtained from 27 xlRP patients (15.3 ± 6.4 years) at two visits approximately 2 years apart. Changes in average outer retinal layer thicknesses across the volume scan were compared to changes detected by measures derived from the edge of the inner segment ellipsoid zone (EZ) band, that is, where the EZ band (also known as inner segment/outer segment border) disappears. Repeatability was tested on an independent set of 18 RP patients (43.5 ± 18.0 years).

Average outer segment (OS) and outer nuclear layer (ONL) thickness showed marginally significant annual changes (P < 0.05), while total receptor (TR) thickness showed a greater change (P < 0.01). All measures derived from the edge of the EZ band significantly decreased (P < 0.01). Mean ± SD for test-retest differences in horizontal widths was 0.01 ± 0.06 mm.

Measures of the EZ band are more effective in detecting disease progression than are thickness measures. Given the similar effectiveness of line and volume scans, manually marking the EZ band edge on vertical and/or horizontal line scans can be useful in tracking progression.

Because disease progression in RP can be relatively slow, annual changes can be difficult to monitor during the course of a clinical trial. Here we suggest a quick, effective, and reliable method for detecting subtle changes.