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 ages of the two groups was secondary to demographics of the subjects with central vision loss (age-related macular degeneration affects older subjects and is more prevalent in females). Further, the goal of this study was not comparing the two cohorts.</li>
</ol>
2. Preparation of the experiment
<ol>
	<li>Use a wireless 3D active shutter glasses (Table of Materials) 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 (a small pyramid-shaped black box) and the infrared receiver (sensor) on the nose bridge of the shutter glasses.</li>
	<li>Display all the visual stimuli on a 3D monitor (1920 x 1080 pixels, 144 Hz). For the monitor and the 3D glasses to work seamlessly, ensure that appropriate drivers are installed.</li>
	<li>Use a table-mounted infrared video-based eye-tracker (Table of Materials) that is capable of measuring eye movements at the sampling of 1000 Hz for this protocol. Separate the infrared illumination and camera of the eye-tracker use any tripod with adjustable height and angle (Table of Materials) to hold them firmly in place. Place the camera at a distance of 20-30 cm from the participant and place the screen at a distance of 100 cm from the participant.</li>
	<li>Use an infrared reflective patch (Table of Materials) to avoid the interference between infrared illumination of the eye-tracker and the infrared system of the shutter glasses (Figure 1, Right).</li>
	<li>Use commercially available software (Table of Materials) to integrate shutter glasses and 3D ready monitor for dichoptic presentation of visual stimuli to control the eyetracker.</li>
	<li>To stabilize the head movements, use a tall and wide chin and forehead rest (Table of Materials) and clamp it to an adjustable table. The wide dimension of the chin and forehead rest allows&#160;comfortable positioning of participants with the shutter glasses on. 
	NOTE: Figure 1 shows the setup for eye-tracking with dichoptic stimulus presentation using 3D shutter glasses and 3D-ready monitor. The infrared reflective patch was strategically placed below the infrared sensor on the nose bridge of 3D shutter glasses (Figure 1, Right).</li>
	<li>Minimize the leakage of luminance information by deactivating the light-boost option in the 3D ready monitor. The leakage of luminance information from one eye to the other eye is known as luminance leakage or crosstalk13. This is prone to occur&#160;with the stereoscopic displays in the high luminance conditions.</li>
	<li>Because of the shutters, the amount of infrared illumination (from the eye-tracking system) reaching the pupil can be significantly reduced13 &#8211; on an average, approximately 65% of luminance was reduced (Supplementary Table 1). To overcome this, increase the strength of the infrared LEDs of the eyetracker to 100% or (the maximum setting) from the default power setting. When using the infrared video-based eye-tracker (Table of Materials) change this setting in the &#8220;Illumination power&#8221; settings in the left bottom screen as shown in Figure 2.</li>
</ol>
3. Running the experiment
NOTE: The main experiment of this study was binocular eye tracking and screening of the central visual field using dichoptic stimulus. The central visual field screening was comparable to the visual field testing of commercially available instruments (Table of Materials). The physical properties of the visual stimulus such as luminance of the target (~22 cd/m2), luminance of the background (~10 cd/m2), size of the target (Goldmann III &#8211; 4 mm2), the visual field grid (Polar 3 grid with 28 points, Figure 3), and stimulus duration (200 ms) were identical to the visual field testing of commercially available instruments. Note that these luminance values were measured through shutter glasses when the shutter was ON (Supplementary Table 1). For the purposes of testing discussed here, the luminance of the stimulus was constant unlike visual field testing where the luminance of the stimulus is altered to obtain a detection threshold. In other words, the experiment employed supra-threshold screening and not thresholding. Therefore, the results of the screening were binary responses (stimuli seen or not seen) and not numerical values.
<ol>
	<li>Pre-experiment checks
	<ol>
		<li>A couple of minutes before the participant arrives for the testing, ensure that both eye tracker and the host computer (that runs the experiment) is turned on and confirm that the host computer is connected to the eyetracker.</li>
		<li>As a rule, confirm the synchronization accuracy (using platform specific commands) of the display before beginning the experiment.</li>
	</ol>
	</li>
	<li>Initiating the main experiment 
	NOTE:&#160;The steps below are very platform specific and is contingent on the script that runs the main experiment. See Supplementary Material&#160;that contain the samples of the codes used to design and run the experiment.
	<ol>
