Color Pupillography in Dorsal Midbrain Syndrome

The purpose of this study was to evaluate the pupil response to chromatic stimuli in patients with lesions in the dorsal midbrain and possibly gain new insights into the afferent pupillary pathways. Color pupillography was performed in 5 patients with dorsal midbrain syndrome (DMS), and their results were compared with those of 20 healthy control subjects. We used full-field red stimuli (605 nm) that primarily address the rod/cone system and blue stimuli (420 nm) that preferentially activate intrinsically photosensitive retinal ganglion cells (ipRGCs) directly, with a duration of 4 seconds and a stimulus intensity of 28 lx corneal illumination under mesopic conditions. One eye was stimulated, and the consensual pupil response was recorded and analyzed. The pupillary light reflex in patients with DMS was reduced, differed in shape, and showed a prolonged latency time compared to normal subjects. The blue response was less affected than the red response: the mean maximal relative amplitude (M) was 15.8% (SD = 7.8) in patients with DMS compared with 43.0% (SD = 5.5) in normal subjects for red stimulation, and M = 40.8%, SD = 8.4 (DMS) with M = 58.3%, SD = 4.8 (normals) for blue stimulation. The reduction was 63% for red stimulation but only 30% for blue stimulation in patients with DMS. Moreover, there was a preserved postillumination pupil response to blue stimulation in DMS patients. In DMS, the melanopsin-mediated ipRGC pathway appeared relatively preserved.

Original Contribution Color Pupillography in Dorsal Midbrain Syndrome Carina B. Kelbsch, DrMed, Fumiatsu Maeda, PhD, Torsten Strasser, Dr sc hum, MSc, Tobias M. Peters, DrMed, Barbara J. C. Wilhelm, DrMed, Helmut M. Wilhelm, DrMed Objective: The purpose of this study was to evaluate the pupil response to chromatic stimuli in patients with lesions in the dorsal midbrain and possibly gain new insights into the afferent pupillary pathways. Methods: Color pupillography was performed in 5 patients with dorsal midbrain syndrome (DMS), and their results were compared with those of 20 healthy control subjects. We used full-field red stimuli (605 nm) that primarily address the rod/cone system and blue stimuli (420 nm) that preferentially activate intrinsically photosensitive retinal ganglion cells (ipRGCs) directly, with a duration of 4 seconds and a stimulus intensity of 28 lx corneal illumination under mesopic conditions. One eye was stimulated, and the consensual pupil response was recorded and analyzed. Results: The pupillary light reflex in patients with DMS was reduced, differed in shape, and showed a prolonged latency time compared to normal subjects. The blue response was less affected than the red response: the mean maximal relative amplitude (M) was 15.8% (SD = 7.8) in patients with DMS compared with 43.0% (SD = 5.5) in normal subjects for red stimulation, and M = 40.8%, SD = 8.4 (DMS) with M = 58.3%, SD = 4.8 (normals) for blue stimulation. The reduction was 63% for red stimulation but only 30% for blue stimulation in patients with DMS. Moreover, there was a preserved postillumination pupil response to blue stimulation in DMS patients. Conclusions: In DMS, the melanopsin-mediated ipRGC pathway appeared relatively preserved. Journal of Neuro-Ophthalmology 2017;37:247-252 doi: 10.1097/WNO.0000000000000527 © 2017 by North American Neuro-Ophthalmology Society Pupil Research Group at the Centre for Ophthalmology (CK, FM, TS, TP, BW, HW), University of Tübingen, Tübingen, Germany; Department of Orthoptics and Visual Sciences (FM), Faculty of Medical Technology, Niigata University of Health and Welfare, Niigata, Japan; and Institute for Ophthalmic Research (TS), University of Tübingen, Tübingen, Germany. Supported by the Egon Schumacher-Stiftung, Germany, a private foundation without commercial interest. The authors report no conflicts of interest. Address correspondence to Carina Kelbsch, DrMed, Centre for Ophthalmology, University of Tübingen, Elfriede-Aulhorn-Straße 7, 72076 Tübingen, Germany; E-mail: [e-mail] Kelbsch et al: J Neuro-Ophthalmol 2017; 37: 247-252 T he pupillary light reaction has been considered to be a simple subcortical reflex arc through a direct retinopretectal projection involving photoreceptors, retinal