Accommodative and vergence responses to conflicting blur and disparity stimuli during development

Abstract

Accommodative and vergence responses of the typically developing visual system are generated using a combination of cues, including retinal blur and disparity. The developmental importance of blur and disparity cues in generating these motor responses was assessed by placing the two cues in conflict with each other. Cue-conflicts were induced by placing either -2 D lenses or 2 MA base-out prisms before both eyes of 140 subjects (2.0 months to 40.8 years) while they watched a cartoon movie binocularly at 80 cm. The frequency and amplitude of accommodation to lenses and vergence to prisms increased with age (both p < 0.001), with the vergence response (mean +/- 1 SEM = 1.38 +/- 0.05 MA) being slightly larger than the accommodative response (1.18 +/- 0.04 D) at all ages (p = 0.007). The amplitude of these responses decreased with an increase in conflict stimuli (1 to 3 D or MA) (both p < 0.01). The coupled vergence response to -2 D lenses (0.31 +/- 0.06 MA) and coupled accommodative response to 2 MA base-out prisms (0.21 +/- 0.02 D) were significantly smaller than (both p < 0.001) and poorly correlated with the open-loop vergence (r = 0.12; p = 0.44) and open-loop accommodation (r = -0.08; p = 0.69), respectively. The typically developing visual system compensates for transiently induced conflicts between blur and disparity stimuli, without exhibiting a strong preference for either cue. The accuracy of this compensation decreases with an increase in amplitude of cue-conflict.

Figure 1

Panel a: The experimental equipment. The core components are labeled. Panels b and c: A sample PowerRefractor (PR) image of a 4-month-old infant looking through a pair of −2 D lenses (panel b) and 2 MA base-out prisms (panel c).

Figure 2

Panel a: Mean (±1 SEM) response frequency of accommodation in LC and vergence in PC for all subjects within an age group. Panel b: Response proportion (i.e., ratio of the number of valid vergence responses in the PC condition to the total number of valid responses in the LC and PC conditions combined) of individual subjects plotted as a function of their age. Subjects with no valid response in both LC and PC conditions were not included in these analyses.

Figure 3

Representative raw traces of accommodation and vergence from a 3.8- and a 28-year-old in the LC condition (panel a) and PC condition (panel b). Raw traces from other age groups were similar to the traces shown here. The raw traces have been vertically shifted for clarity, with no shifting of the horizontal (time) axis. Downward on the ordinate indicates an increasing stimulus or response.

Figure 4

Raw traces from a 4.3-month-old and a 7.3-year-old illustrating dynamic interaction between accommodation and vergence in the PC condition of Experiment 1. The arrowheads illustrate apparent dynamic compensation for the convergence driven accommodation. The raw traces have been vertically shifted for clarity. The horizontal (time) relationship between the stimulus and response is maintained. Downward on the ordinate indicates an increasing stimulus or response.

Figure 5

Mean (±1 SEM) amplitude of the stimulated response (panel a) and the coupled response (panel b) in the LC and PC conditions of Experiment 1. Only subjects with at least one stimulated response (i.e., response frequency >0%) were included and the mean for each subject only includes their responses that met the inclusion criteria.

Figure 6

Panel a: Mean (±1 SEM) amplitudes of the stimulated accommodative response and coupled vergence response in the LC condition of Experiment 1 and in DOL condition of Experiment 2. Panel b: Mean (±1 SEM) amplitudes of stimulated vergence response and coupled accommodative response in the PC condition of Experiment 1 and in BOL condition of Experiment 2.

Figure 7

Mean (±1 SEM) response frequency of stimulated responses and amplitudes of the stimulated and coupled responses in the LC (panel a) and PC (panel b) conditions for three different conflict amplitudes.

Figure 8

Panel a: Cycloplegic spherical equivalent refraction (SER) plotted as a function of subject’s age. SER from right and left eyes were averaged. Panel b: Response proportion of individual subjects plotted as a function of their cycloplegic SER. Panel c: The response amplitude of accommodation plotted as a function of the cycloplegic SER in the LC condition. Panel d: The response amplitude of vergence plotted as a function of the cycloplegic SER in the PC condition.