Najiya Sundus K. Meethal, M.Phil. (Optometry)

Research Associate, Medical Research Foundation, Chennai, India

Doctoral student, Dept. of Neuroscience, Erasmus MC, Rotterdam, The Netherlands

What is Eye-tracking technology?

I guess there is no possible conflict in believing ‘eyes are the windows to the soul’. Furthermore, they are the entryway to understand how humans gather, transfer and process information from the visual world, and what are the probable factors influencing their perception and cognition. These views were the reasons for exploring and learning ‘where we look’ since the early 1800s. During that era, eye movement studies were made using direct observations (naked-eye), which advanced and evolved (Figure 1) in the due course into contact-lens-based measurement method, and eventually into the modern non-intrusive eye trackers. Eye Tracking (ET) is a sensory technology that enables the detection and measurement of the gaze point (eye position and movement). The present-day technological expansions in the field of eye tracking permits us to gather an unrivalled insight regarding the human behaviour by relying on eye movements as one of the primary tools ¹.

Figure 1: (A and B) Edmund Huey’s (1908) apparatus used for recording eye movements during reading with a lever attached to a plaster eye-cup which moved a pen over a rotating smoked drum, the tracing on the drum was photographed and then engraved, (C) Guy Thomas Buswell’s device that used light beams which were reflected on readers’ eyes and recorded them on film, (D and E) Alfred L. Yarbus’s (1967) suction cups and eye movement recording device and a sample recording (F) Early head-mounted display device by Ivan Sutherland (1967).

(Image courtesy: Wade NJ. Pioneers of eye movement research. i-Perception. 2010 Aug;1(2):33-68.)

How and where eye-tracking works?

ET devices are either screen-based (remote) or glasses/head-mounted and consist of micro projectors and custom-designed camera that are integrated with advanced image-processing and mathematical algorithms. To describe the process of eye-tracking in a sentence: the projectors create a pattern of near-infrared light on the user’s eyes, the sensors capture high-frame-rate images, and the image algorithm process the reflection patterns, to calculate the eye’s position and gaze direction (Figure 2). ET technology is being used across a wide variety of disciplines including medicine, assistive/rehabilitation technologies, education/training, advertising & marketing, e-sports/virtual gaming, aviation, neuroarchitecture etc.

Figure 2: Commercially available ete tracking devices. (Image credit: Tobii Technology LLC  (https://www.tobii.com/group/about/this-is-eye-tracking/) and elisar.com)

Most common terminologies with respect to Eye-tracking

1. Gaze points: the basic output measures of interest that show what the eyes are looking at. For an example, an eye tracker device with a sampling/refresh rate of 60 Hz, collects 60 individual gaze points per second.
2. Fixation: If a series of gaze points is very close in time and/or in space then the gaze cluster constitutes a fixation (measure of visual attention), denoting a period where the eyes are sealed towards an object.
3. Area of Interest (AOI): is a tool to select regions of a displayed stimulus, and to extract and display metrics specifically for those regions. This includes how much time gap is between the stimulus onset and until the respondent looked at the region of interest, how much time did he/she spent in the region, the number of countable fixations etc.

Eye tracking technology in Ophthalmic care: a glimpse

​Medical science including the field of eye care has often been at the pole position of scientific developments as there is a clear impulse to improvise and innovate patient care. In ophthalmology, eye tracking technology-based innovations (navigation technology) are being instigated by focusing on ‘how to improve the existing care’. This focuses on learning the pattern and signs of dysfunctions in neuro/neuro-ophthalmic diseases, optimizing present diagnostic evaluations, including eye movement behaviour as an index that can complement other clinical evaluations, vision training/therapy during the rehabilitation phase, and teaching/training Eye Care Practitioners (ECPs) in interpreting diagnostic images. ​If I can specifically mention a few applications in eye care practice:

1. Functional diagnostics – Quantitative evaluation of eye movement behaviour (saccades and pursuits), pupil dynamics and in perimetry systems (Desktop-based, Mobile-based, Virtual Reality)
2. Ophthalmic imaging – Instruments such as OCT, OCTA (Angiography), microperimetry, fundus camera etc. use real-time ET technology for reducing motion artifacts and increasing signal-to-noise ratio in image acquisition as well as for proper orientation of captured zones of interest and accurate follow-up imaging
3. Ophthalmic surgery – ET is applied in refractive surgery, navigated retinal photocoagulation, and positioning guidance of Intraocular lenses (IOL) during cataract surgery etc.
4. Vison training/therapy & rehabilitation – ET based rehabilitative system in navigation training (including scanning behaviour) using real-life simulations
5. Medical education/training – Eye Movement Modeling Examples (EMME) in developing proficiency in students while interpreting visual images/diagnostic regions of interest by showing video-based playbacks of expert eye movements.

Conclusion

ET technology has immense possibilities in the field of ophthalmology and vision science. Hence it demands perspective long-term direction of research in developing innovative tools and interfaces for exploring its complete potential thereby extending its scope to revolutionize eye care practice.

References

1. Wade NJ. Pioneers of eye movement research. i-Perception. 2010 Aug;1(2):33-68.
2. Oyekunle R, Bello O, Jubril Q, Sikiru I, Balogun A. Usability Evaluation using Eye-Tracking on E-Commerce and Education Domains. Journal of Information Technology and Computing. 2020 Dec 31;1(1):1-3.
3. Brunyé TT, Drew T, Weaver DL, Elmore JG. A review of eye tracking for understanding and improving diagnostic interpretation. Cognitive research: principles and implications. 2019 Dec;4(1):1-6.
4. Boustany G, Itani AE, Youssef R, Chami O, Abu-Faraj ZO. Design and development of a rehabilitative eye-tracking based home automation system. In2016 3rd Middle East Conference on Biomedical Engineering (MECBME) 2016 Oct 6 (pp. 30-33). IEEE.

Author :-

Najiya Sundus K. Meethal (B.S., M.Phil.) has completed her Under graduation (B.S. optometry) and Post-graduation (M.Phil. in optometry) from Elite School of Optometry, Chennai in affiliation with BITS Pilani, India. Currently she is pursuing her doctoral studies at the Dept. of Neuroscience, Erasmus MC, Rotterdam, The Netherlands and also a research associate at Medical Research Foundation, Chennai. Her doctoral research falls under an Indo-Dutch collaboration and is focused on evaluating eye movement behaviour and pupillary dynamics in neurodegenerative diseases. She has successfully transferred her scientific findings into peer-reviewed publications and has presented her work at various national and international scientific platforms. She is dynamically involved in providing academic guidance and supervision in clinical as well research activities of undergraduate and post graduate optometry students at the Elite School of Optometry (ESO) and The Sankara Nethralaya Academy (TSNA), Chennai. She has bagged a few prestigious awards during her career as a researcher and academician. The credits include ‘Dr. Narasimhan memorial award (Medical Research Foundation) for the Best Research in Optometry’ (2017), ‘The Young clinical mentor award for the contribution towards optometric education and teaching in Elite School of Optometry, Chennai’ (2019), and ‘The Ruby Banik award for the best research in clinical ophthalmology instituted by Vision Research Foundation, Chennai (2020).