http://orcid.org/0000-0003-1307-1513
Figures
Abstract
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).
Citation: Schmidt FA, Connolly F, Maas MB, Grittner U, Harms L, Brandt A, et al. (2018) Objective assessment of a relative afferent pupillary defect by B-mode ultrasound. PLoS ONE 13(8): e0202774. https://doi.org/10.1371/journal.pone.0202774
Editor: Raja Narayanan, LV Prasad Eye Institute, INDIA
Received: May 16, 2018; Accepted: August 8, 2018; Published: August 27, 2018
Copyright: © 2018 Schmidt et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper and its Supporting Information files.
Funding: The authors received no specific funding for this work.
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.
Introduction
A relative afferent pupillary defect (RAPD) is an impairment of the pupillary light reflex (PLR) upon an ipsilateral light stimulus, typically due to ipsilateral optic nerve dysfunction [1]. At the bedside, presence of a RAPD is commonly tested by the swinging flashlight test, during which a penlight is swung from the unaffected eye to the affected eye while the PLR is observed. In pathological conditions, the pupil of the affected eye constricts normally following a contralateral (indirect) light stimulus (Lstim), but shows a reduced or absent constriction, or even a paradoxical dilatation, following an ipsilateral (direct) Lstim [2]. The most common underlying pathology of RAPD is optic neuritis (ON), which can occur in a variety of neuroimmunological disorders such as multiple sclerosis, neuromyelitis optica spectrum disorder, myelin oligodendrocyte glycoprotein antibody associated encephalomyelitis or sarcoidosis [3–7]. While, in our center, B-mode ultrasound is an established method for quantitatively measuring pupil diameter [8], the role of B-mode ultrasound in the assessment of a RAPD has not been systematically studied so far. Here, we evaluate B-mode ultrasound for objective and quantitative assessment of a RAPD.
Material and methods
Study participants
In this prospective case-control study, study participants were recruited from the Department of Neurology and from the NeuroCure Clinical Research Center, Charité–Universitätsmedizin Berlin. Inclusion criteria were age 18 to 65 years, and a clinically detectable RAPD due to unilateral ON. RAPD was diagnosed clinically by bedside examination with the swinging flashlight test by a trained physician [2]. We excluded patients with a history of any ocular disease other than ON (e.g. glaucoma, cataract, macular degeneration or diabetic retinopathy), those who had undergone any type of ocular surgery in the past including laser surgery, and those taking any topical or systemic medications known to potentially affect pupillary function. Data from healthy controls were taken from a previous study on B mode ultrasound assessment of the PLR in healthy individuals [8]. Healthy controls had no prior or current ophthalmologic disease, no medications known to potentially affect pupillary function, and were selected from our database to match patients for age (± 1 years) and sex.
Visual acuity testing
Habitual corrected visual acuity was determined under standardized light conditions using a Snellen Chart with a distance of 2.8 meter [9].
B-mode ultrasound technique
All participants were studied in supine position under standardized dimmed light conditions (room lighting 30 Lux). To adapt to the light level, study participants spent at least 10 minutes in the ultrasound examination room before testing. All insonations were performed by the same investigator (SJS) with the subject’s eyes closed using an Esaote Mylab 25 system (Esaote, Indianapolis, USA) equipped with a linear 10 MHz probe. Power settings were reduced to minimum, according to the ALARA (as low as reasonably achievable) insonation approach and current guidelines for orbital insonation [10]. B-mode settings were adjusted for near-field eye examination. Each patient was examined lying flatly on the examination bed facing towards the ceiling. Each pupil was visualized with the probe gently positioned at an angle of 20–30 degree from the examination bed on the lower eyelid of the closed eye, leveraging Bell’s phenomenon [8]. For assessment of the PLR, patients had their eyes closed, a penlight was activated approximately 2 cm in front of each closed eye and the light reaction of each pupil was digitally documented. In every examination the same standard penlight was used with a luminous emittance of 70,000 Lux and a stimulus time of 2 seconds to ensure constant wavelength, intensity and duration of the light stimulus. Each assessment was performed in exactly the same order, starting by measuring the pupillary diameter (PD) of the left eye at rest as well as during ipsilateral and contralateral Lstim, followed by the same examinations of the right eye.
