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It has long been known that hyperopes easily become the victims of exaggerated strabismus constituting squint; the disturbance between the two functions— accommodation and convergence—leading to this result. The accommodation is measured and recorded by the Nagels plan of metric angles—a plan which corresponds with the metric measurement of the accommodation.
An emmetrope looking at an object half a meter away would use two diopters of accommodation; he would at the same time converge to the same point, and thus convergence would be expressed by two meter angles, so that we record it thus: A = 2 D; C = 2 m a. If the object looked at be 20 cm. off, then: A = 5 D; C = 5 m a. The position of the p. p. (near point) and the p. r. (far point) of accommodation vary according as the patient is emmetropic, hyperopic or myopic; and in all, the p. p.
MEANY WB. A FEW NOTES ON SQUINT.. JAMA. 1897;XXVIII(22):1017–1019. doi:10.1001/jama.1897.02440220013002f