This research was funded by LC Industries Postdoctoral research fellowship to RR and Bosma Enterprises Postdoctoral research fellowship to AK. The authors would like to thank Drs. Laura Walker and Donald Fletcher for their valuable suggestions and help in subject recruitment.

All the procedures and protocol described below were reviewed and approved by the institutional review board of Wichita State University, Wichita, Kansas. Informed consent was obtained from all the participants.
1. Participant selection
<ol>
	<li>Recruited participants with normal vision (n=5, 4 females, mean &#177; SE: 39.8 &#177; 2.6 years), and with central vision loss (n=15, 11 females, 78.3 &#177; 2.3 years) due to macular degeneration (age-related/juvenile). Note that grossly different...

<ol>
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W., Naber, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Eye+tracking+under+dichoptic+viewing+conditions:+a+practical+solution.">Eye tracking under dichoptic viewing conditions: a practical solution.</a> Behavior Research Methods. 49 (4), 1303-1309 (2017).</li><li>Qian, C. S., Brascamp, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+build+a+dichoptic+presentation+system+that+includes+an+eye+tracker.">How to build a dichoptic presentation system that includes an eye tracker.</a> Journal of Visualized Experiments. (127), (2017).</li><li>Raveendran, R. N., Bobier, W. R., Thompson, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Binocular+vision+and+fixational+eye+movements.">Binocular vision and fixational eye movements.</a> Journal of Vision. 19 (4), 1-15 (2019).</li><li>. Binocular vision and fixational eye movements Available from: <a target="_blank" href="https://uwspace.uwaterloo.ca/handle/10112/12076">https://uwspace.uwaterloo.ca/handle/10112/12076</a> (2017)</li><li>. Fixational eye movements in strabismic amblyopia Available from: <a target="_blank" href="https://uwspace.uwaterloo.ca/handle/10012/7478">https://uwspace.uwaterloo.ca/handle/10012/7478</a> (2013)</li><li>Maiello, G., Chessa, M., Solari, F., Bex, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simulated+disparity+and+peripheral+blur+interact+during+binocular+fusion.">Simulated disparity and peripheral blur interact during binocular fusion.</a> Journal of Vision. 14 (8), (2014).</li><li>Maiello, G., Harrison, W. J., Bex, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monocular+and+binocular+contributions+to+oculomotor+plasticity.">Monocular and binocular contributions to oculomotor plasticity.</a> Scientific Reports. 6, (2016).</li><li>Maiello, G., Kwon, M. Y., Bex, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+binocular+eye-hand+coordination+in+normal+vision+and+with+simulated+visual+impairment.">Three-dimensional binocular eye-hand coordination in normal vision and with simulated visual impairment.</a> Experimental Brain Research. 236 (3), 691-709 (2018).</li><li>Agaoglu, S., Agaoglu, M. N., Das, V. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Motion+Information+via+the+Nonfixating+Eye+Can+Drive+Optokinetic+Nystagmus+in+Strabismus.">Motion Information via the Nonfixating Eye Can Drive Optokinetic Nystagmus in Strabismus.</a> Investigative Opthalmology &amp; Visual Science. 56 (11), 6423 (2015).</li><li>Erkelens, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fusional+limits+for+a+large+random-dot+stereogram.">Fusional limits for a large random-dot stereogram.</a> Vision Research. 28 (2), 345-353 (1988).</li><li>Seiple, W., Szlyk, J. P., McMahon, T., Pulido, J., Fishman, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Eye-movement+training+for+reading+in+patients+with+age-related+macular+degeneration.">Eye-movement training for reading in patients with age-related macular degeneration.</a> Investigative Ophthalmology and Visual Science. 46 (8), 2886-2896 (2005).</li><li>Aguilar, C., Castet, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gaze-contingent+simulation+of+retinopathy:+Some+potential+pitfalls+and+remedies.">Gaze-contingent simulation of retinopathy: Some potential pitfalls and remedies.</a> Vision Research. 51 (9), 997-1012 (2011).</li><li>Pratt, J. D., Stevenson, S. B., Bedell, H. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scotoma+Visibility+and+Reading+Rate+with+Bilateral+Central+Scotomas.">Scotoma Visibility and Reading Rate with Bilateral Central Scotomas.</a> Optom Vis Sci. 94 (31), 279-289 (2017).</li><li>Babu, R. J., Clavagnier, S., Bobier, W. R., Thompson, B., Hess, R. F., PGH, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regional+Extent+of+Peripheral+Suppression+in+Amblyopia.">Regional Extent of Peripheral Suppression in Amblyopia.</a> Investigative Opthalmology &amp; Visual Science. 58 (4), 2329 (2017).</li><li>Ebenholtz, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Motion+Sickness+and+Oculomotor+Systems+in+Virtual+Environments.">Motion Sickness and Oculomotor Systems in Virtual Environments.</a> Presence: Teleoperators and Virtual Environments. 1 (3), 302-305 (1992).</li></ol>

The proposed method of measuring eye movements in dichoptic viewing condition has many potential applications. Assessing binocular visual fields in participants with central vision loss that is demonstrated here is one such application. We used this method to assess binocular visual field in fifteen participants with central vision loss to study how binocular viewing influences the heterogeneous central visual field loss.
The most important step in the protocol is positioning (distance from ey...

