Functional relationship between myopia, accommodative stress and against-the-rule astigmia: a hypothesis.

A model is proposed to explain the well-established tendency for against-the-rule astigmatism to precede and be predictive of the later development of myopia. It is hypothesized that the against-the-rule astigmatism is a functional adaptation to reduce near point stress by permitting reduced accommodative output (increased lag of accommodation) while maintaining resolution for the primarily vertically-oriented characters of the English language.