Data analyses
RAPDs were documented by recording video sequences of ultrasound examinations of the PLR during performance of the swinging flashlight test [2]. PDs were manually assessed in a frozen still image of the pupil, which was then digitally stored. Using the measuring tool of the native application ultrasound system software, the largest diameter at rest and the smallest diameter after Lstim were measured. Pupillary constriction time (PCT, measured in milliseconds) was defined as the time interval between the maximum and the minimum PD during Lstim. PCT was manually determined using the AVSVideoConverter9.2 freeware (Online Media Technologies Ltd. London, UK) in recorded 5 second video sequences of a second ipsi- and contralateral Lstim, approximately 2 min after the PD analysis.
Statistical analyses
Statistical analyses were performed using SPSS 23.0 (IBM SPSS Statistics, New York, USA). Graphs were created with GraphPadPrism 7.0 (GraphPad Software Inc, La Jola, USA). PD and PCT are reported as mean ± standard deviation. PLR assessment measures in patients with RAPD were compared with same-sided eyes of healthy controls using Student´s t-test for independent samples for continuous variables or Mann-Whitney-U-test, depending on the distribution. Differences between affected and non-affected eyes in patients were tested using Wilcoxon signed-rank-test. Associations between visual acuity and PLR assessment measures were analyzed using Pearson’s correlation coefficient. We also calculated the ratio of the consensual/direct absolute constriction amplitude for each eye to quantitatively express the severity of the RAPD (“constriction ratio”). Correlation of the constriction ratio with visual acuity was analyzed using Spearman’s rank correlation coefficient. P-values were corrected for multiple testing according to the Bonferroni method [11]. Thus, each p-value was multiplied by the number of statistical tests performed (n = 30). A two-sided significance level of α = 0.05 was considered significant.
The study was approved by the institutional review board of Charité—Universitätsmedizin Berlin (EA1/190/15) and all participants provided written informed consent.
Results
Study participants
We studied 17 patients with unilateral ON and a clinically detectable RAPD. Of these, 5 had ON as a clinically isolated syndrome (CIS), 4 had relapsing remitting multiple sclerosis according to the McDonald 2010 criteria [12], 6 had neuromyelitis optica spectrum disorder according to the Wingerchuk 2015 criteria [13], and 2 had ON of unknown etiology. The demographics and clinical characteristics of the patients and controls are summarized in Table 1.
In patients with a RAPD, the visual acuity of affected eyes was significantly lower compared to the same-sided eyes of controls (mean [SD] 0.4 [0.2] vs. 1.0 [0.1]; p<0.001) and compared to the unaffected fellow eyes (0.4 [0.2] vs. 0.9 [0.1]; p = 0.008) (Table 2).
B-mode ultrasound for assessment of RAPD
The average ultrasound examination was doable in approximately five minutes and was well tolerated by all participants. In all 17 patients with a clinically detectable RAPD, RAPD was also detectable with B-mode ultrasound. Results of visual acuity testing, pupil diameter and PCT assessment are summarized in Table 2. For illustration of RAPD assessment with B-mode ultrasound, a video sequence of a 42-year-old male with left ON due to multiple sclerosis is provided as supplementary video material (S1 Video).
Absolute constriction amplitudes
During ipsilateral Lstim of the affected eye the direct constriction amplitude was smaller in the affected eyes compared to the same-sided eyes of controls (mean [SD] 0.8 [0.4] vs. 2.0 [0.5] mm; p<0.001) and compared to the unaffected fellow eyes (0.8 [0.4] vs. 2.1 [0.4] mm; p = 0.009) (Table 2). Consequently, during ipsilateral Lstim of the affected eye the consensual constriction amplitude in the unaffected eye was smaller compared to same-sided eyes of controls (mean [SD] 1.1 [0.5] vs. 1.9 [0.4] mm; p<0.001) and compared to the consensual constriction amplitude of affected eyes (1.1 [0.5] vs. 1.9 [0.5]; p = 0.019) (Table 2).
