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.
