Motion-Acuity Test for Visual Field Acuity Measurement with Motion-Defined Shapes

Summary

A novel motion-based acuity test that allows the assessment of central and peripheral visual processing in low-vision and healthy individuals, along with goggles limiting peripheral vision compatible with MRI protocols, are described here. This method offers a comprehensive vision assessment for functional impairments and dysfunctions of the visual system.

Abstract

The standard visual acuity measurements rely on stationary stimuli, either letters (Snellen charts), vertical lines (vernier acuity) or grating charts, processed by those regions of the visual system most sensitive to the stationary stimulation, receiving visual input from the central part of the visual field. Here, an acuity measurement is proposed based on discrimination of simple shapes, that are defined by motion of the dots in the random dot kinematograms (RDK) processed by visual regions sensitive to motion stimulation and receiving input also from the peripheral visual field. In the motion-acuity test, participants are asked to distinguish between a circle and an ellipse, with matching surfaces, built from RDKs, and separated from the background RDK either by coherence, direction, or velocity of dots. The acuity measurement is based on ellipse detection, which with every correct response becomes more circular until reaching the acuity threshold. The motion-acuity test can be presented in negative contrast (black dots on white background) or in positive contrast (white dots on black background). The motion defined shapes are located centrally within 8 visual degrees and are surrounded by RDK background. To test the influence of visual peripheries on centrally measured acuity, a mechanical narrowing of the visual field to 10 degrees is proposed, using opaque goggles with centrally located holes. This easy and replicable narrowing system is suitable for MRI protocols, allowing further investigations of the functions of the peripheral visual input. Here, a simple measurement of shape and motion perception simultaneously is proposed. This straightforward test assesses vision impairments depending on the central and peripheral visual field inputs. The proposed motion-acuity test advances the capability of standard tests to reveal spare or even strengthened vision functions in patients with injured visual system, that until now remained undetected.

Introduction

Most of the available visual tests are directed to examine the features processed by central vision, relying on the input deriving from the central retina¹. The central retina has the densest cone-photoreceptor population for maximal visual acuity and lacks rod photoreceptors, which dominate the peripheral retina². The presence of densely packed photoreceptors is also reflected in an increased density of ganglion cells, which means a greater number of axons are directed to the optic nerve and, eventually, to the visual cortex. Outside the fovea towards the periphery, rods outnumber the cone photoreceptor

Protocol

All procedures were performed following the relevant guidelines and regulations and were approved by the Ethical Committee, WUM (KB/157/2017). Written consent was obtained from all participants, ensuring that they understood the general aim of the experiment and that they understood the inclusion of their data for statistical analysis purposes. All presented visual stimuli are generated using a Java-based desktop application (Viscacha2) created for the purpose of these experiments. 

1. Setup

1. Secure a quiet, dimmed room. Build a setup consisting of a computer, a keyboard, a flat display, an eye tracker (optional, depending o....

Results

The motion acuity task generates, for each participant, one result file for each stimuli procedure. An exemplary log file for a test participant has been included in the repository inside the doc folder. From row 1 to row 31, various settings are reported, such as the name of the patient and the configuration settings. The task block starts from row 34 and reports important information necessary for further analysis: event time, event type, trial, duration, selection, correct, success, experimenter, external stimuli, rev.......

Discussion

Here, a novel method is described for measuring visual motion acuity using a set of stimuli based on random dot kinematograms. The result is given as a minimal perceived difference between a circle and an ellipse, and it allows one to see when the subject stopped distinguishing shapes from each other. The smaller the difference achieved, the better acuity: it means that the subject can still detect where the circle is, even though it is almost identical to the ellipse. The motion-acuity test presented here brings the res.......

Materials

Name	Company	Catalog Number	Comments
Chinrest			custom-made
Computer			Windows 10 or higher
Display			1920 × 1080, 31 inches
EyeLink 1000 Plus	SR Research		desktop mount
USB Keyboard
USB mouse