Constriction ratio
As a quantitative measure of RAPD severity we calculated the constriction ratio, defined as the quotient of the consensual to direct constriction amplitudes. The constriction ratio was higher in the affected eyes than in the same-sided eyes of controls (mean [SD] 2.8 [1.7] vs 1.0 [0.1]; p<0.001) and lower in the unaffected fellow eyes compared to controls (0.6 [0.2] vs. 1.0 [0.1]; p<0.001) (Table 2). To establish a cut-off value that distinguishes between pathological and normal ratios, we calculated the mean + 3 standard deviations of the constriction ratio of the control eyes (i.e. 1.3) and defined values above this value as pathological. As shown in Fig 1, a threshold value of >1.3 discriminated eyes with a clinically-defined RAPD and healthy control eyes without any overlap, suggesting that this measure could be used in clinical practice for a diagnosis of a RAPD by B-mode ultrasound.
X-axis: affected eyes and HC eyes. Y-axis: Constriction ratio of consensual to direct constriction amplitudes; the whiskers indicate minimum and maximum values. HC = healthy controls, ON = optic neuritis.
Pupillary constriction times
During ipsilateral Lstim, PCT was longer in the affected eyes compared to the same-sided eyes of controls (mean [SD] 1240 [180] vs. 830 [130] ms; p<0.001) and compared to the unaffected fellow eyes (1240 [180] vs. 710 [200] ms; p = 0.008). During contralateral Lstim, PCT was longer in the unaffected eyes compared to the same-sided control eyes (mean [SD] 1080 [250] vs. 890 [100] ms; p<0.001) and compared to affected eyes (1080 [250] vs. 750 [190] ms; p = 0.007).
Correlation of visual acuity with pupillary constriction
The visual acuity of the affected eyes was correlated with the direct constriction amplitude of the affected eye (r = 0.75, p = 0.001, Fig 2) and with the consensual constriction amplitude of the contralateral eye (r = 0.74, p = 0.001). The visual acuity of the affected eye was inversely correlated with the constriction ratio of the affected eye (r = -0.66, p = 0.004).
X-axis: ACAdir = difference between pupillary diameter at rest and during ipsilateral light stimulus, ON = optic neuritis. Y-axis: VA = visual acuity.
Discussion
We here report on the application of B-mode ultrasound as a novel method for the detection and quantification of a RAPD. B-mode ultrasound assessment of RAPD was fast, simple and well–tolerated, and enabled unambiguous detection of a RAPD in patients with a clinically detectable RAPD due to unilateral ON. As expected, ultrasound measurements showed reduced constriction amplitudes in both eyes following light stimulation of the affected eye compared to contralateral light stimulation. Furthermore, the severity of the RAPD as assessed by B-mode ultrasound correlated with the severity of visual acuity impairment.
Compared to standard clinical RAPD examination by the swinging flashlight test [1, 2], advantages of RAPD testing by B-mode ultrasound include objective quantification of the severity of a RAPD and digital documentation of results of RAPD examinations. Parameters and ultrasound images can thus be stored and analyzed longitudinally in follow-up measurements. Furthermore, the dynamic component of the PLR, the PCT, can be measured and documented as well.
The results for constriction amplitude differences obtained by B-mode ultrasound were overall similar to those of studies examining patients with RAPD and controls with infrared video pupillometry (IVP) [14–17]. While IVP allows for a marginally more detailed analysis of the PLR [18], IVP devices are sophisticated tools with limited availability due to high acquisitions costs. In contrast, ultrasound is a widely available standard diagnostic tool in most hospitals and medical practices. Furthermore, unlike IVP, PLR assessment by ultrasound can be performed with the patient´s eyes closed, so examinations are still feasible in cases in which eyelid retraction is impeded.
To distinguish in clinical routine between healthy and pathological reactions, we propose a threshold value of >1.3 of the consensual to direct constriction amplitude ratio as suggestive of RAPD. To determine this threshold, we applied the “mean + 3 standard deviation of negative controls” formula, a widely used formula to determine cut-offs for biological tests [19]. The constriction ratio can be measured with B-mode ultrasound within approximately 2 min and could help to identify a RAPD when it is not clearly detectable with the swinging flashlight test [2]. Furthermore, constriction ratios could be longitudinally evaluated in follow-up examinations to document RAPD severity and to monitor treatment effects in patients with inflammatory optic neuropathies. Determination of an RAPD by B-mode ultrasound can measure functional integrity of the anterior visual pathway, whereas optical coherence tomography measures structural damage of the retina, and visual evoked potentials measure functional integrity of the entire visual pathway. B-mode ultrasound of the eye could thus complement visual evoked potentials [6,20] and optical coherence tomography [21–24], in the assessment of the visual pathway and could thus help to investigate afferent anterior visual pathway damage in patients with inflammatory conditions, such as CIS, MS, NMOSD or MOG antibody associated encephalomyelitis [25–29].
