Development of refraction and strabismus

In the past year a number of studies have provided insights into the mechanisms whereby the eye can maintain coordinated growth to achieve emmetropia. Research into factors that may lead to a failure to emmetropize also has been promising. The effect of early spectacle intervention has been debated, with some evidence from animal studies suggesting that lenses may interfere with emmetropization. Human data on this topic are limited but do not appear to show the deleterious effects of lenses reported in the animal studies. The role of early astigmatism in the emmetropization process is not clear. Myopia research continues to hold promise for the eventual discovery of treatments to slow progression. With respect to the development of strabismus, there are many mechanisms for its induction. The problem is to identify the primary ones and their interactions. This article reviews some of the newer candidates, including pulleys that affect extraocular-muscle action and the role of nasally biased monocular optokinetic nystagmus. An understanding of the critical periods of the various visual dimensions involved in the development of strabismus is also crucial.