In The Marriage of Heaven and Hell, William Blake says that “If the doors of perception were cleansed everything would appear to man as it is: infinite.” In vision, of course, there is a simple connection between optical infinity and perceived visual clarity, at least for distance vision in emmetropes. Contact lens practitioners and refractive surgeons have taken things one step further. By exploiting the brain’s ability to perceptually suppress central vision in one eye when the two eyes are receiving disparate stimuli, they have found that it is often possible to correct presbyopic ametropes using a distance correction for the dominant eye, and a near correction for the non-dominant eye. In this “monovision” situation, patients thus have to suppress the central vision in their non-dominant eye for distance tasks, and in their dominant eye for near tasks.

In essence, monovision is a form of deliberately introduced anisometropia, and it is this property that John Phillips has exploited in a highly original study, in this issue of BJO (p 1196), that provides new insight into the role of blur in regulating eye growth and refractive development in children. In this small clinical trial, children received a full myopic correction for their dominant eye and an undercorrection of up to +2.00 D for their non-dominant eye (as discussed below, the undercorrection led to the vision in the children’s non-dominant eyes being continually blurred). The results were striking: the rate of myopia progression in the undercorrected eye was found to be approximately 50% of that in the fully corrected eye. Furthermore, the reduced rate of myopic progression was attributed to a reduced rate of vitreous chamber elongation, consistent with a slowing of the primary structural change responsible for causing …