Macular degeneration is generally a bilateral condition affecting central vision and the pattern of visual loss can be heterogeneous. The central visual loss could be either symmetrical or asymmetrical between two eyes1. Currently, there are several techniques available to assess the central visual field in macular degeneration. The Amsler grid chart contains a grid pattern that can be used to manually screen central visual field. Automated perimeters (e.g., Humphrey visual field analyzer) present light flashes of varying brightness and sizes in a standardized ganzfeld bowl to probe the visual field. Gaze-contingent microperimetry presents visual stimulus on an LCD display. Micro-perimeters can compensate micro-eye movements by tracking a region of interest on the retina. Micro-perimeters can probe local regions in the central retina for changes in function but can test only one eye at a time. Consequently, micro-perimetric testing cannot explain how the heterogeneous defects in each eye affect the binocular interaction and real-world function. There is an unmet need for a method to reliably assess visual fields in a viewing condition that closely approximates real-world viewing. Such an assessment is necessary to understand how the visual field defect of one eye affects/contributes to the binocular visual field defect. We propose a novel method for assessing central visual field in people with central visual loss under dichoptic viewing condition (i.e., when visual stimuli are independently presented to each of the two eyes).
To measure visual fields reliably, fixation must be maintained at a given locus. Therefore, it is important to combine the eye-tracking and dichoptic presentation for binocular assessment. However, combining these two techniques can be challenging due to interference between the illuminating systems of the eye-tracker (e.g., infrared LEDs) and the optical elements of the dichoptic presenting systems (e.g., mirrors of haploscope or prisms of stereoscopes). Alternative options are to use an eye-tracking technique that does not interfere with the line of sight (e.g., scleral coil technique) or an eye-tracker that is integrated with goggles2. Though each method has its own benefits, there are disadvantages. The former method is considered invasive and can cause considerable discomfort3 and the latter methods have low temporal resolutions (60 Hz)4. To overcome these issues, Brascamp &#38; Naber (2017)5 and Qian &#38; Brascamp (2017)6 used a pair of cold mirrors (which transmitted infrared light but reflected 95% of the visible light) and a pair of monitors on either side of the cold mirrors to create a dichoptic presentation. Infrared video-based eye-tracker was used to track eye movements in the haploscope setup7,8.
However, using a haploscope-type dichoptic presentation has a drawback. The center of rotation of the instrument (haploscope) is different from the center of rotation of the eye. Therefore, additional calculations (as described in Appendix &#8211; A of Raveendran (2013)9) are required for proper and accurate measurements of eye movements. In addition, the planes of accommodation and vergence must be aligned (i.e., demand for accommodation and vergence must be the same). For example, if the working distance (total optical distance) is 40 cm, then the demand for accommodation and vergence is 2.5 diopters and 2.5-meter angles, respectively. If we align the mirrors perfectly orthogonal, then the haploscope is aligned for distant viewing (i.e., required vergence is zero), but the required accommodation is still 2.5D. Therefore, a pair of convex lenses (+2.50 diopters) must be placed between the eye and mirror arrangement of haploscope to push the plane of accommodation to infinity (i.e., required accommodation is zero). This arrangement necessitates more space between the eye and mirror arrangement of haploscope is required, which takes us back to the difference in centers of rotation. The issue of aligning planes of accommodation and vergence can be minimized by aligning the haploscope to the near viewing such that both the planes are aligned. However, this requires measurement of inter-pupillary distance for every participant and the corresponding alignment of haploscope mirrors/stimulus presenting monitors.
In this paper, we introduce a method to combine infrared video-based eye-tracking and dichoptic stimulus presentation using wireless 3D shutter glasses and 3D-ready monitors. This method does not require any additional calculations and/or assumptions like those used with the haploscopic method. Shutter glasses have been used in conjunction with eye trackers for understanding binocular fusion10, saccadic adaptation11, and eye-hand coordination12. However, it should be noted that stereo-shutter glasses used by Maiello and colleagues10,11,12 were the first-generation shutter glasses, which were connected through a wire to synchronize with the monitor refresh rate. Moreover, the first-generation shutter glasses are commercially unavailable now. Here, we demonstrate the use of commercially available second-generation wireless shutter glasses (Table of Materials) to present dichoptic stimulus and reliably measure monocular and binocular eye-movements. Additionally, we demonstrate a method to assess monocular/binocular visual fields in subjects with central visual field loss. While dichoptic presentation of visual stimulus enables monocular and binocular assessment of visual fields, binocular eye tracking under dichoptic viewing condition facilitates visual fields testing in a gaze-controlled paradigm.

