Macular atrophy in birdshot retinochoroidopathy: an optical coherence tomography and multifocal electroretinography analysis

Abstract

Purpose: The purpose of this study was to evaluate macular atrophy by frequency-domain optical coherence tomography (OCT) in patients with birdshot retinochoroidopathy and to compare the resulting thickness measures with visual acuity and multifocal electroretinography (mfERG).

Methods: Measures were obtained from 14 eyes of 7 patients with birdshot retinochoroidopathy and 23 normal eyes. Optical coherence tomography-3 measures of macular thinning were related to visual acuity, mfERG response density, and time since diagnosis. Horizontal midline frequency-domain OCT scans identified which layers of the retina were primarily responsible for macular thinning.

Results: All eyes with a history of birdshot retinochoroidopathy for >10 years had abnormal mfERG response densities. Compared with those without anatomic thinning (n = 8), eyes with anatomic thinning (n = 6) had significantly lower visual acuity (P = 0.0006), foveal response density (P = 0.006), and overall mfERG response density (P = 0.009). Segmentation of retinal layers on frequency-domain OCT scans showed that anatomic thinning was as a result of reduction in the receptor 1 layer (REC+), the thickness of the segment extending from the proximal border of the outer plexiform layer to the Bruch membrane-choroid interface.

Conclusion: Macular atrophy, as reflected in OCT evidence of macular thinning and mfERG evidence of macular function, occurs in patients with long-standing birdshot retinochoroidopathy. Measures of retinal layer thicknesses by frequency-domain OCT suggest that the atrophy occurs primarily in the outer retina.

Figure 1

Segmentation of fdOCT horizontal midline scans in a normal subject (top) and patient #1 with birdshot retinochoroidopathy (bottom). A. Vitreous/RNFL B. RFNL/GCL C. IPL/INL D. INL/OPL E. BM/choroid. Total Retinal Thickness (TR) is the distance between A and E. Retinal nerve fiber layer thickness (RNFL) is the distance between A and B. Inner nuclear layer thickness (INL) is the distance between C and D. REC+ is the distance between D and E.

Figure 2

Horizontal midline fdOCT scans and mfERG results from the right eyes of all seven patients. Left column: fdOCT scans from each patient; Middle column: mfERG responses shown in field view with calibration markers indicating 200 nV/deg² and 50 msec; Right column: mfERG density plots refined through interpolation with twice the resolution as the 103 stimulus hexagons.

Figure 3

Thickness measurements from fdOCTs. The solid curve is the mean of 23 normal subjects; the shaded area indicates ± 2 standard deviations. Closed symbols (solid lines) and open symbols (dashed lines) show OD and OS, respectively, of the same patient. Most patients show a reduction in total thickness throughout the macula. This is primarily due to a reduction in REC+. Inner nuclear layer thickness is normal except in two eyes with macular edema involving the inner retina.