Luis Durner

Advisors
Wolfgang Mehringer (M.Sc.), Prof. Dr.-med. Georg Michelson, Prof. Dr. Björn Eskofier

Duration
09/2018 – 02/2019

Abstract
Strabismus is a malfunction of the visuomotor system [1], meaning the eye movement is affected and therewith restricted. Young children with strabismus often develop a disease called amblyopia [2]. People with this disease usually have poor visual acuity on their amblyopic eye and therefore cannot develop a proper stereopsis, the ability to perceive depth. Especially for children it is very important to quickly look for a treatment to amblyopia because the human brain has its greatest neural plasticity during the first five years of life, the time, where stereopsis develops and improvs the best [3]. Over the last decades the primary treatment for amblyopia has been occlusion [3], where the healthy eye gets patched, so the brain is forced to accept the visual signals from the amblyopic eye. A big disadvantage of this treatment is the improvement of visual acuity at the expense of binocular vision [4]. Thus, it might happen that these patients experience a lifelong deprivation of stereovision [4]. Studies show that monocular blur degrades stereopsis more than seeing with two blurred eyes [5]. This led to new treatment approaches, so called dichoptic binocular treatments. This means instead of using only one eye and patching the other, the dichoptic training stimulates both eyes at the same time. The basis of dichoptic binocular treatment is binocular balancing [3]. The most important parts of balancing are to set the visual angle to compensate for any deviation of the eyes as well as to blur the images shown to the healthy eye. This sets both visual signals to the brain to an equal quality [3]. We assume that Virtual Reality (VR) is the perfect technology to implement such a binocular treatment environment because images can be presented to each eye separately. There already exist approaches for binocular treatment. The McGill University used red-green goggles to display the Game Tetris to patients with amblyopia dichoptically. Their first step was to align the patient’s eyes. This is done manually, without measuring the strabismus angle. Next, the level of suppression of the patient’s amblyopic eye gets quantified. This parameter is then used to suppress the images shown to the healthy eye. They showed the falling objects to the amblyopic eye at 100% contrast and the objects on the ground to the healthy eye with reduced contrast. Over time the contrast gets increased again. Therefore, both eyes are forced to work together, and vision can be improved in the lazy eye [6]. Another approach was developed by Vivid Vision. They utilize a Virtual Reality Headset to measure the strabismus angle and the suppression. These parameters are used for a VR game also developed by Vivid Vision. The task of the game is to navigate a spaceship, shown only to one eye, through rings, shown to the other eye [7]. Therewith, a pipeline is created which contains the measurement of the needed parameters as well as the treatment of amblyopia within one single VR device.

This bachelor thesis focuses on a VR tool to measure the strabismus angle for the process of binocular balancing but also for more depth information of the patient’s strabismus. The tool for measuring the strabismus angle shows stimuli for straight gaze as well as different lines of gaze. One stimulus will consist of four balls of which one has a different visual depth compared to the others having the same depth. The balls are shown to both eyes assuming no strabismus angle. This will lead to double vision in patients with strabismus. These patients will be able to move and rotate the image of the strabismic eye to superimpose the balls. Only with a corrected strabismus angle the patient will be able to see which of the balls has a different visual depth. Furthermore, the strabismus angle infers from the subject dependent amount of movement needed to superimpose the balls. By checking the angle of deviation at the center and in eight different positions around it, the tool can also be used to diagnose motor disorders of the eye muscles and possible torsions. This can help ophthalmologists to gain more information about the patient. It will help to monitor the progress of the patient over time and to provide an individually adapted vision to the patient to enhance the user experience. The proposed system will be evaluated with a study comparing an appropriate gold standard like the Hess screen test or the Lees screen test or equivalent. Parameters to evaluate include the average error of the measured angle of deviation and the task completion time as well as a system usability questionnaire.

References

1. J.T. Flynn. What Is Strabismus?. Strabismus A Neurodevelopmental Approach. Springer, New York, NY, 1.edition, 1991.
2. D. M. Levi. Visual Processing in Amblyopia: Human Studies. Strabismus, 14(1):11-19, 2006.
3. A.R. Connor & L.P. Tidburry. Stereopsis: are we assessing it in enough depth?. Clinical and Experimental Optometry, 101:485-495, 2018.
4. J. Li, B. Thompson, D. Deng, L.Y. Chan, M. Yu & R.F. Hess. Dichoptic training enables the adult amblyopic brain to learn. Current Biology, 23(8):308-309, 2013.
5. D.M. Levi, D.C. Knill & D. Bavelier. Stereopsis and amblyopia: A mini-review. Vision Research, 114:17-30, 2015.
6. J. Li, B. Thompson, C.S.Y Lam, D. Deng, L.Y.I. Chan, G. Maehara, G.C. Woo, M. Yu & R.F. Hess. The Role of Suppression in Amblyopia. Investigative Ophthalmology & Visual Research, 52(7):4169- 4176, 2011.
7. P. Žiak, A. Holm, J. Halička, P. Mojžiš & D. P. Piñero. Amblyopia treatment of adults with dichoptic training using the virtual reality oculus rift head mounted display: preliminary results. BMC Ophthalmology, 17:105, 2017