Cues for the control of ocular accommodation and vergence during postnatal human development

Abstract

Accommodation and vergence help maintain single and focused visual experience while an object moves in depth. The relative importance of retinal blur and disparity, the primary sensory cues to accommodation and vergence, is largely unknown during development; a period when growth of the eye and head necessitate continual recalibration of egocentric space. Here we measured the developmental importance of retinal disparity in 192 typically developing subjects (1.9 months to 46 years). Subjects viewed high-contrast cartoon targets with naturalistic spatial frequency spectra while their accommodation and vergence responses were measured from both eyes using a PowerRefractor. Accommodative gain was reduced during monocular viewing relative to full binocular viewing, even though the fixating eye generated comparable tracking eye movements in the two conditions. This result was consistent across three forms of monocular occlusion. The accommodative gain was lowest in infants and only reached adult levels by 7 to 10 years of age. As expected, the gain of vergence was also reduced in monocular conditions. When 4- to 6-year-old children read 20/40-sized letters, their monocular accommodative gain reached adult-like levels. In summary, binocular viewing appears necessary under naturalistic viewing conditions to generate full accommodation and vergence responses in typically developing humans.

The Effect of Lens-Induced Anisometropia on Accommodation and Vergence during Human Visual Development

“…3). The responses in each epoch were included in the analyses only if they met all the criteria described here 32 :…”

“…Third, the subject generated an eye movement to track the stimulus; therefore, the accommodation and vergence responses represented a valid attempt to follow the target along the midline between the eyes. 32 This criterion was applied to the data from the left eye in all viewing conditions, irrespective of the viewing condition for the right eye. All response epochs with a correlation of Ն0.7 between left eye position and stimulus position were automatically included in the analyses.…”

“…The defocus and gaze position calibration procedures have been described in detail previously. 32,41,46 Briefly, the defocus calibration factor was determined by placing trial lenses (ϩ1 D to ϩ4 D in steps of 1D) in front of the right eye, which was occluded using an IR filter, while the unoccluded left eye of the subject fixated on a target placed at 50 cm. Similarly, the gaze position calibration function was determined by optically shifting the Purkinje image of the occluded eye using base-out prisms (4 pd to 16 pd in steps of 4 pd) placed in front of the filter while the subject continued to fixate at 50 cm.…”

“…The slopes of the functions were determined using linear regression, and these slopes were used to scale each participant's raw data. 32,43,47 The default PR calibration was used for subjects who did not complete that part of the data collection. Calibration slopes of individual subjects are approximately evenly distributed about the default PR calibration slope values, 46 with no strong age-related trends.…”

“…Calibration slopes of individual subjects are approximately evenly distributed about the default PR calibration slope values, 46 with no strong age-related trends. 32,46 It was, therefore, assumed that the errors introduced by using the default PR calibration summed to zero in the calculation of mean population responses.…”