<table>
	<tbody>
		<tr>
			<td>3D monitor</td>
			<td>Benq</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 500 
			https://zowie.benq.com/en/product/monitor/xl/xl2720.html</td>
		</tr>
		<tr>
			<td>3D shutter glass</td>
			<td>NVIDIA</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 300 
			https://www.nvidia.com/object/product-geforce-3d-vision2-wireless-glasses-kit-us.html</td>
		</tr>
		<tr>
			<td>Chin/forehead rest</td>
			<td>UHCO</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 750 
			https://www.opt.uh.edu/research-at-uhco/uhcotech/headspot/</td>
		</tr>
		<tr>
			<td>Eyetracker</td>
			<td>SR Research</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 27,000 
			https://www.sr-research.com/eyelink-1000-plus/</td>
		</tr>
		<tr>
			<td>IR reflective patch</td>
			<td>Tactical</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 10 
			https://www.empiretactical.org/infrared-reflective-patches/tactical-infrared-ir-square-patch-with-velcro-hook-fastener-1-inch-x-1-inch</td>
		</tr>
		<tr>
			<td>MATLAB Software</td>
			<td>Mathworks</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): 2150 
			https://www.mathworks.com/pricing-licensing.html</td>
		</tr>
		<tr>
			<td>Numerical Keypad</td>
			<td>Amazon</td>
			<td>CP001878 (model), B01E8TTWZ2 (ASIN)</td>
			<td>Approximate Cost (in USD): 15 
			https://www.amazon.com/Numeric-Jelly-Comb-Portable-Computer/dp/B01E8TTWZ2</td>
		</tr>
		<tr>
			<td>Psychtoolbox - Add on</td>
			<td>Freeware</td>
			<td>NA</td>
			<td>Approximate Cost (in USD): FREE 
			http://psychtoolbox.org/download.html</td>
		</tr>
		<tr>
			<td>Tripod (Dekstop)</td>
			<td>Manfrotto</td>
			<td>MTPIXI-B (model), B00D76RNLS (ASIN)</td>
			<td>Approximate Cost (in USD): 30 
			https://www.amazon.com/dp/B00D76RNLS</td>
		</tr>
	</tbody>
</table>

assessing binocular central visual field and binocular eye movements in a dichoptic viewing condition

Macular degeneration typically results in heterogeneous binocular central visual defects. Currently available approaches to assess central visual field, like the microperimetry, can test only one eye at a time. Therefore, they cannot explain how the defects in each eye affect the binocular interaction and real-world function. Dichoptic stimulus presentation with a gaze-controlled system could provide a reliable measure of monocular/binocular visual fields. However, dichoptic stimulus presentation and simultaneous eye-tracking are challenging because optical devices of instruments that present stimulus dichoptically (e.g., haploscope) always interfere with eye-trackers (e.g., infrared video-based eye-trackers). Therefore, the goals were 1) to develop a method for dichoptic stimulus presentation with simultaneous eye-tracking, using 3D-shutter glasses and 3D-ready monitors, that is not affected by interference and 2) to use this method to develop a protocol for assessing central visual field in subjects with central vision loss. The results showed that this setup provides a practical solution for reliably measuring eye-movements in dichoptic viewing condition. In addition, it was also demonstrated that this method can assess gaze-controlled binocular central visual field in subjects with central vision loss.

The representative binocular eye-movement traces of one observer with normal binocular vision during two different viewing conditions is shown (Figure 4). Continuous tracking of eye movements was possible when both eyes viewed the stimulus (Figure 4A), and when the left eye viewed the stimulus with the right eye under an active shutter (Figure 4B). As evident from these traces, the proposed method does not impact the quality of eye-...

Watch this Scientific Journal Video about Assessing Binocular Central Visual Field and Binocular Eye Movements in a Dichoptic Viewing Condition at JoVE.com

Assessing Binocular Central Visual Field and Binocular Eye Movements in a Dichoptic Viewing Condition

Presented here is a protocol for assessing binocular eye movements and gaze-controlled central visual field screening in participants with central vision loss.

Macular degeneration typically results in heterogeneous binocular central visual defects. Currently available approaches to assess central visual field, ...

