Testing Stereopsis in Children

Stereopsis develops very early in life and is thought to be present in a normally developing child by six months of age. In order to develop stereopsis, multiple components of visual development must be intact including visual acuity and bifoveal fixation. Stereopsis is the most sensitive way to assess sensory fusion but can be unreliable in very young age groups due to difficulty understanding the test or instructions. It is best to choose an option with global stereopsis (high level cortical stereo), as local stereopsis may overestimate ability due to available monocular cues. Global is created using random dot stereograms (RDS) – computer-generated patterns to create a stereoscopic form, while local contains line stereograms which create horizontal retinal image disparity giving the perception of depth. Stereopsis can be affected by strabismus, amblyopia, and other binocular vision dysfunctions that interfere with visual efficiency (especially in school-age children). The chapter discusses the most commonly used clinical tests of global and local stereopsis.

Transfer of Perceptual Learning From Local Stereopsis to Global Stereopsis in Adults With Amblyopia: A Preliminary Study

It has long been debated whether the analysis of global and local stereoscopic depth is performed by a single system or by separate systems. Global stereopsis requires the visual system to solve a complex binocular matching problem to obtain a coherent percept of depth. In contrast, local stereopsis requires only a simple matching of similar image features. In this preliminary study, we recruited five adults with amblyopia who lacked global stereopsis and trained them on a computerized local stereopsis depth task for an average of 12 h. Three out of five (60%) participants recovered fine global stereoscopic vision through training. Those who recovered global stereopsis reached a learning plateau more quickly on the local stereopsis task, and they tended to start the training with better initial local stereopsis performance, to improve more on local stereopsis with training, and to have less severe amblyopia. The transfer of learning from local stereopsis to global stereopsis is compatible with an interacting two-stage model.

Effects of stereopsis on vection, presence and cybersickness in head-mounted display (HMD) virtual reality

Stereopsis provides critical information for the spatial visual perception of object form and motion. We used virtual reality as a tool to understand the role of global stereopsis in the visual perception of self-motion and spatial presence using virtual environments experienced through head-mounted displays (HMDs). Participants viewed radially expanding optic flow simulating different speeds of self-motion in depth, which generated the illusion of self-motion in depth (i.e., linear vection). Displays were viewed with the head either stationary (passive radial flow) or laterally swaying to the beat of a metronome (active conditions). Multisensory conflict was imposed in active conditions by presenting displays that either: (i) compensated for head movement (active compensation condition), or (ii) presented pure radial flow with no compensation during head movement (active no compensation condition). In Experiment 1, impairing stereopsis by anisometropic suppression in healthy participants generated declines in reported vection strength, spatial presence and severity of cybersickness. In Experiment 2, vection and presence ratings were compared between participants with and without clinically-defined global stereopsis. Participants without global stereopsis generated impaired vection and presence similarly to those found in Experiment 1 by subjects with induced stereopsis impairment. We find that reducing global stereopsis can have benefits of reducing cybersickness, but has adverse effects on aspects of self-motion perception in HMD VR.

Evaluation of stereoacuity with a digital mobile application

Purpose Stereopsis is a fundamental skill in human vision and visual actions. There are many ways to test and quantify stereoacuity: traditional paper and new digital applications are both valid ways to test the stereoacuity. The aim of this study is to compare the results obtained using standard tests and the new Stereoacuity Test App developed by the University of Bergamo. Methods A group of 497 children (272 males), aged between 6 and 11 years old, were tested using different tests for the quantification of stereopsis at near. These tests were TNO, Weiss EKW, and the new developed Stereoacuity Test App. Results A one-way repeated measure ANOVA showed that the three tests give different thresholds of stereoacuity (p < 0.0001). Post hoc analyses with Bonferroni correction showed that all tests showed different thresholds (p < 0.0001). The lower threshold was obtained by Titmus Stereo Test followed by Stereoacuity App, Weiss MKW, and TNO. Conclusion The stereoacuity based on global stereopsis showed that the better values were obtained in order by Stereoacuity Test App, TNO, and Weiss EKW. However, the clinical significance of their values is similar. The new digital test showed a greater compliance by the child, showing itself in tune with the digital characteristics of today’s children.

A Flicker Therapy for the Treatment of Amblyopia

Background: Standard clinical treatment methods for amblyopia penalize the nonamblyopic eye, with subsequent compliance problems, and do not address the associated binocular vision abnormality. The purpose of this study is to evaluate a novel approach to amblyopia treatment that uses rapid alternating occlusion and flicker and aims to improve monocular and binocular vision. Methods: A pre-post (12 weeks) interventional study with historical data control. Children with anisometropic amblyopia (ages 5 to 17 years, n=23) were enrolled by consecutive sample. Subjects wore Eyetronix Flicker Glass, shutter glasses with liquid crystal lenses that rapidly alternated occlusion at a programmable frequency, for 1-2 hours daily while performing a near task of their choice, e.g., homework, computer. Outcome measures were: (1) bestcorrected LogMAR visual acuity (BCVA) and (2) Random Dot 2 stereopsis. Results: After 12 weeks of therapy, 96% (n=22) of the children treated improved BCVA in the amblyopic eye (p<0.001) - over 26% (n=6) improved 2 LogMAR lines or more (fellow eye BCVA did not change) - and 89% of the children with reliable data (n=18) improved global stereopsis. Conclusions: This relatively passive therapy has shown encouraging results as a potential treatment for amblyopia. The improvement in BCVA is comparable to previous studies that used traditional amblyopia therapies. The improvement in stereopsis suggests that the therapy promotes binocular vision. Notably, BCVA and stereopsis improved across all ages and in subjects who had previously plateaued with conventional therapies. Randomized masked and controlled studies are the next step to further quantify the clinical efficacy of this therapy.