My Project

Vision screening is well over a century old yet its efficacy remains unclear. Originally, screening targeted school-aged children, however, over time screening has shifted to pre-school children. This shift reflects the fact that in the western world at least, the most common vision problems in infants and children are those of strabismus (turned eye) and amblyopia (lazy eye). Large refractive errors of a number of forms, hyperopia (farsightedness), astigmatism (unequal focus within the eye) and anisometropia (unequal focus between the two eyes) can serve as precursors to strabismus and /or amblyopia. In theory, vision screening is a supportable activity in that the conditions are significant (3 to 5% of the population) and treatment is readily available in primary eye care for refractive errors and amblyopia. Pre-school vision screening in western countries is often conducted using subjective tests of visual acuity (which detects refractive errors and amblyopia) and stereo-acuity (which checks for strabismus). Researchers have shown however, that visual acuity has limitations in vision screening pre-school children. Its sensitivity (ability to detect a problem vs. missing it) is low and not readily corrected by varying the cut-off levels. In addition, pre-school children show an age effect in their performance where the younger child is more likely to be over-referred. In the current climate of fiscal conservatism, such findings can allow governments to withdraw vision screening on the basis that it is not effective. What are needed are better methods that directly and objectively test for refractive errors and strabismus and thereby detect the precursors to amblyopia. The objectives of this research program are to develop instrument designs that will provide accurate measures of hyperopia in children and to measure the validity of a pre-school screening program using objective instrumentation. We have now extended the project to study the potential links between hyperopia and emergent literacy development in children. In addition to the vision tests we are testing knowledge of conventions of print and spelling, word recognition, phonological awareness and receptive vocabulary, as well as examining the literacy experiences of children. Data collected over two years has shown that hyperopic children lag behind emmetropic children in some of these tests, after controlling for other factors that affect emergent literacy skills in children, and ruling out developmental concerns. We have also shown that the lag occurs in spite of no noticeable difference in visual cognitive skills between hyperopes and emmetropes.