		<li>Initiate the program (See Supplementary Material - &#8216;ELScreeningBLR.m&#8217;) that runs the main experiment from the appropriate interface. When and if prompted by the program, enter the participant information (such as participant ID, test distance) that is needed to save the output data file in the data folder with a unique filename.</li>
		<li>A gray screen with instructions such as &#8220;Press Enter to toggle camera; Press C to calibrate, Press V to validate&#8221; will appear on the screen. At this stage, adjust the camera of the eye-tracker to align with the participant&#8217;s pupil as shown in Figure 2.</li>
	</ol>
	</li>
	<li>Eye-tracker calibration and validation
	<ol>
		<li>Initiate the calibration of the eye-tracker. Instruct the participants to follow the target by moving the eyes (and not head) and look at the center of the target.</li>
		<li>After the successful calibration, initiate the validation. Provide the same instructions as the calibration.</li>
		<li>Read the results of the validation step (usually displayed on the screen). Repeat the calibration and validation until &#8220;good/fair&#8221; (as recommended by the eyetracker manual) result is obtained.</li>
	</ol>
	</li>
	<li>Drift correction
	<ol>
		<li>Once the calibration and validation of the eye-tracker is done, initiate the drift correction.</li>
		<li>Instruct the participants to &#8220;look at the central fixation target and hold their eyes as steady as possible&#8221;. 
		NOTE: After the calibration, validation, and drift correction, the eye-tracking will be initiated simultaneously with the main experiment.</li>
	</ol>
	</li>
	<li>Visual field screening
	<ol>
		<li>Re-instruct/remind the participant about the task that he/she must do during the experiment. Ask subjects to keep both eyes open during the entire testing.</li>
		<li>For this visual field experiment, instruct them to hold the fixation at the central fixation target while responding to &#8220;any white light seen&#8221; by pressing the &#8220;enter&#8221; button in the response button (Figure 1, Table of Materials). Instruct them not to move the eyes and search for the new white lights. Also, remind them that the brief white lights can appear at any location on the screen. 
		NOTE: During visual field screening, the functioning of shutter glasses can be probed using monocular targets that can be fused to form a complete percept (See Supplementary Figure 2 &#8211; catch trials).</li>
		<li>Re-iterate the instruction to &#8220;hold fixation&#8221; several times throughout the experiment to ensure the fixation falls within the desired area. 
		NOTE: An audio feedback (like an error tone) can be used to alert loss of fixation (like eyes moved outside a tolerance window). When fixation lapses, reinstruct the participant to fixate only on the cross target. The visual stimuli presentation can be temporarily stopped until the participant brings the fixation back within the tolerance window (like central 2&#176;).</li>
		<li>At the end of the visual field experiment, the screen will display the result of the testing highlighting the seen and non-seen locations differently (like for example Figure 6).</li>
	</ol>
	</li>
	<li>Saving the data file
	<ol>
		<li>All the visual field data (say saved as &#8220;. mat&#8221; file) and eye-movement data (say saved as &#8220;.edf&#8221; file) will be saved automatically for post-hoc analysis. However, ensure that the files have been saved before quitting the program/platform running the experiment.</li>
	</ol>
	</li>
</ol>
4. Analysis
NOTE: The analysis of eye movement and visual field data can be performed in several ways and is contingent on the software used to run the experiment and data format of eye tracker&#8217;s output. The steps below are specific to the setup and the program (See Supplementary Materials).
<ol>
	<li>Eye movement analysis (post-hoc) 
	NOTE: The saved eye movements data file (EDF) is a highly compressed binary format, and it contains many types of data, including eye movement events, messages, button presses, and gaze position samples.
	<ol>
		<li>Convert EDF to ASC-II files using a translator program (EDF2ASC).</li>
		<li>Run &#8216;PipelineEyeMovementAnalysisERI.m&#8217; to initialize eye movement analysis and follow the instructions as noted in the code (See Supplementary Materials for the code script).</li>
		<li>Run &#8216;EM_plots.m&#8217;, to extract horizontal and vertical eye positions and to plot as shown in Figure 4 and Figure 5. 
		NOTE: Eye movement data can be further analyzed to compute fixation stability, detect microsaccades, etc. However, this is beyond the scope of the current paper.</li>
	</ol>
	</li>
	<li>Visual fields
	<ol>
		<li>To get the reports of visual field test, run &#8216;VF_plot.m&#8217;. 
		NOTE: All datasets pertaining to the visual field experiment such as points seen/not seen will be plotted as a visual field map as shown in Figure 6. If a point was seen, then it will be plotted as &#8220;green&#8221; filled square, otherwise a red filled square will be plotted. No post-hoc analysis for visual field data will be required.</li>
	</ol>
	</li>
</ol>

