In order to understand how refractive error can cause squint, one must first understand how the act of accommodation is linked to the act of convergence. That is to say, we must realise that when we focus upon an object, not only is each individual eye separately focused on it, but the eyes swivel together by the requisite amount to allow them both to view the object at once. A given amount of accommodation must, therefore, be associated with an equivalent amount of convergence. In hypermetropic subjects this relationship is disturbed. In order to overcome hypermetropia, the eyes must accommodate and sometimes this excessive focusing induces an excess of convergence, hence causing a squint. This type of accommodative squint can be fully corrected by wearing spectacles: when the glasses are on, the eyes are straight; and when they are off, one eye turns in. More often, the squint is only partially accommodative and is improved, but not eliminated, by wearing glasses. The convergent squint associated with hypermetropia is the commonest type of childhood squint.
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