The development of binocular function in infancy

Development of Relative Disparity Sensitivity in Human Visual Cortex

Stereopsis is the primary cue underlying our ability to make fine depth judgments. In adults, depth discriminations are supported largely by relative rather than absolute binocular disparity, and depth is perceived primarily for horizontal rather than vertical disparities. Although human infants begin to exhibit disparity-specific responses between 3 and 5 months of age, it is not known how relative disparity mechanisms develop. Here we show that the specialization for relative disparity is highly immature in 4- to 6-month-old infants but is adult-like in 4- to 7-year-old children. Disparity-tuning functions for horizontal and vertical disparities were measured using the visual evoked potential. Infant relative disparity thresholds, unlike those of adults, were equal for vertical and horizontal disparities. Their horizontal disparity thresholds were a factor of ∼10 higher than adults, but their vertical disparity thresholds differed by a factor of only ∼4. Horizontal relative disparity thresholds for 4- to 7-year-old children were comparable with those of adults at ∼0.5 arcmin. To test whether infant immaturity was due to spatial limitations or insensitivity to interocular correlation, highly suprathreshold horizontal and vertical disparities were presented in alternate regions of the display, and the interocular correlation of the interdigitated regions was varied from 0% to 100%. This manipulation regulated the availability of coarse-scale relative disparity cues. Adult and infant responses both increased with increasing interocular correlation by similar magnitudes, but adult responses increased much more for horizontal disparities, further evidence for qualitatively immature stereopsis based on relative disparity at 4-6 months of age.SIGNIFICANCE STATEMENT Stereopsis, our ability to sense depth from horizontal image disparity, is among the finest spatial discriminations made by the primate visual system. Fine stereoscopic depth discriminations depend critically on comparisons of disparity relationships in the image that are supported by relative disparity cues rather than the estimation of single, absolute disparities. Very young human and macaque infants are sensitive to absolute disparity, but no previous study has specifically studied the development of relative disparity sensitivity, a hallmark feature of adult stereopsis. Here, using high-density EEG recordings, we show that 4- to 6-month-old infants display both quantitative and qualitative response immaturities for relative disparity information. Relative disparity responses are adult-like no later than 4-7 years of age.

Convergence and Accommodation Development Is Preprogrammed in Premature Infants

PURPOSE

This study investigated whether vergence and accommodation development in preterm infants is preprogrammed or is driven by experience.

METHODS

Thirty-two healthy infants, born at mean 34 weeks gestation (range, 31.2-36 weeks), were compared with 45 healthy full-term infants (mean 40.0 weeks) over a 6-month period, starting at 4 to 6 weeks postnatally. Simultaneous accommodation and convergence to a detailed target were measured using a Plusoptix PowerRefII infrared photorefractor as a target moved between 0.33 and 2 m. Stimulus/response gains and responses at 0.33 and 2 m were compared by both corrected (gestational) age and chronological (postnatal) age.

RESULTS

When compared by their corrected age, preterm and full-term infants showed few significant differences in vergence and accommodation responses after 6 to 7 weeks of age. However, when compared by chronological age, preterm infants' responses were more variable, with significantly reduced vergence gains, reduced vergence response at 0.33 m, reduced accommodation gain, and increased accommodation at 2 m compared to full-term infants between 8 and 13 weeks after birth.

CONCLUSIONS

When matched by corrected age, vergence and accommodation in preterm infants show few differences from full-term infants' responses. Maturation appears preprogrammed and is not advanced by visual experience. Longer periods of immature visual responses might leave preterm infants more at risk of development of oculomotor deficits such as strabismus.

Quantifying the ontogeny of optokinetic and vestibuloocular behaviors in zebrafish, medaka, and goldfish

We quantitatively studied the ontogeny of oculomotor behavior in larval fish as a foundation for studies linking oculomotor structure and function with genetics. Horizontal optokinetic and vestibuloocular reflexes (OKR and VOR, respectively) were measured in three different species (goldfish, zebrafish, and medaka) during the first month after hatching. For all sizes of medaka, and most zebrafish, Bode plots of OKR (0.065-3.0 Hz, +/-10 degrees/s) revealed that eye velocity closely followed stimulus velocity (gain > 0.8) at low frequency but dropped sharply above 1 Hz (gain < 0.3 at 3 Hz). Goldfish showed increased gain proportional to size across frequencies. Linearity testing with steps and sinusoids showed excellent visual performance (gain > 0.8) in medaka almost from hatching; but zebrafish and goldfish exhibited progressive improvement, with only the largest equaling medaka performance. Monocular visual stimulation in zebrafish and goldfish produced gains of 0.5 versus <0.1 for the eye viewing a moving versus stationary stimulus pattern but 0.25 versus <0.1 in medaka. Angular VOR appeared much later than OKR, initially at only high accelerations (>200 degrees /s at 0.5 Hz), first in medaka followed by larger (8.11 mm) zebrafish; but it was virtually nonexistent in goldfish. Velocity storage was not observed except for an eye velocity build-up in the largest medaka. In summary, a robust OKR was achieved shortly after hatching in all three species. In contrast, larval fish seem to be unique among vertebrates tested in their lack of significant angular VOR at stages where active movement is required for feeding and survival.

On infantile esotropia with nystagmus in abduction

Infantile esotropia with nystagmus in abduction is characterized by early onset, jerk nystagmus in abduction, and dissociated vertical deviation, among other features. Electro-oculographic tracings present easily recognizable patterns both in saccadic and pursuit movements. Visual evoked responses are asymmetric in most cases and optokinetic nystagmus is invariably asymmetric. Visual cortex maldevelopment seems to play a major pathogenic role. Recent findings in myelomeningocele and in patients with posterior fossa tumors suggest that pathological alterations in this area may tend to induce similar anomalies in electro-oculographic and optokinetic nystagmus recordings. Posterior fossa damage or impairment is therefore suspected to be a possible causative factor in the development of infantile esotropia with nystagmus in abduction.