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	<li>Fletcher, D. C., Schuchard, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preferred+retinal+loci+relationship+to+macular+scotomas+in+a+low-vision+population.">Preferred retinal loci relationship to macular scotomas in a low-vision population.</a> Ophthalmology. 104 (4), 632-638 (1997).</li><li>Raveendran, R. N., Babu, R. J., Hess, R. F., Bobier, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+improvements+in+fixational+stability+in+strabismic+amblyopes+following+bifoveal+fixation+and+reduced+interocular+suppression.">Transient improvements in fixational stability in strabismic amblyopes following bifoveal fixation and reduced interocular suppression.</a> Ophthalmic &amp; Physiological Optics. 34, 214-225 (2014).</li><li>Nystr&#246;m, M., Hansen, D. W., Andersson, R., Hooge, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Why+have+microsaccades+become+larger?+Investigating+eye+deformations+and+detection+algorithms.">Why have microsaccades become larger? Investigating eye deformations and detection algorithms.</a> Vision Research. , (2014).</li><li>Raveendran, R. N., Babu, R. J., Hess, R. F., Bobier, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+improvements+in+fixational+stability+in+strabismic+amblyopes+following+bifoveal+fixation+and+reduced+interocular+suppression.">Transient improvements in fixational stability in strabismic amblyopes following bifoveal fixation and reduced interocular suppression.</a> Ophthalmic and Physiological Optics. 34 (2), (2014).</li><li>Brascamp, J. 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. 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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. 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The authors have nothing to disclose. Parts of the study presented here were presented as abstract titled &#8220;Binocular Central Visual Function in Macular Degeneration&#8221; in the annual meeting of American academy of Optometry 2019.