ganglion cells, the pretectum, the Edinger-Westphal nucleus, and the ciliary ganglion (1). However, research over several decades has shown that there are cortical inputs affecting the pupillary light reflex, at least under certain stimulation conditions (2- 11). In addition to the classic photoreceptor activation of rods and cones, the melanopsin-driven response of the intrinsically photosensitive retinal ganglion cells (ipRGCs) also contributes to the pupillary light reflex (12-20). This led to the hypothesis of the existence of 2 separate pupillary afferent systems: one subcortical pathway, that is melanopsin driven by the ipRGCs, the other running synaptically through the rod/cone system with input of the visual cortex. This hypothesis is based on our previous study on patients with hemianopia due to postgeniculate lesions that revealed well-preserved pupil responses to blue stimulation but significantly reduced pupil responses to red stimulation. It is known that the photopigment melanopsin, responsible for the intrinsic photosensitivity of ipRGCs (12,13), shows a peak spectral sensitivity at around 480 nm (14,17,20) and determines the characteristic sustained pupil constriction that can be observed after stimulation with bright blue light, the postillumination pupil response (PIPR) (14,18). Comparing pupil responses to stimulation with either bright blue (rod/cone and melanopsin activation) or red light (rod/cone but no relevant melanopsin activation) allows for predictions about the intrinsic contribution of ipRGCs of the inner retina vs the extrinsic rod/cone-driven response of the outer retina. Chromatic pupillography has been proven to be useful in several retinal disorders, e.g. retinitis pigmentosa, where reduced rod/cone-dependent but increased melanopsin-dependent pupillary responses can be observed (21-23), whereas in glaucoma, a reduced melanopsin-dependent PIPR has been demonstrated (24,25). Studies in patients with localized lesions of the pupillary pathways are a possibility to gain more information. Patients with lesions in the dorsal midbrain typically show bilaterally absent or, at least, markedly reduced pupillary light reaction 247 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Statistical analysis was carried out with Microsoft Visual Basic for Applications 7.0 in Excel 2010 (Microsoft, 248 Surgery Surgery Radiotherapy Radiotherapy Radiotherapy Absent; impaired Impaired; normal Impaired; impaired Impaired; impaired Impaired; impaired + + + + + L: 20/25 L: 20/16 L: 20/20 L:20/20 L:20/20 L L R L R R: R: R: R: R: Visual Acuity Eye for Analysis Diagnosis Pineal tumor Pineal epidermoid Pineal germinoma Brainstem germinoma Pineal blastoma 39/F 39/M 58/M 27/M 24/F L-N, light-near. Statistical Analysis Age, yr/Sex Color pupillography was performed under mesopic conditions (1-2 cd/m2) using a custom-made pupillography setup consisting of 2 devices: the Compact Integrated Pupillograph CiP (AMTech, Dossenheim, Germany) for recording of the pupil responses and a mini Ganzfeld color LED stimulator (CH Electronics, Bromley, United Kingdom) for stimulation. One eye was stimulated, and the consensual pupil reaction was recorded with a spatial resolution of 0.05 mm and a temporal resolution of 250 Hz for 16 seconds, including a period of 5 seconds of prestimulus time for baseline determination. Stimulus intensity was 28 lux of corneal illumination, stimulus duration was 4 seconds, and the stimulus wavelengths were 605 ± 20 nm (red stimulation) and 420 ± 20 nm (blue stimulation). More details are provided elsewhere (24). For each wavelength condition, the measurements were repeated until 4 good quality pupillograms with few artefacts could be recorded. They were averaged and analyzed offline. Patient Color Pupillography TABLE 1. Clinical characteristics of patients with dorsal midbrain syndrome We examined 5 patients between 24 and 58 years of age with the diagnosis of DMS confirmed clinically and by neuroimaging studies. Twenty healthy subjects (mean age 41.4 ± 13 years) served as a control group. All subjects underwent a complete ophthalmological examination including visual acuity, pupil testing, slit lamp examination, and ophthalmoscopy. One subject (Patient 5) showed mild temporal optic disc pallor bilaterally due