Cues For Accommodation and Vergence in Infancy and Early Childhood.

PURPOSE: Focused binocular fixation on a target relies on a combination of accommodation and vergence oculomotor responses. These require recalibration during early development, as a result of changes in refractive error and increases in inter-pupillary distance (IPD). This study tracked the roles of blur and disparity cues in these motor responses during this period.

METHODS: 103 infants were followed from 3 months until 3 years of age. Their accommodation and vergence responses to a movie with naturalistic spatial amplitude spectra were recorded simultaneously using eccentric photorefraction and Purkinje image tracking (PowerRefractor, MCS). The target was moved repeatedly between 90 and 33cm and recordings were made in i) full cue binocular conditions (Bn), ii) the absence of disparity cues while occluding one eye with an IR filter (Oc), and iii) a reduced blur cue condition (Bl) (the image was covered with a lowpass spatial filter and masked with a Difference of Gaussian).

RESULTS: Changes in vergence and accommodation between the two viewing distances were computed for each condition. The ratio of vergence to accommodation was compared across the three conditions. Relative to the full cue Bn baseline, the ratio in the absence of disparity (Oc) was reduced at all ages (F = 0.22, p=0.80), suggesting that accommodative convergence is consistently low in early childhood. In contrast, the ratio in the Bl condition was lower in infancy and childhood than in adults (F=4.78, p=0.02), suggesting convergence accommodation is higher during early development.

CONCLUSIONS: The results suggest that vergence driven by cues other than disparity remains low in early childhood, while accommodation driven by cues other than blur is increased. This relationship is theoretically beneficial during the developmental period when accommodative demand is typically high due to hyperopia and vergence demand is low due to the narrow IPD. Meeting abstract presented at VSS 2015.