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&lt;br/&gt; 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&lt;br/&gt; 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&lt;br/&gt; 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&lt;br/&gt; 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&lt;br/&gt; 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&lt;br/&gt; 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&lt;br/&gt; 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&lt;br/&gt; 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&lt;br/&gt; 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-...

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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, ...

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4.4K Views.  Envision Research Institute. Presented here is a protocol for assessing binocular eye movements and gaze-controlled central visual field screening in participants with central vision loss.

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

VisualEyes: A Modular Software System for Oculomotor Experimentation

Eye movement studies have provided a strong foundation forming an understanding of how the brain acquires visual information in both the normal and dysfunctional brain.1 However, development of a platform to stimulate and store eye movements can require substantial programming, time and costs. Many systems do not offer the flexibility to program numerous stimuli for a variety of experimental needs. However, the VisualEyes System has a flexible architecture, allowing the operator to choose any background and foreground stimulus, program one or two screens for tandem or opposing eye movements and stimulate the left and right eye independently. This system can significantly reduce the programming development time needed to conduct an oculomotor study. The VisualEyes System will be discussed in three parts: 1) the oculomotor recording device to acquire eye movement responses, 2) the VisualEyes software written in LabView, to generate an array of stimuli and store responses as text files and 3) offline data analysis. Eye movements can be recorded by several types of instrumentation such as: a limbus tracking system, a sclera search coil, or a video image system. Typical eye movement stimuli such as saccadic steps, vergent ramps and vergent steps with the corresponding responses will be shown. In this video report, we demonstrate the flexibility of a system to create numerous visual stimuli and record eye movements that can be utilized by basic scientists and clinicians to study healthy as well as clinical populations.

