Tonic accommodation predicts closed-loop accommodation responses

Abstract

The purpose of this study is to examine the potential relationship between tonic accommodation (TA), near work induced TA-adaptation and the steady state closed-loop accommodation response (AR). Forty-two graduate students participated in the study. Various aspects of their accommodation system were objectively measured using an open-field infrared auto-refractor (Grand Seiko WAM-5500). Tonic accommodation was assessed in a completely dark environment. The association between TA and closed-loop AR was assessed using linear regression correlations and t-test comparisons. Initial mean baseline TA was 1.84diopter (D) (SD±1.29D) with a wide distribution range (-0.43D to 5.14D). For monocular visual tasks, baseline TA was significantly correlated with the closed-loop AR. The slope of the best fit line indicated that closed-loop AR varied by approximately 0.3D for every 1D change in TA. This ratio was consistent across a variety of viewing distances and different near work tasks, including both static targets and continuous reading. Binocular reading conditions weakened the correlation between baseline TA and AR, although results remained statistically significant. The 10min near reading task with a 3D demand did not reveal significant near work induced TA-adaptation for either monocular or binocular conditions. Consistently, the TA-adaptation did not show any correlation with AR during reading. This study found a strong association between open-loop TA and closed-loop AR across a variety of viewing distances and different near work tasks. Difference between the correlations under monocular and binocular reading condition suggests a potential role for vergence compensation during binocular closed-loop AR.

Keywords: Accommodation response; TA-adaptation; Tonic accommodation; Vergence.

Fig. 1

Schematic representation of experimental task sequence.

Figure 2

Frequency distribution of baseline tonic accommodation (TA1).

Figure 3

Scatterplot of the effect of TA1 on accommodation responses while viewing static targets at different viewing distances. Linear regression lines are plotted as dotted lines; the target’s accommodative stimulus demand is plotted as a solid, horizontal line.

Figure 4

Scatterplot of the effect of TA1 on the accommodation response while viewing: (A) a monocular 3D static target and (B) continuous monocular reading at 3D. The effect of Baseline TA2 on the accommodation response while performing continuous binocular reading at 3D is shown in Figure 4C. Linear regression lines are plotted as dotted lines; the target is plotted as a solid, horizontal line.

Figure 5

Frequency distribution of near work-induced TA adaptation: (A) monocular reading task, (B) binocular reading task.