Currently available methods for assessing central visual field are monocular. We use dichoptic stimuli presentation with the gaze control system for a reliable monocular and binocular visual field assessment. This method utilizes 3D-ready monitor and 3D shutter glasses for dichoptic stimuli presentation which provides simpler and more straightforward approaches than other methods, example using a haploscope.Demonstrating the procedure of testing will be Dr.Guler Arsal, a postdoctoral research associate at the Envision Research Institute. Before beginning an experiment, select a pair of wireless 3D active shutter glasses that can be synced with any 3D-ready monitor. For the shutter glasses to be active, there should be no interference between the infrared transmitter and the infrared receiver on the nose bridge of the shutter glasses.Display all of the visual stimuli on a 3D monitor at a 1920 by 1080 pixels, 144 Hertz resolution. For the monitor and the 3D glasses to work seamlessly, ensure that the appropriate drivers are installed. Place a table-mounted infrared video-based eye tracker that is capable of measuring eye movements at a 1, 000 Hertz sampling rate on the table next to the monitor and place a seat for the participant 100 centimeters from the monitor.Use a tripod to set up the eye tracker camera 20 to 30 centimeters from where the participant will be seated and use an infrared reflective patch to avoid interference between the infrared illumination of the eye tracker and the infrared system of the shutter glasses. Use commercially available software to integrate the shutter glasses with the 3D-ready monitor for the dichoptic presentation of visual stimuli to control the eye tracker. Clamp a tall wide chin and forehead rest to an adjustable table to allow comfortable positioning of the participant once the shutter glasses are on.Place the infrared reflective patch below the sensor and deactivate the light boost option in the 3D-ready monitor to minimize any leakage of the luminance information, then increase the strength of the infrared LEDs of the eye tracker to 100%from the default 50%in the software. A few minutes before the participant arrives, check that the eye tracker and host computer are on and confirm that the computer is connected to the eye tracker. Then check the synchronization accuracy of the display.When the participant arrives, have them sit with their head and chin in the rest and ask them to put on the 3D active shutter glasses. When the participant is comfortable, initiate the program that runs the main experiment from the appropriate interface. When prompted by the program, enter the participant information and save the output data file in a data folder with a unique filename.When a gray screen with instructions such as press Enter to toggle camera, press C to calibrate, press V to validate appears on the screen, adjust the camera of the eye tracker to align with the participant's pupil. For eye tracker calibration, initiate the calibration in the software and instruct the participant to follow the target by moving their eyes, but not their head, and to look at the center of the target. If the calibration is successful, initiate the validation and instruct the participant to once again follow the target with their eyes only while looking at the center of the target.Then read the results of the validation step on the screen. Once a good fair calibration and validation of the eye tracker has been achieved, initiate the drift correction and instruct the participant to look at the central fixation target while holding their eyes as steady as possible. Upon completion of the drift correction, inform the participant that they need to keep both eyes open during the entire testing, to hold the fixation at the central fixation target, and to press Enter in response to any white light observed.Instruct the participant not to search for new white lights and to not move their eyes and that the lights can appear at any location on the screen. At the end of the visual field experiment, the screen will display the result of the testing, differentially highlighting the seen and not seen locations. Although all of the visual field and eye movement data will be saved automatically for post-hoc analysis, be sure to confirm that the files have been saved before quitting the platform running the experiment.Here, the representative binocular eye movement traces of one observer with normal binocular vision during two different viewing conditions are shown. Continuous tracking of eye movements is possible when both eyes view the stimulus and when the left eye views the stimulus with the right eye under an active shutter. As evident, this method does not impact the quality of eye movement measurement and can measure eye movements for even long duration experiments.As observed, the method can be used to reliably measure eye movements even in challenging participants with central vision loss. Indeed, an important application of this method is screening the central visual field in subjects with and without central vision loss. The method provides a way to document the impact of central vision loss in a real world viewing with both eyes open as for this representative observer in which binocular advantage was observed.A successful synchronization of 3D-ready monitor and the 3D shutter glasses with the eye tracker can be achieved by strategically placing the infrared reflective patch. Although we demonstrated as a single visual field only, this method can be expanded to measure the threshold at each retinal location to study the monocular and binocular visual field deficits.

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4.3K visualizações.  Envision Research Institute. Currently available methods for assessing central visual field are monocular. We use dichoptic stimuli presentation with the gaze control system for a reliable monocular and binocular visual field assessment. This method utilizes 3D-ready monitor and 3D shutter glasses for dichoptic stimuli presentation which provides simpler and more straightforward approaches than other methods, example using a haploscope.Demonstrating the procedure of testing will be Dr.Guler Arsal, a postdoctoral r...