Neural control and cognitive processes can be studied through eye movements. The VisualEyes software allows an operator to program stimuli on two computer screens independently using a simple, custom scripting language. The system can stimulate tandem eye movements (saccades and smooth pursuit) or opposing eye movements (vergence) or any combination.

Eye movement studies have provided a strong foundation forming an understanding of how the brain acquires visual information in both the normal and ...

Neuroscience

How to Build a Dichoptic Presentation System That Includes an Eye Tracker

The presentation of different stimuli to the two eyes, dichoptic presentation, is essential for studies involving 3D vision and interocular suppression. There is a growing literature on the unique experimental value of pupillary and oculomotor measures, especially for research on interocular suppression. Although obtaining eye-tracking measures would thus benefit studies that use dichoptic presentation, the hardware essential for dichoptic presentation (e.g. mirrors) often interferes with high-quality eye tracking, especially when using a video-based eye tracker. We recently described an experimental setup that combines a standard dichoptic presentation system with an infrared eye tracker by using infrared-transparent mirrors1. The setup is compatible with standard monitors and eye trackers, easy to implement, and affordable (on the order of US$1,000). Relative to existing methods it has the benefits of not requiring special equipment and posing few limits on the nature and quality of the visual stimulus. Here we provide a visual guide to the construction and use of our setup.

We recently proposed a method that allows dichoptic visual stimulus presentation and binocular eye tracking simultaneously1. The key is the combination of an infrared eye tracker and the corresponding infrared-transparent mirrors. This manuscript provides an in depth protocol for initial setup and everyday operation.

The presentation of different stimuli to the two eyes, dichoptic presentation, is essential for studies involving 3D vision and interocular suppression. ...

Central and Divided Visual Field Presentation of Emotional Images to Measure Hemispheric Differences in Motivated Attention

Two dominant theories on lateralized processing of emotional information exist in the literature. One theory posits that unpleasant emotions are processed by right frontal regions, while pleasant emotions are processed by left frontal regions. The other theory posits that the right hemisphere is more specialized for the processing of emotional information overall, particularly in posterior regions.
Assessing the different roles of the cerebral hemispheres in processing emotional information can be difficult without the use of neuroimaging methodologies, which are not accessible or affordable to all scientists. Divided visual field presentation of stimuli can allow for the investigation of lateralized processing of information without the use of neuroimaging technology. 
This study compared central versus divided visual field presentations of emotional images to assess differences in motivated attention between the two hemispheres. The late positive potential (LPP) was recorded using electroencephalography (EEG) and event-related potentials (ERPs) methodologies to assess motivated attention. Future work will pair this paradigm with a more active behavioral task to explore the behavioral impacts on the attentional differences found.

This study compared central versus divided visual field presentations of emotional images to assess differences in motivated attention between the two hemispheres. The late positive potential (LPP) was recorded using electroencephalography (EEG) and event-related potentials (ERPs) methodologies to assess motivated attention.

Two dominant theories on lateralized processing of emotional information exist in the literature. One theory posits that unpleasant emotions are processed ...

Monocular Visual Deprivation and Ocular Dominance Plasticity Measurement in the Mouse Primary Visual Cortex

Monocular visual deprivation is an excellent experimental paradigm to induce primary visual cortical response plasticity. In general, the response of the cortex to the contralateral eye to a stimulus is much stronger than the response of the ipsilateral eye in the binocular segment of the mouse primary visual cortex (V1). During the mammalian critical period, suturing the contralateral eye will result in a rapid loss of responsiveness of V1 cells to contralateral eye stimulation. With the continuing development of transgenic technologies, more and more studies are using transgenic mice as experimental models to examine the effects of specific genes on ocular dominance (OD) plasticity. In this study, we introduce detailed protocols for monocular visual deprivation and calculate the change in OD plasticity in mouse V1. After monocular deprivation (MD) for 4 days during the critical period, the orientation tuning curves of each neuron are measured, and the tuning curves of layer four neurons in V1 are compared between stimulation of the ipsilateral and contralateral eyes. The contralateral bias index (CBI) can be calculated using each cell&#39;s ocular OD score to indicate the degree of OD plasticity. This experimental technique is important for studying the neural mechanisms of OD plasticity during the critical period and for surveying the roles of specific genes in neural development. The major limitation is that the acute study cannot investigate the change in neural plasticity of the same mouse at a different time.