to previous papilledema, but the remaining patients showed no evidence of afferent visual pathway abnormalities. Patient 2 was included in a previous publication (29). Informed consent was obtained from all participants. The study followed the tenets of the Declaration of Helsinki and was approved by the local ethics committee of Tübingen. Pupillary L-N Dissociation Participants 1 2 3 4 5 METHODS 20/20, 20/16, 20/16, 20/20, 20/16, Upgaze; Saccades/Pursuits Last Treatment Time Since Last Treatment with well-preserved near reaction (pupillary light-near dissociation) in addition to other findings including upward gaze palsy with a preserved vestibular ocular reflex, convergence- retraction nystagmus, lid retraction, strabismus, and papilledema (26,27). Typically, the pupillary light reaction is not completely absent, as stimulation with high intensities elicits a slow, tonic, residual pupil response with prolonged latency periods and reduced extent of constriction (28). The purpose of our study was to evaluate how patients with dorsal midbrain syndrome (DMS) respond to light of different wavelengths designed to preferentially stimulate either ipRGCs directly (bright blue light) or the rod/cone system (red light). 3 mo 24 yr 15 yr 8 yr 18 yr Original Contribution Kelbsch et al: J Neuro-Ophthalmol 2017; 37: 247-252 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution Redmond, WA). A customized filter served for the extraction of blink artefacts. For each participant, either the right or the left eye was randomized for the statistical analysis. Pupil parameters for the data analysis were as follows: baseline pupil diameter (mm), latency (ms), relative amplitude at maximal constriction, at stimulus offset, at 3 seconds after stimulus offset, at 7 seconds after stimulus offset (%), and time to maximal constriction (seconds). Baseline pupil diameter was defined as the median pupil diameter of a 5second prestimulus period and latency as the time between stimulus onset and the beginning of a detectable pupil constriction. The absolute pupil diameter at any time was converted into the relative amplitude (relative amplitude = [1 2 absolute pupil diameter/baseline] · 100). The time to maximal constriction was defined as the time between stimulus onset and the maximal constriction amplitude. The ratio between the relative amplitude at maximal constriction for blue and red stimulation was calculated. For all variables, statistical analysis of the mean values was done by unpaired t tests and revealed partially significant differences between patients with DMS and controls, but due to the small number of study patients, we performed descriptive statistical analysis instead of reporting P values. In addition, for statistical analysis of the main variable, the relative amplitude at maximal constriction, and the PIPR (relative amplitudes at 3/7 seconds after stimulus offset), we compared the patients' individual data with the normal distribution provided by the control subjects (mean ± 1.96 SD). Values outside this range were considered significant. RESULTS Five patients were included in our study (Table 1). Figure 1 shows the average pupil responses to red and blue stimulation from the normal control group (n = 20) and from the patients with DMS. The shape of the pupillographic curves from the patients differed considerably from that of the normal cohort. For both blue and red stimuli, we found reduced maximal relative amplitudes, a prolonged latency time, and a delayed time to maximum constriction in the patient group compared with the normal controls (Fig. 1; Table 2). FIG. 1. Relative amplitude (%) vs time (seconds) for blue and red stimulation (stimulus duration of 4 seconds is marked gray) in a reference group of 20 normal control subjects (with 95% confidence interval) and in 5 patients with DMS (mean out of 4 pupillograms), respectively. DMS, dorsal midbrain syndrome; s, seconds. Kelbsch et al: J Neuro-Ophthalmol 2017; 37: 247-252 249 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution TABLE 2. Comparison of mean results for several pupillary parameters in patients with DMS and healthy controls Number Age, y Blue response Relative amplitude At maximum constriction, % At stimulus offset, % At 3 s after stimulus offset, % At 7 s