This article, Egocentric Distance Perception Disorder in Amblyopia, is intriguing from a variety of angles, not the least of which is its origin of publication in Psychologica Belgica – the journal of the Belgian Association for Psychological Science. After describing amblyopia as a neurological disorder in the visual cortex due to a mismatch between the two eyes, the authors cite evidence that quality of life is significantly reduced for individuals with amblyopia. This includes not only a propensity toward the visual factors of blur, diplopia, decline in distance judgement, and other functional disorders, but also psychological distress, such as lack of self-confidence, depression, and family tension.
The authors explain that egocentric distance perception is a psychological process in which observers use various depth cues to estimate the distance between the target and themselves that plays an important role in quality of life. Approximately 40% of the items tested on the main quality of life scales such as the Amblyopia and Strabismus Questionnaire (ASQE); the 20-item Adult Strabismus questionnaire (AS-20); and the Amblyopia Treatment Index (ATI) are related to egocentric distance perception including estimating distance, going down stairs, or parking a car.
A graphic is produced to depict three regions of visual space that can be differentially affected in amblyopia: personal space (there is a typo in the graphic), action space, and vista space. Pesonal space or egocentric distance within a meter or two is heavily influenced by accommodation, convergence, and motion. Beyond that, and out to about 30 meters is action space which is heavily influenced by visual angle and binocular disparity. And beyond that is vista space heavily laden with the cues of aerial perspective and relative size.
All this sounds remarkably similar to the partitioning of visual space consistent with Rourke’s neuropsychology of personal, peripersonal, and extrapersonal space, and embodied cognition as we have discussed relative to Brock’s String and Sanet’s Space Fixator (see here). It also reinforces the importance of emphasizing binocular tasks in amblyopia, rather than getting hung up on monocular visual acuity as the be-all and end-all of impairment or success. In particular, stereopsis and stereo-motion play an important role in real world visuomotor tasks such as walking, grasping objects, and driving, as noted in the review paper they cite by Grant and Moseley. A type of dyskinesis occurs in amblyopia in which motor planning and execution in impaired particularly when tasks are novel or speed-related.
Another interesting study reviewed in this article is by Ooi and He on Space Perception of Strabismic Observers in the Real World Environment. Looking at their research paradigm, one is reminded of principles inherent in Space Fixator and Marsden Ball procedures, in contrasting monocular to binocular performance, and in guiding visual judgment through lenses, prisms, and movement in 3D space. As Ooi and He write: “Poor stereopsis as a result of childhood disorders of strabismus and/or amblyopia persists into adulthood, and affects everyday perception and actions in the near and intermediate visual space. It is notable that at the time of testing none of our observers would be classified as amblyopic when referenced to the American Academy of Ophthalmology’s guideline for visual acuity deficit.”