Here, we present detailed protocols for monocular visual deprivation and ocular dominance plasticity analysis, which are important methods for studying the neural mechanisms of visual plasticity during the critical period and the effects of specific genes on visual development.

Monocular visual deprivation is an excellent experimental paradigm to induce primary visual cortical response plasticity. In general, the response of the ...

Developmental Biology

Quantification of Oculomotor Responses and Accommodation Through Instrumentation and Analysis Toolboxes

Through the purposeful stimulation and recording of eye movements, the fundamental characteristics of the underlying neural mechanisms of eye movements can be observed. VisualEyes2020 (VE2020) was developed based on the lack of customizable software-based visual stimulation available for researchers that does not rely on motors or actuators within a traditional haploscope. This new instrument and methodology have been developed for a novel haploscope configuration utilizing both eye tracking and autorefractor systems. Analysis software that enables the synchronized analysis of eye movement and accommodative responses provides vision researchers and clinicians with a reproducible environment and shareable tool. The Vision and Neural Engineering Laboratory&#39;s (VNEL) Eye Movement Analysis Program (VEMAP) was established to process recordings produced by VE2020&#39;s eye trackers, while the Accommodative Movement Analysis Program (AMAP) was created to process the recording outputs from the corresponding autorefractor system. The VNEL studies three primary stimuli: accommodation (blur-driven changes in the convexity of the intraocular lens), vergence (inward, convergent rotation and outward, divergent rotation of the eyes), and saccades (conjugate eye movements). The VEMAP and AMAP utilize similar data flow processes, manual operator interactions, and interventions where necessary; however, these analysis platforms advance the establishment of an objective software suite that minimizes operator reliance. The utility of a graphical interface and its corresponding algorithms allow for a broad range of visual experiments to be conducted with minimal required prior coding experience from its operator(s).

VisualEyes2020 (VE2020) is a custom scripting language that presents, records, and synchronizes visual eye movement stimuli. VE2020 provides stimuli for conjugate eye movements (saccades and smooth pursuit), disconjugate eye movements (vergence), accommodation, and combinations of each. Two analysis programs unify the data processing from the eye tracking and accommodation recording systems.

Through the purposeful stimulation and recording of eye movements, the fundamental characteristics of the underlying neural mechanisms of eye movements ...

Bioengineering

Binocular Dynamic Visual Acuity in Eyeglass-Corrected Myopic Patients

Current clinical visual assessment mainly focuses on static vision. However, static vision may not sufficiently reflect real-life visual function as moving optotypes are frequently observed daily. Dynamic visual acuity (DVA) might reflect real-life situations better, especially when objects are moving at high speeds. Myopia impacts static uncorrected distance visual acuity, conveniently corrected with eyeglasses. However, due to peripheral defocus and prism effects, eyeglass correction might affect DVA. The present research demonstrates a standard method to examine eyeglass-corrected DVA in myopia patients, and aimed to explore the influence of eyeglass correction on DVA. 
Initially, standard subjective refraction was performed to provide the eyeglass prescription to correct the refractive error. Then, binocular distance vision-corrected DVA was examined using the object-moving DVA protocol. Software was designed to display the moving optotypes according to the preset velocity and size on a screen. The optotype was the standard logarithmic visual chart letter E and moves from the middle of the left to the right side horizontally during the test. Moving optotypes with randomized opening direction for each size are displayed. The subjects were required to identify the opening direction of the optotype, and the DVA is defined as the minimum optotype that subjects could recognize, calculated according to the algorithm of logarithmic visual acuity.
Then, the method was applied in 181 young myopic subjects with eyeglass-corrected-to-normal static visual acuity. Dominant eye, cycloplegic subjective refraction (sphere and cylinder), accommodation function (negative and positive relative accommodation, binocular cross-cylinder), and binocular DVA at 40 and 80 degrees per second (dps) were examined. The results showed that with increasing age, DVA first increased and then decreased. When myopia was fully corrected with eyeglasses, a worse binocular DVA was associated with more significant myopic refractive error. There was no correlation between the dominant eye, accommodation function, and binocular DVA.