Of note, our findings may also have implications for treatment trials with visual endpoints. For instance, one of the recent NMOSD trials investigating the clinical efficiency of a CD19 monoclonal antibody has implemented RAPD as an attack criterion [30]. Similar trials could potentially benefit from a reliable and reproducible RAPD evaluation method such as the B-mode ultrasound proposed here. Thus, longitudinal studies with follow-up measurements of RAPD by ultrasound and their correlation to visual acuity and treatment response would be of interest. Furthermore, it will be interesting to evaluate in patients with ON and no clinical sign of RAPD whether subclinical RAPD can be detected by ultrasound.
Altogether, B-mode ultrasound enables fast, easy and objective quantification of a RAPD and can thus be applied in clinical practice to document a RAPD.
References
- 1. Bremner FD. Pupil assessment in optic nerve disorders. Eye (Lond) 2004; 18(11):1175–81.
- 2. Thompson H.S., Corbett J.J., Cox T.A. How to measure the relative afferent pupillary defect. Surv Ophthalmol 1981; 26:39–42. pmid:7280994
- 3. Petzold A, Wattjes MP, Costello F, Flores-Rivera J, Fraser CL, Fujihara K et al. The investigation of acute optic neuritis: a review and proposed protocol. Nat Rev Neurol 2014; 10(8):447–58. pmid:25002105
- 4. Galetta SL, Villoslada P, Levin N, Shindler K, Ishikawa H, Parr E et al. Acute optic neuritis: Unmet clinical needs and model for new therapies. Neurol Neuroimmunol Neuroinflamm 2015; 2(4):e135. pmid:26236761
- 5. Bennett JL, de Seze J, Lana-Peixoto M, Palace J, Waldman A, Schippling S et al. Neuromyelitis optica and multiple sclerosis: Seeing differences through optical coherence tomography. Mult Scler 2015; 21(6):678–88 pmid:25662342
- 6. Waldman AT, Liu GT, Lavery AM, Liu G, Gaetz W, Aleman TS et al. Optical coherence tomography and visual evoked potentials in pediatric MS. Neurol Neuroimmunol Neuroinflamm; 4(4):e365.
- 7. Kidd DP, Burton BJ, Graham EM, Plant G. Optical neuropathy associated with systemic sarcoidosis. Neurol Neuroimmunol Neuroinflamm; 3(5):e270. pmid:27536707
- 8. Schmidt FA, Ruprecht K, Connolly F, Maas MB, Paul F, Hoffmann J et al. B-mode ultrasound assessment of pupillary function: Feasibility, reliability and normal values. PLos One 2017; 12(12):e0189016. pmid:29211788
- 9. McGraw P, Winn B, Whitaker D. Reliability of the Snellen Chart. BMJ 1995; 310(6993):1481–2. pmid:7787581
- 10. Trier HG. Use of ultrasound in ophthalmology. Ultraschall Med 1982 3(4):164–71. pmid:9417619
- 11. Ludbrook J. Multiple comparison procedures updated. Clin Exp Pharmacol Physiol 1998; 25(12):1032–7. pmid:9888002
- 12. Polman CH, Reingold SC, Banwell B, Clanet M, Cohen JA, Filippi M, et al. Diagnostic criteria for multiple sclerosis: 2010 Revisions to the McDonald criteria. Ann Neurol. 2011; 69(2):292–302. pmid:21387374
- 13. Wingerchuk DM, Banwell B, Bennett JL, Cabre P, Carrol W, Chitnis T et al. International consensus diagnostic criteria for neuromyelitis optica spectrum disorders. Neurology 2015; 85(2):177–89. pmid:26092914
- 14. Volpe NJ, Plotkin ES, Maguire MG, Hariprasad R, Galetta SL. Portable pupillography of the swinging flashlight test to detect afferent pupillary defects. Ophthalmology 2000; 107(10):1913–21. pmid:11013198
- 15. Cayless A, Bende T. First results of automated RAPD-SWIFT method in dynamic pupillometry. Z Med Phys 2016; 26(2):143–9. pmid:26542387
- 16. Kalaboukhova L, Fridhammar V, Lindblom B. Relative afferent pupillary defect in glaucoma: a pupillometric study. Acta Opthalmol Scand 2007, 85(5):519–25.
