Extramacular scanning shows promise in uveitic disorders

By Joanna Lyford, Senior medwireNews Reporter

New optical coherence tomography (OCT) scanning protocols offer enhanced characterization of patients with birdshot chorioretinopathy, UK researchers report.

Writing in JAMA Ophthalmology, Alastair Denniston (University Hospitals Birmingham NHS Trust, Edgbaston) say that extramacular enhanced-depth OCT imaging can detect retinal and choroidal changes even when conventional scans appear unremarkable.

"Use of extramacular scanning may thus allow improved phenotyping of uveitic disorders such as birdshot chorioretinopathy," they write.

Denniston's team collected OCT images from 24 eyes of 12 patients with birdshot chorioretinopathy and from 18 eyes of nine healthy volunteers matched for age and gender.

All images were obtained using enhanced-depth scanning protocols from the macula and four peripheral locations (superior and inferior to the temporal vascular arcades, nasal to the optic disc, and temporal to the macula).

Qualitative and quantitative analysis of the OCT-derived images found that generalized loss of the photoreceptor IS/OS junction differed by scanning location (inferior, 75%; nasal, 54%; superior, 46%; temporal, 41%; and macular, 25%), as did focal loss of the IS/OS junction (inferior, 91%; nasal, 67%; macular, 67%; superior, 59%; temporal, 55%).

The mean retinal thickness at the foveal central subfield was similar in patients with birdshot chorioretinopathy and healthy controls, at 237 µm and 234 µm, respectively.

With regard to choroidal features, thinning or absence of the Sattler layer differed significantly by scanning location (inferior, 58%; nasal, 50%; superior, 34%; macular, 29%; temporal, 17%). The suprachoroidal hyporeflective space also differed by scanning location (temporal, 38%; macular, 30%; superior, 12%; inferior, 4%; nasal, 0%).

Mean choroidal thickness at the foveal center was significantly lower in patients with birdshot chorioretinopathy than in healthy controls, at 276 µm and 337 µm, respectively.

Finally, choroidal thickness at each of the four extramacular locations was significantly reduced in patients with birdshot chorioretinopathy versus controls.

Taken together, this study indicates that OCT images obtained outside the macula often show significant structural changes even when conventional macular imaging appears relatively unremarkable.

Furthermore, in many cases, the scanning protocols used in the present study allowed visualization of the extramacular "transition zone" in which gross structural abnormalities were first seen.

"In our report, the most striking abnormalities seen on extramacular scans involved disruption of the outer retinal substructures," Denniston and co-authors write.

They conclude: "The use of novel scanning protocols, with commercially available OCT devices, allows for enhanced characterization of patients with birdshot chorioretinopathy… [T]he scanning protocols described in our study may be easily applied to the study of other posterior segment diseases and may be of particular use for phenotyping diffuse choroidal inflammatory diseases."

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