The present research demonstrates a method to accurately examine dynamic visual acuity (DVA) in myopic subjects with eyeglass correction. Further analysis indicated that the closer the refraction state to emmetropia, the better the eyeglass-corrected binocular DVA is at both 40 and 80 degrees per second.

Current clinical visual assessment mainly focuses on static vision. However, static vision may not sufficiently reflect real-life visual function as ...

Medicine

Gaze-Contingent Framework for Studying and Training in Simulated Vision Loss

A Gaze-Contingent Display Framework for Perceptual Learning Research with Simulated Central Vision Loss

Macular degeneration (MD) is one of the leading causes of vision impairment in the Western world. Patients with MD tend to develop spontaneous eye movement strategies to compensate for their vision loss, including adopting a preferred retinal locus, or PRL, a spared peripheral region that they use more frequently to replace the damaged fovea. However, not all patients are successful in developing a PRL, and even when they do, it might take them months. Currently, no gold standard rehabilitative therapy exists, and MD research is further hindered by issues of recruitment, compliance, and comorbidity. To help address these issues, a growing body of research has used eye tracking-guided, gaze-contingent displays in a simulated central vision loss paradigm in individuals with intact vision. While simulated vision loss is qualitatively different than pathological central vision loss, our framework provides for a highly controlled model through which to study compensatory eye movements and test possible rehabilitation interventions in low vision. By developing a comprehensive framework, rather than relying on isolated and disconnected tasks, we create a cohesive environment where we can test larger-scale hypotheses, allowing us to examine interactions between tasks, assess training effects across multiple measures, and establish a consistent methodology for future research. Furthermore, participants in simulated central vision loss studies show similarities in their oculomotor compensatory behaviors compared to patients with MD. Here, we present a framework for conducting gaze-contingent studies related to simulated central vision loss. We emphasize the utilization of the framework to test behavioral and oculomotor performance of healthy individuals on a wide range of perceptual tasks encompassing different levels of visual processing. We also discuss how this framework can be adapted for training MD patients.

Development of a Gaze-Contingent Display Framework Designed for Perceptual and Oculomotor Research with Simulated Central Vision Loss

We present development of a gaze-contingent display framework designed for perceptual and oculomotor research simulating central vision loss. This framework is particularly adaptable for studying compensatory behavioral and oculomotor strategies in individuals experiencing both simulated and pathological central vision loss.

Macular degeneration (MD) is one of the leading causes of vision impairment in the Western world. Patients with MD tend to develop spontaneous eye ...

 Evaluating Stereopsis in Unilateral Amblyopia: A Comparative Study

Comparison of Three Clinical Stereoscopic Methods for Measuring Binocular Visual Function During Amblyopic Treatment in Unilateral Amblyopia

This study aimed to compare the measuring stereopsis results of unilateral amblyopia during amblyopic treatment by employing some of the most widely used clinical tests. Thirty-four individuals with previously untreated unilateral amblyopia, aged 8.4 &#177; 2.7 years, were included in the study. Monocular (best corrected visual acuity [BCVA] at distance) and binocular (including Titmus, Random-dot, and Frisby stereopsis) visual functions were measured at baseline and 2-month and 6-month visits after synthetical treatment.
We found that Titmus stereopsis was always significantly better than Random-dot stereopsis (p &#60; 0.001). Frisby stereopsis was also always significantly better than Random-dot stereopsis (p &#60; 0.001). However, there was no significant difference between Titmus stereopsis and Frisby stereopsis (p = 0.562). However, interestingly, there was no significant difference in the mean improvement of the three stereopsis methods from baseline to the 2-month visit, F = 1.158, p = 0.318.
Similarly, a significant difference was also lacking in the mean improvement of the three stereopsis methods from baseline to the 6-month visit, F = 0.302, p = 0.740. We conclude that there will be different results obtained from different stereopsis measuring methods used to measure amblyopia in patients. We recommend performing at least two types of stereoscopic measurements to evaluate each case of amblyopia. However, for observing therapeutic effects, each measurement method has the same performance for clinical results during amblyopic treatment.