- 17. Lankaranian D, Altangerel U, Spaeth GL, Leavitt JA, Steinmann WC. The usefulness of a new method of testing for a relative afferent pupillary defect in patients with ocular hypertension and glaucoma. Trans Am Ophthalmol Soc 2005, 103:200–7. pmid:17057803
- 18. Löwenfeld IE, Rosskothen HD. Infrared pupil camera. A new method for mass screening and clinical use. Am J Ophthalmol 1974; 78(2):304–13. pmid:4847467
- 19. Ridge SE, Vizard AL. Determination of the optimal cutoff value for a serological assay: an example using the Johne´s Absorbed EIA. J Clin Mivrobiol 1993; 31(5):1256–1261.
- 20. Di Maggio G, Santangelo R, Guerrieri S, Bianco M, Ferrari L, Medaglini S et al. Optical coherence tomography and visual evoked potentials: which is more sensitive in multiple sclerosis? Mult Scler 2014; 20(10):1342–7. pmid:24591532
- 21. Martinez-Lapisczina EH, Arnow S, Wilson JA, Saidha S, Preiningerova JA, Oberwahrenbrock T et al. Retinal thickness measured with optical coherence tomography and risk of disability worsening in multiple sclerosis: a cohort study. Lancet Neurol 2016; 15(6):574–84. pmid:27011339
- 22. Schippling S, Balk LJ, Costello F, Albrecht P, Balcer L, Calabresi PA et al. Quality control for retinal OCT in multiple sclerosis: validation of the OSCAR-IB criteria. Mult Scler. 2015; 21(2):163–70. pmid:24948688
- 23. Oberwahrenbrock T, Schippling S, Ringelstein M, Kaufhold F, Zimmermann H, Keser N et al. Retinal damage in multiple sclerosis disease subtypes measured by high-resolution optical coherence tomography. Mult Scler Int. 2012;2012:530305. pmid:22888431
- 24. Schmidt F, Zimmermann H, Mikolajczak J, Oertel FC, Pache F, Weinhold M et al. Severe structural and functional visual system damage leads to profound loss of vision-related quality of life in patients with Neuromyelitis optica spectrum disorders. Mult Scler Relat Disord. 2017; 11:45–50. pmid:28104256
- 25. Pache F, Zimmermann H, Mikolajczak J, Schumacher S, Lacheta A, Oertel FC et al. MOG-IgG in NMO and related disorders: a multicenter study of 50 patients. Part 4: Afferent visual system damage after optic neuritis in MOG-IgG-seropostive versus AQP4-IgG-seropositive patients. J Neuroinflammation 2016; 13(1):282. pmid:27802824
- 26. Sepulveda M, Armangué T, Sola-Valls N, Arrambide G, Meca-Lallana JE, Oreja-Guevara C et al. Neuromyelitis optica spectrum disorders: Comparison according to the phenotype and serostatus. Neurol Neuroimmunol Neuroinflamm 2016; 3(3):e225. pmid:27144216
- 27. Oertel FC, Kuchling J, Zimmermann H, Chien C, Schmidt F, Knier B et al. Microstructural visual system changes in AQP4-antibody-seropositive NMOSD. Neurol Neuroimmunol Neuroinflamm 2017; 4(3):e334. pmid:28255575
- 28. Bennett JL, O´Connor KC, Bar-Or A, Zamvil SS, Hemmer B, Tedder TF et al. B lymphocytes in Neuromyelitis optica. Neurol Neuroimmunol Neuroinflamm 2015; 2(3):e104. pmid:25977932
- 29. Kuchling J, Brandt AU, Paul F, Scheel M. Diffusion tensor imaging for multilevel assessment of the visual pathway: possibilities for personalized outcome prediction in autoimmune disorders of the central nervous system. EPMA 2017; 8(3):279–294.
- 30. Cree BA, Bennett JL, Sheehan M, Cohen J, Hartung HP, Aktas O et al. Placebo-controlled study in neuromyelitis optica—Ethical and design considerations. Mult Scler 2016; 22(7):8622–722.