after stimulus offset, % Baseline, mm Latency, ms Time to maximum constriction, s Red response Relative amplitude At maximum constriction, % At stimulus offset, % At 3 s after stimulus offset, % At 7 s after stimulus offset, % Baseline, mm Latency, ms Time to maximum constriction, s DMS Controls 5 37.4 ± 13.4 20 41.4 ± 13.0 40.8 ± 8.4 40.1 ± 9.1 25.0 ± 9.1 19.8 ± 8.9 5.91 ± 0.78 472.8 ± 143.6 4.26 ± 0.18 58.3 ± 4.8 57.5 ± 4.6 26.2 ± 5.9 17.1 ± 6.6 6.15 ± 0.98 261.0 ± 19.7 3.44 ± 0.71 15.8 ± 7.8 15.1 ± 8.1 3.4 ± 3.5 1.8 ± 1.9 6.12 ± 0.76 437.6 ± 188.5 3.76 ± 0.58 43.0 ± 5.5 38.4 ± 6.1 12.7 ± 5.3 5.0 ± 4.0 6.22 ± 0.99 270.0 ± 22.0 2.08 ± 0.92 DMS, dorsal midbrain syndrome; mm, millimeters; ms, milliseconds; s, seconds; y, years. DMS patients. This effect is also shown by calculating the ratio between the maximal relative amplitudes for blue and red stimulation. All 5 DMS patients revealed significantly higher ratios blue/red outside the 1.96 SD of the normal cohort (DMS: M = 3.48, SD = 2.16; normals M = 1.37, SD = 0.14) (Table 3). There was no significant difference in the melanopsinmediated PIPR after blue stimulation (relative amplitude at 3 or 7 seconds after stimulus offset) between DMS patients and normals (Tables 2 and 3), and no pupillary escape behavior during exposure to red light could be observed (no significant redilation until stimulus offset; Table 2). For red stimulation, in the patient group, the maximal relative pupil constriction ranged from 3.64% to 23.29% (M [mean] = 15.8%, SD = 7.8; normals M = 43.0%, SD = 5.5, range: 31.3%-54.1%). Each individual patient's value was outside the 1.96 SD of the normal cohort (Table 3). The mean reduction of the maximal relative amplitude compared with normals was 63%. For blue stimulation, the maximal relative amplitudes ranged from 28.06% to 49.12% (M = 40.8%, SD = 8.4) with a mean reduction of 30% compared with normals (M = 58.3%, SD = 4.8, range: 49.0%-65.8%). The blue response was much less affected than the red response in TABLE 3. Relative amplitudes for patients with DMS at maximal constriction (mean out of 4 pupillograms) for blue and red stimulation and their ratio blue/red as well as the melanopsin-mediated postillumination pupil response for blue stimulation (relative amplitudes at 3 and 7 seconds after stimulus offset) DMS Patients (Individual Data) Blue response Relative amplitude at maximum constriction, % 3 s after stimulus offset 7 s after stimulus offset Red response Relative amplitude at maximum constriction, % Ratio blue/red response (relative amplitude at max. constriction) Controls (n = 20) (M ± 1.96 SD) 1 2 3 4 5 28.06* 38.67* 40.56* 49.12 47.70* 58.3 ± 9.41 10.69* 7.79 22.96 12.89 27.66 24.00 28.92 25.69 34.84 28.52 26.2 ± 11.56 17.1 ± 12.94 3.64* 13.49* 23.29* 17.57* 21.09* 43.0 ± 10.78 7.71* 2.87* 1.74* 2.8* 2.26* 1.37 ± 0.27 *Outside the normal distribution provided by the control subjects (mean ± 1.96 SD). DMS, dorsal midbrain syndrome; M, mean; s, seconds; SD, standard deviation. 250 Kelbsch et al: J Neuro-Ophthalmol 2017; 37: 247-252 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution DISCUSSION The main finding of our study was that pupil responses to 4 seconds of bright blue stimuli were less affected than to red stimuli in patients with DMS. We demonstrated a smaller reduction of the maximal relative constriction amplitude for blue compared with red stimulation (reduction of 30% [blue], 63% [red] compared with normal; significantly higher ratios blue/red for all patients outside the 1.96 SD of the normal cohort) with a preserved PIPR after blue stimulation. Furthermore, the latency time was prolonged. These results indicate that the melanopsin-mediated responses of ipRGCs are relatively preserved in patients with DMS. IpRGCs are not a single receptor class but differentiate into several subtypes projecting to numerous brain regions. In mice, 5 subtypes have been characterized (19,30,31). M1 subtype cells are believed to contribute to the pupil light reflex through the olivary pretectal nucleus and control the circadian rhythm through the suprachiasmatic nucleus, whereas non-M1 cells project to the lateral geniculate nucleus being involved in a rudimentary, low-acuity visual function (19). In addition, they project to target structures throughout