Abstract
Continuous tracking provides a time-efficient paradigm for assessing the reflex behavior of human infants and children. We have used this approach to study the development of simultaneously measured vergence and accommodation responses, demonstrating robust almost adultlike responses to movement of a screen in depth by 3 months of age. In the context of atypical development, we have used computational simulation of optical defocus to understand its impact on the eye alignment and vergence responses of children in the critical period of binocular development. While matched defocus in the two eyes had only a mild effect on vergence tracking performance, unilateral defocus clearly disrupted the ability to continuously realign the eyes in response to small random changes in disparity, especially for the eye with the defocused image. These studies have important implications for the two age groups studied and for adults experiencing symptoms after presbyopia correction with monovision. The continuous tracking approach can be used in less than 2 minutes of testing to assess factors placing infants at risk for atypical development.