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Mapping the Binocular Scotoma in Macular Degeneration

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Journal of Vision (2021) 21(3):9, 1–12 1 Mapping the binocular scotoma in macular degeneration Smith-Kettlewell Eye Research Institute, San Francisco, Cécile Vullings CA, USA Smith-Kettlewell Eye Research Institute, San Francisco, Preeti Verghese CA, USA When the scotoma is binocular in macular degeneration where cortical processes perceptually complete missing (MD), it often obscures objects of interest, causing information by extrapolating the background (Zur & individuals to miss information. To map the binocular Ullman, 2003), although this challenge has not been scotoma as precisely as current methods that map the addressed under binocular viewing and it is unclear monocular scotoma, we propose an iterative eye-tracker how the nature of the stimulus affects this phenomenon method. Study participants included nine individuals (Cohen, Lamarque, Saucet, Provent, Langram, & with MD and four age-matched controls. We measured LeGargasson, 2003). the extent of the monocular scotomata using a scanning The binocular scotoma results from an overlap of the laser ophthalmoscope/optical coherence tomography two monocular scotomata and determines functional (SLO/OCT). Then, we precisely mapped monocular and vision in the real world. The residual vision outside binocular scotomata with an eye tracker, while fixation the scotoma along with factors, such as where it is was monitored. Participants responded whenever they placed with respect to the eccentric fixation locus, detected briefly flashed dots, which were first presented on a coarse grid, and then at manually selected points to determines performance in tasks including eye-hand refine the shape and edges of the scotoma. Monocular coordination (e.g. Verghese, Tyson, Ghahghaei, & scotomata measured in the SLO and eye tracker are Fletcher, 2016), navigation (e.g. Aspinall, Borooah, highly similar, validating the eye-tracking method for Alouch, Roe, Laude, Gupta, Gupta, Montarzino, scotoma mapping. Moreover, all participants used & Dhillon, 2014), facial recognition (e.g. Bernard & clustered fixation loci corresponding to their dominant Chung, 2016), visual search (e.g. Van der Stigchel, preferred fixation locus. Critically, for individuals with Bethlehem, Klein, Berendschot, Nijboer, & Dumoulin, binocular scotomata, the binocular map from the eye 2013), and reading (see Chung, 2020 for a review). tracker was consistent with the overlap of the Therefore, directly measuring the location and extent of monocular scotoma profiles from the SLO. Thus, the binocular scotoma is crucial for evaluating residual eye-tracker-based perimetry offers a reliable and functional vision when observers naturally interact sensitive tool for measuring both monocular and with the world. Importantly, a direct measure of the binocular scotomata, unlike the SLO/OCT that is limited binocular scotoma addresses two critical concerns with to monocular viewing. using monocular measurements to predict binocular function. The binocular scotoma can be estimated from monocular maps if the alignment of the two eyes is Introduction known. Although studies have reported that under binocular viewing, gaze in the worse eye is often Macular degeneration (MD) affects the central part aligned with the gaze of the fixation locus in the of the retina at and around the fovea, resulting in a better eye (Kabanarou, Crossland, Bellmann, Rees, scotoma. When MD is present in both eyes, it can Culham, & Rubin, 2006; Tarita-Nistor, Eizenman, create a binocular scotoma that obscures objects in the Landon-Brace, Markowitz, Steinbach, & González, central visual field and lead to the development ofa 2015), we make no assumptions about the alignment of new locus for fixation (e.g. Timberlake, Mainster, Webb, gaze. Additionally, binocular rivalry suppression often Hughes, & Trempe, 1982; Von Noorden & Mackensen, occurs during monocular viewing, particularly when 1962). Individuals are often not aware of the location of the dominant eye is covered (Ellingham, Waldock, their binocular scotoma, which can create difficulties in & Harrad, 1993), and can transiently lead to loss tasks of daily living (Fletcher, Schuchard, & Renninger, of vision and impact the estimation of a monocular 2012; Safran & Landis, 1999). This lack of awareness scotoma map. By directly measuring the functional has been attributed to the phenomenon of filling-in, scotoma under binocular viewing conditions, we Citation: Vullings, C., & Verghese, P. (2021). Mapping the binocular scotoma in macular degeneration. Journal of Vision, 21(3):9, 1–12, https://doi.org/10.1167/jov.21.3.9. https://doi.org/10.1167/jov.21.3.9 Received November 20, 2020; published March 5, 2021 ISSN 1534-7362 Copyright 2021 The