Evaluation of multimodal imaging in carriers of X-linked retinitis pigmentosa

Abstract

The aim of this study was to investigate visualization of the tapetal-like reflex using current imaging modalities and evaluate SD-OCT changes in known carriers of X-linked retinitis pigmentosa (XLRP); the objective being the development of an optimal protocol for clinicians to identify carriers. Ten XLRP carriers (19 eyes) were examined using color fundus photography, 488 nm reflectance (488-R), near-infrared reflectance (NIR-R), autofluorescence (AF) and spectral domain optical coherence tomography (SD-OCT) imaging (Spectralis SLO-OCT, Heidelberg). Horizontal line scans through the fovea were acquired in all subjects and in a group of 10 age-similar controls. Peripheral SD-OCT scans (extending to 27.5° eccentricity) were also acquired in both eyes of 7 carriers. MP-1 microperimetery (10-2 pattern; Nidek) was performed in one eye of each carrier. For the XLRP carriers, a tapetal reflex was observed with all imaging modalities in 8 of 19 eyes. It had the same retinal location on color fundus, 488-R and NIR-R imaging but a different location on AF. The tapetal reflex was most easily detected in 488-R images. The horizontal foveal SD-OCT scans were qualitatively normal, but measurements showed significant outer retinal layer thinning in all eyes. Additionally, the 14 eyes with peripheral SD-OCTs demonstrated patchy loss of the inner segment ellipsoid band. Microperimetry exhibited patchy visual sensitivity loss in 9 eyes. Full field ERGs were variable, ranging from normal to severely abnormal rod and cone responses. Our findings suggest that an optimal protocol for identifying carriers of XLRP should include 488-R imaging in a multimodal approach. Peripheral SD-OCT imaging and central retinal layer quantification revealed significant structural abnormalities.

Keywords: X-linked retinitis pigmentosa; microperimetry; scanning laser ophthalmoscope; spectral domain optical coherence tomograph; tapetal-like reflex.

Figure 1

Color and SLO fundus images of one healthy individual (top row) and five XLRP carriers (from second row to bottom row: C1,C3, C8, C9, C10) (From left to right) Color fundus (CF), 488 nm reflectance (488-R), near-infrared reflectance (NIR-R) and autofluorescence (AF) images are shown. The tapetal reflex can be appreciated in the perimacular region as radial lines formed by tiny point-like reflexes which may be elongated in patches or clusters. Where visible, the tapetal reflex has a yellow-orange appearance in CF images (see C1, C3, C8 & C10). In 488-R, NIR-R and AF images, where visible (see Table 1), the tapetal reflex appears bright against the grey fundus background.

Figure 2

Pedigree for carriers C1-C4. The pedigree shows five generations of the XLRP family in this study which includes carriers C1-C4.

Figure 3

Segmentation of SD-OCT horizontal scan through the fovea of one XLRP carrier (C8). The layers and bands manually segmented are indicated. INL, inner nuclear layer; OPL, outer plexiform layer; ISe, inner segment ellipsoid band; OS, outer segment; RPE, retinal pigment epithelium; BM, Bruch's membrane; REC+, total receptor; OS+, receptor outer segment plus RPE.

Figure 4

Peripheral SD-OCT scans. Peripheral horizontal line scans through the fovea, extending to an eccentricity of 27.5°, of one normal individual (top) and five XLRP carriers (from second row to bottom row: C10, C1, C3, C8, C9). Enlarged inset image shows peripheral disruption of the ISe (white arrow).

Figure 5

Retinal layer thickness curves. Thickness curves for the total receptor (REC+) and the receptor outer segment plus RPE (OS+) layers are shown. All eyes are transposed to a right eye. The colored lines represent each of the XLRP carriers and the black lines are the mean ± 95% confidence intervals for the controls.

Figure 6

MP-1 10-2 Total Deviation (TD) probability maps superimposed on 488-R fundus images. Four XLRP carriers (top left: C8, top right: C7, bottom left: C10, bottom right: C5) are shown. The TD probability defects show a patchy pattern across the central 10° and visual field sensitivity loss ranges from mild to severe. The fixation pattern is shown in blue around the fixation target (red cross).

Figure 7

Frequency of defect map. The frequency of MP-1 total deviation defects is represented as the percentage of eyes which had a defect of p<5% at each visual field location. All eyes were transposed to a right eye.