Objective assessment of a relative afferent pupillary defect by B-mode ultrasound.

Purpose: To evaluate B-mode ultrasound as a novel method for objective and quantitative assessment of a relative afferent pupillary defect (RAPD) in a prospective case-control study.
Methods: Seventeen patients with unilateral optic neuropathy and a clinically detectable RAPD and 17 age and sex matched healthy controls were examined with B-mode ultrasound using an Esaote-Mylab25 system according to current guidelines for orbital insonation. The swinging flashlight test was performed during ultrasound assessment with a standardized light stimulus using a penlight.
Results: B-mode ultrasound RAPD examination was doable in approximately 5 minutes only and was well tolerated by all participants. Compared to the unaffected contralateral eyes, eyes with RAPD showed lower absolute constriction amplitude of the pupillary diameter (mean [SD] 0.8 [0.4] vs. 2.1 [0.4] mm; p = 0.009) and a longer pupillary constriction time after ipsilateral light stimulus (mean [SD] 1240 [180] vs. 710 [200] ms; p = 0.008). In eyes affected by RAPD, visual acuity correlated with the absolute constriction amplitude (r = 0.75, p = 0.001).
Conclusions: B-mode ultrasound enables fast, easy and objective quantification of a RAPD and can thus be applied in clinical practice to document a RAPD.
Competing Interests: F Schmidt has received speaker honoraria from Genzyme, outside the submitted work. K Ruprecht has received research support from Novartis and Bundesministerium für Bildung und Forschung (Competence Network Multiple Sclerosis) as well as speaking fees or travel grants from Guthy Jackson Charitable Foundation and Biogen, outside the submitted work. F Connolly has nothing to disclose. M Maas receives funding from National Institutes of Health grants K23NS092975 and L30NS080176, and has served as a technical consultant for Hyperfine Research, outside the submitted work. F Paul reports grants from BMBF, grants from BMBF, grants from DFG, grants from GJCF, grants from Novartis, personal fees from Bayer, Teva, Genzyme, Merck, MedImmune and Novartis, outside the submitted work. L Harms has received speaker honoraria from Biogen, Teva, Bayer and Novartis. He serves on the advisory board for Roche, Novartis, Genzyme and has received travel support from Biogen, Roche, Bayer and Serono, outside the submitted work. S Schreiber has nothing to disclose. This does not alter our adherence to PLOS ONE policies on sharing data and materials.