The use of cues to convergence and accommodation in naïve, uninstructed participants

Abstract

A remote haploscopic video refractor was used to assess vergence and accommodation responses in a group of 32 emmetropic, orthophoric, symptom free, young adults naïve to vision experiments in a minimally instructed setting. Picture targets were presented at four positions between 2 m and 33 cm. Blur, disparity and looming cues were presented in combination or separately to asses their contributions to the total near response in a within-subjects design. Response gain for both vergence and accommodation reduced markedly whenever disparity was excluded, with much smaller effects when blur and proximity were excluded. Despite the clinical homogeneity of the participant group there were also some individual differences.

Figure 1

The Remote Haploscopic Videorefractor. A. Motorised beam. B. Target monitor. C. Upper concave mirror. D. Lower concave mirror. E. Hot mirror. F. Image of participant’s eye where occlusion takes place. G. PlusoptiX SO4 PowerRef II. H. Headrest J. Raisable black cloth screen.

Figure 2

a) & b) Clown target alternating at 1Hz containing bright colours, high contrast and range of spatial frequencies. Black outlines to picture elements do not reproduce well in this reduced illustration c) Difference of Gaussian patch. Colour alternated between green and yellow with equal luminance at 1Hz.

Figure 3

RHP vs dynamic retinoscopy of 59 participants fixating targets at 33cm, 50cm,1m and 2m. Error bars indicate 95%CI.

Figure 4

Example of vignette identification. Plots of partially processed data (before degrees converted to metre angles and angle lambda corrected) used for vignette identification. Responses against time (x-axis) to identify target position and continuous data sections. y-axis scale in dioptres for accommodation and degrees for vergence. Vignettes of 25 continuous data points were selected (shaded) to represent a sample of stable response at each fixation distance

Figure 5

Sample of actual accommodation data over a blink. Dark shaded area = missing points during blink which fulfil spike identification criterion. Paler shaded area = removed points during blink recovery. Points either side of excluded portion averaged and substituted.

Figure 6

Example of a typical response plot after correction for accommodation calibration, angle lambda and IPD. Vergence plotted in metre angles (MA). Uniocular gaze positions summed to show binocular vergence. Uniocular accommodation averaged.

Figure 7

Response to demand in each stimulus condition. Solid points = vergence, open points = accommodation, dotted line = ideal response to demand. Error bars represent 95%CI.

Figure 8

Vergence and accommodation intercepts. “bdp” = all cues present, “dp(−b)” = disparity and proximity present, blur removed, “b” = blur only etc.

Figure 9

Examples of different individual response types. Grey bars represent vergence slope, striped bars represent accommodation slope. Letters on y-axis represent cue available (or excluded) e.g. dp(−b) = disparity & proximity present, blur removed. a) typical response in which the vergence and accommodation responses are both reduced when the disparity cue is absent, b) good responses for most stimuli, c) accommodation lag d) disrupted by any cue removal, e) accommodation lead as well as differential response to specific cue removal . Categories are not mutually exclusive.

Figure 10

AC/A and CA/C relationship between groups in Figure 9 (±SE). Accommodative vergence represented by gain of vergence response in the “blur only” condition. Vergence accommodation represented by gain of accommodation response in “disparity only” condition. Accommodative vergence gain not significantly different between groups. Vergence accommodation significantly lower in the “lag” group (asterisked). .