Authors Downloaded from jov.arvojournals.orgThis work ison licensed 03/08/2021 under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. Journal of Vision (2021) 21(3):9, 1–12 Vullings & Verghese 2 avoid potential confounds of monocular viewing and the possibility of misalignment between the Materials and methods eyes. Presently, monocular visual field-testing methods, Participants such as automated perimetry in the Humphrey Field Analyzer, can determine the coarse boundary of Nine adults with MD (56–89 years old, 3 women) a monocular scotoma. Finer spatial detail of the and four age-matched controls (58–74 years old, monocular scotoma can be obtained with manual 3 women) participated in this research. Control selection of points for microperimetry in the scanning participants (C) had normal or corrected-to-normal laser ophthalmoscope (SLO) or other methods, such vision. Seven participants with MD had age-related as patient-tailored fundus-controlled perimetry (Pfau, MD in one or both eyes and two had Stargardt’s disease. Müller, Von der Emde, Lindner, Möller, Fleckenstein, Three participants had nonoverlapping monocular Holz, & Schmitz-Valckenberg, 2020). Spectral-domain scotomata (M) and six had a binocular scotoma (B). optical coherence tomography (OCT) methods that All participants with a binocular scotoma were referred determine the thickness of specific retinal layers can to us by the low-vision rehabilitation practice of also reliably identify visual field defects (e.g. Acton, Dr. Donald Fletcher at the Pacific Vision Foundation. Smith, Hood, & Greenstein, 2012; Brandao, Ledolter, All experimental procedures were approved by the Schötzau, & Palmowski-Worlfe, 2016; Nilforushan, Institutional Review Board of the Smith-Kettlewell Nassiri, Moghimi, Law, Giaconi, Coleman, Caprioli, Eye Research Institute and followed the tenets of the & Nouri-Mahdavi, 2012; Urata, Mariottoni, Jammal, Declaration of Helsinki. All participants gave informed Ogata, Thompson, Berchuck, Estrela, & Medeiros, written consent after an explanation of the nature 2020). Although these methods can map the region of and possible consequences of the study, and received the retinal lesion in detail, none of them can directly monetary compensation for their participation. determine the binocular field defect (but see Chung, Li, Agao˘ glu,˘ Tiruveedhula, & Roorda, 2020,who Apparatus used a custom-built binocular SLO with a maximum aperture of 10 degrees). The binocular scotoma Stimuli were generated using Psychophysics can be estimated approximately by the California Toolbox (Brainard, 1997; Pelli, 1997) for MATLAB Central Visual Field test (Mattingly Low Vision Inc., (MathWorks, Natick, MA, USA) and displayed on Escondido, CA, USA), which maps the binocular a large projection screen (40.36 × 30.27 degrees), scotoma in response to laser points flashed on a circular illuminated from behind by a Mitsubishi XD490U grid, while the patient fixates the center, although DLP projector. Participants were seated on a fixation is not monitored. Other studies have suggested height-adjustable chair in a darkened room facing the different ways to map the binocular scotoma with an center of the screen at a viewing distance of 1 m, with eye tracker (e.g. Janssen & Verghese, 2016; Shanidze their heads in a chin and forehead rest, to minimize & Verghese, 2019; Sullivan & Walker, 2015; Van der measurement errors. When viewing was binocular, only Stigchel et al., 2013; Wiecek, Jackson, & Bex, 2015) the position of the better/dominant eye was monitored but the spacing of probed regions was predetermined in the eye tracker. When viewing was monocular, the and not well-tailored to map individual scotoma viewing eye was tracked and the other eye was occluded. profiles. Eye movements were measured continuously with an In this study, we propose a novel eye-tracker-based infrared video-based eye tracking system (Eyelink, SR method to map the absolute binocular scotoma with Research Ltd., Ontario, Canada), sampled at 1000 precision and flexibility in a wide visual field, while Hz. Data were transferred, stored, and analyzed via carefully monitoring gaze position. The critical feature programs written in MATLAB running on a Windows of this method is the adaptive nature of the mapping computer. procedure based on previous measurements. We show The fixation cross (1 degree) and probe dots that monocular measurements in the eye tracker are (diameter 0.5 degrees), both with luminance of 283.6 highly similar to monocular microperimetry in the SLO cd/m2 were displayed on a background of luminance using a manual selection of test locations. Furthermore, 78.85 cd/m2. The Weber contrast of the cross and dots binocular measurements in the eye tracker provide a was 2.5967. direct estimate of the functional binocular scotoma,
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