the brain including the activity and sleep/wake status or nociception (19). To the best of our knowledge, in humans, only 2 morphological types of melanopsinexpressing RGCs have been documented. They are believed to generate similar synaptical (rod-driven and cone-driven) and melanopsin-mediated light responses, receive inputs from bipolar cells and amacrine cells, and project to the olivary pretectal nucleus and lateral geniculate nucleus. Their functional differences remain uncertain (14,31,32). In explaining our results, we hypothesize that a pupillary pathway circumvents the dorsal midbrain and is mediated by ipRGCs. Supportive evidence can be found in our patient cohort. Patient 1 had a relatively new lesion in the dorsal midbrain (3 months), whereas the other patients were treated several years previously (Table 1). In patient 1, the red response was the most affected of all subjects (nearly absent red response) but still showed a good blue response and PIPR. Possibly, in the other 4 patients, over the years, some recovery or reorganization occurred, leading to a better red response. Correspondingly, the time to maximum constriction was prolonged for both red and blue stimulation, and the shorter time to maximum constriction for red compared with blue stimulation that could be observed in the control group was no longer seen in the DMS group. These findings suggest that the pupil responses in DMS patients were not primarily traversing the "normal" rod/cone pathway. If there are 2 pupillary pathways, determining the contribution of each to the normal human pupillary light reflex is a major challenge. Possibly, ipRGCs facilitate the parasympathetically mediated pupillary light reaction by inhibiting its counterpart, the central sympathetic system. Partial sympathetic impairment in patients with DMS has been postulated based on the observation of asymmetric Kelbsch et al: J Neuro-Ophthalmol 2017; 37: 247-252 pupillary responses instead of an immediate dilation after sudden auditory stimuli in some DMS patients (28). In addition, preserved pupil grating response and pupil color response in patients with dorsal midbrain damage are considered to be mediated by central sympathetic disinhibition (29). Alternatively, it may be that the pupillary pathway through the dorsal midbrain of our patients was impaired, but not completely interrupted. In that case, however, red and blue pupillary responses would be expected to be preserved equally, but such was not the case. This observation would require a spatially inhomogeneous distribution of blue and red pupillary projections in the dorsal midbrain with a selectively more pronounced disturbance of the red projections in typical DMS. One could imagine that the blue projections of melanopsinmediated origin might enter more ventrally into the pretectal nucleus than the red projections of rod/conemediated origin. This might lead to greater damage to the red vs blue stimulation pathway in typical DMS analog to pupillary light-near dissociation. We recognize limitations of our study. We had a small sample size of only 5 patients with DMS. Patient 5 had mild, temporal optic disc pallor. This could have altered the pupil responses to both red and blue light stimulation. Future studies are required to verify our findings. Animal models targeting melanopsin through retrograde/anterograde labeling could be helpful. Neurophysiologic studies including functional MRI and magnetoencephalography also might assist in detection of alternative pupillary pathways. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: H. Wilhelm, B. Wilhelm, T. Peters, C. Kelbsch, F. Maeda, and T. Strasser; b. Acquisition of data: F. Maeda, C. Kelbsch, and H. Wilhelm; c. Analysis and interpretation of data: F. Maeda, C. Kelbsch, H. Wilhelm, B. Wilhelm, T. Strasser, and T. Peters. Category 2: a. Drafting the manuscript: F. Maeda and C. Kelbsch; b. Revising it for intellectual content: H. Wilhelm, B. Wilhelm, T. Strasser, and T. Peters. Category 3: a. Final approval of the completed manuscript: H. Wilhelm, B. Wilhelm, T. Peters, C. Kelbsch, F. Maeda, and T. Strasser. 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Kelbsch et al: J Neuro-Ophthalmol 2017; 37: 247-252 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.