Change of Perceived Size of Object by Convergence or Divergence without Accommodation Measured by Three-Dimensional Scenography

Abstract

Purpose : In humans, a function that adapts the perceived size of object depending on the perceived distance is thought to exist, but the detailed mechanism is unclear. Convergence micropsia (a target subtending a constant visual angle looks smaller when the eyes are converged than when in primary position) is reported in intermittent exotropia. Structural details of convergence micropsia are unclear. The effects of exotropia or esotropia on perceived size remain unknown.
We designed a method to study the change in perceived size depending on vergence. Using 3D scenography, the perceived sizes of a fixation target in different binocular parallaxes produced by varying the angle of vergence (both convergence and divergence) without accommodation were measured. The relationship between perceived size and convergence was evaluated by determining how a convergence load affects the relationship.

Methods : Twenty healthy subjects aged 28 ± 8 (mean ± standard deviation) years were studied. Two identical targets were projected on a screen 4 m ahead using a VPL-VW90ES video projector (Sony), which were viewed stereoscopically with 3D glasses (TDG-BR100, Sony). The target had a diameter of 23.7 cm on the screen, and angular size of 3.4°. For the left target (A), different binocular parallaxes could be produced by horizontal shifting in opposite direction. The size of the right target (B) could be varied. Target A was presented in different binocular parallaxes with angles of vergence varying randomly from −2.0° (divergence) to 4.0° (convergence) in steps of 0.5°. The perceived sizes of target A and target B were compared. The size of target B was adjusted in steps of 1% until the perceived size completely matched that of target A. The slope of the regression line for vergence angle versus percent change in perceived size was obtained from all data. The same procedure was performed with a convergence load of 4 PD exerted on the ophthalmoscope frames.

Results : The slope of this model was −5.8%/degree angle [determination coefficient (R²)=0.67, p<0.001]. The slope of the model with the convergence load was −5.4%/degree angle (R²=0.66, p<0.001).

Conclusions : The perceived size of the same retinal image becomes smaller with increased convergence. The slope for each subject was constant, indicating that exodeviation or esodeviation to achieve binocular vision may affect the perceived size.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.