Abstract
Purpose: :
To describe the structural changes in the transition zone [1] from relatively healthy to severely affected regions in patients with RP using frequency domain optical coherence tomography (fdOCT).
Methods: :
FdOCT (Spectralis, Heidelberg) horizontal line scans of the midline were obtained from one eye of 13 patients with RP [x-linked (8), isolate (4), dominant (1)] and 30 control subjects. The patients had normal or near normal foveal sensitivities (≥32dB) and visual field diameters ≥10°. The thicknesses of the outer segments (OS), outer nuclear layer plus outer plexiform layer (ONL+), inner nuclear layer (INL), RGC plus inner plexiform (RGC+), and nerve fiber layer (RNFL) were measured with manual segmentation aided by a computer program.[2] For each patient, each layer, and each region (defined below), 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.
Results: :
The progression from healthy to severely affected regions followed a common pattern. Region A (6 eyes), the central region, had a normal or near normal OS (0.92±0.02) and ONL+ (0.95±0.04) thickness. Region B (9 eyes) had a significantly thinner OS (0.61±0.03), but a near normal ONL+ (0.88±0.03). All but one patient had regions A and/or B. Region C (all eyes) showed a further decrease in OS (0.38±0.02) with a decreased ONL+ (0.73±0.02). In Region D (11 eyes), the OS layer disappeared (0.00±0.00), as did the IS/OS line, while the ONL+ decreased further (0.55±0.03). In region E (12 eyes), the ONL+ was reduced to less than half the normal value (0.45±0.03). Finally, in more affected patients, the RPE was disrupted. The INL thickness was essentially normal throughout all regions (0.81±0.04 to 1.05±0.06). RNFL was often thicker beyond region A.[2]
Conclusions: :
The structural changes in the transition zone followed an orderly progression from thinning of OS to a loss of the ONL, although the extent of the regions varied across patients. Similar, but not identical, regions have been reported in patients with Usher type 1b.[1] It remains to be seen how this zone varies among RP genotypes and whether this approach offers a model of progression over time.1. Jacobson et al (2009) IOVS, 50, 1886; 2. Hood et al (2009) IOVS, 50, 4254.
Keywords: retinal degenerations: hereditary • retina • photoreceptors