Here, we present three common stereopsis measurement methods to measure patients with amblyopia and the comparison of the efficacy of different methods.

This study aimed to compare the measuring stereopsis results of unilateral amblyopia during amblyopic treatment by employing some of the most widely used ...

Cranial Nerves Exam I (I-VI)

Source:Tracey A. Milligan, MD; Tamara B. Kaplan, MD; Neurology, Brigham and Women&#39;s/Massachusetts General Hospital, Boston, Massachusetts, USA
During each section of the neurological testing, the examiner uses the powers of observation to assess the patient. In some cases, cranial nerve dysfunction is readily apparent: a patient might mention a characteristic chief complaint (such as loss of smell or diplopia), or a visually evident physical sign of cranial nerve involvement, such as in facial nerve palsy. However, in many cases a patient&#39;s history doesn&#39;t directly suggest cranial nerve pathologies, as some of them (such as sixth nerve palsy) may have subtle manifestations and can only be uncovered by a careful neurological exam. Importantly, a variety of pathological conditions that are associated with alterations in mental status (such as some neurodegenerative disorders or brain lesions) can also cause cranial nerve dysfunction; therefore, any abnormal findings during a mental status exam should prompt a careful and complete neurological exam.
The cranial nerve examination is applied neuroanatomy. The cranial nerves are symmetrical; therefore, while performing the examination, the examiner should compare each side to the other. A physician should approach the examination in a systematic fashion and go through the cranial nerves in their numerical order.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>I</td>
			<td>Olfactory</td>
			<td>Smell</td>
		</tr>
		<tr>
			<td>II</td>
			<td>Optic</td>
			<td>Visual acuity, afferent pupillary response</td>
		</tr>
		<tr>
			<td>III</td>
			<td>Oculomotor</td>
			<td>Horizontal eye movements (adduction), efferent pupillary response</td>
		</tr>
		<tr>
			<td>IV &#160;</td>
			<td>Trochlear</td>
			<td>Downward vertical eye movement, internal rotation of eye</td>
		</tr>
		<tr>
			<td>V &#160;&#160;</td>
			<td>Trigeminal&#160;&#160;&#160;</td>
			<td>Facial sensation, jaw movement</td>
		</tr>
		<tr>
			<td>VI &#160;</td>
			<td>Abducens</td>
			<td>Horizontal eye movement (abduction)</td>
		</tr>
		<tr>
			<td>VII</td>
			<td>Facial</td>
			<td>Facial movement and strength, taste, dampening of loud sounds, sensation; anterior wall of external ear canal</td>
		</tr>
		<tr>
			<td>VIII</td>
			<td>Acoustic</td>
			<td>Hearing, vestibular functioning</td>
		</tr>
		<tr>
			<td>IX</td>
			<td>Glossopharyngeal</td>
			<td>Movement of pharynx, sensation of pharynx, posterior tongue (including taste of posterior tongue), and most of ear canal</td>
		</tr>
		<tr>
			<td>X</td>
			<td>Vagal</td>
			<td>Movement and sensation of palate, pharynx, gag reflex, guttural sounds&#160;</td>
		</tr>
		<tr>
			<td>XI</td>
			<td>Spinal accessory</td>
			<td>Strength of sternocleidomastoids and trapezius muscles</td>
		</tr>
		<tr>
			<td>XII</td>
			<td>Hypoglossal</td>
			<td>Tongue protrusion and lateral movements</td>
		</tr>
	</tbody>
</table>
Table 1. The 12 Cranial Nerves and Their Basic Functions
Cranial nerve I (the olfactory nerve) is a purely sensory nerve that conveys the sense of smell, and is not routinely tested during most examinations. Cranial nerve II (the optic nerve) is the only cranial nerve that can be directly visualized as it exits from the central nervous system. Its axons convey visual information and compose the afferent limb of the pupillary reflex. Testing of the pupillary responses also assesses the function of cranial nerve III (the oculomotor nerve), parasympathetic fibers of which form the efferent limb of the pupillary reflex. Cranial nerve exam includes assessment of the extraocular movements, which are controlled by cranial nerves III, IV and VI. Cranial nerve III innervates the superior, medial, and inferior rectus muscles, as well as the inferior oblique muscle, which together function to move eyes medially and in the vertical plane. Cranial nerve IV (the trochlear nerve_ innervates the superior oblique muscles, which moves the eye downward and outward. Cranial nerve VI (the abducens nerve) innervates the lateral rectus muscles, which abducts the eyes. The function of the medial and lateral rectus muscles is straightforward: Lateral rectus is involved in abduction, meaning lateral movement along the horizontal plane. Medial rectus adducts moving the eye medially movement along the horizontal plane. The remaining muscles each causes movement in more than one direction and some combination of elevation/depression, abduction/adduction, intorsion/extorsion.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Muscle</td>
			<td>Innervation</td>
			<td>Primary action</td>
			<td>Secondary action</td>
			<td>Tertiary action</td>
		</tr>
		<tr>
			<td>Medial rectus</td>
			<td>CN III</td>
			<td>Adduction</td>
			<td>--</td>
			<td>--</td>
		</tr>
		<tr>
			<td>Superior rectus</td>
			<td>CN III</td>
			<td>Elevation</td>
			<td>Intortion</td>
			<td>Adduction</td>
		</tr>
		<tr>
			<td>Inferior rectus</td>
			<td>CN III</td>
			<td>Depression</td>
			<td>Extortion</td>
			<td>Adduction</td>
		</tr>
		<tr>
			<td>Inferior oblique</td>
			<td>CN III</td>
			<td>Extorsion</td>
			<td>Elevation</td>
			<td>Abduction</td>
		</tr>
		<tr>
			<td>Superior oblique</td>
			<td>CN IV</td>
			<td>Intorsion</td>
			<td>Depression</td>
			<td>Abduction</td>
		</tr>
		<tr>
			<td>Lateral rectus</td>
			<td>CN VI</td>
			<td>Abduction</td>
			<td>--</td>
			<td>--</td>
		</tr>
	</tbody>
</table>
Table 2. The function of the six extraocular muscles.
This first part of the cranial nerve exam concludes by testing cranial nerve V (the trigeminal nerve). This nerve has both motor and sensory components. It controls facial sensation, masticatory movements and forms the afferent limb of the corneal reflex. There are 3 major sensory branches of the trigeminal nerve - the ophthalmic, maxillary, and mandibular (also labeled V1, V2, and V3, respectively).

Anatomy and Physiology of the Cranial Nerves I -VI

Source:Tracey A. Milligan, MD; Tamara B. Kaplan, MD; Neurology, Brigham and Women&#39;s/Massachusetts General Hospital, Boston, Massachusetts, USA
During ...

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Physical Examinations III

Binocular Rivalry

Source: Laboratory of Jonathan Flombaum&#8212;Johns Hopkins University

Why do people have two forward-facing eyes? By presenting the brain with two ever so slightly different images it becomes possible to comprehend visual problems that are far more difficult to process through a single eye. Chief among these is the problem of 3-D perception, seeing the world in three dimensions, despite retinal inputs in only two dimensions.
What happens if each eye receives two completely different images? That does not happen in nature, to be sure, but it can be contrived in the laboratory in a set-up called binocular rivalry.
Binocular rivalry is a common laboratory paradigm for investigating the ways that the brain integrates information from two eyes, and in recent years, the mechanisms responsible for producing conscious experience.

Binocular Rivalry: Studying Visual Perception and Neural Correlates of Consciousness

Source: Laboratory of Jonathan Flombaum&#8212;Johns Hopkins University

Why do people have two forward-facing eyes? By presenting the brain with two ever ...