. Good and bad eyesight : and the exercise and preservation of vision. es,shown diagrammatically at I, i, in Fig. 34, than uponany others; since these are chiefly concerned in thefunction of convergence, by which the eyes are rolledinwards, and are thus moved, at will, from the positionnearly of parallelism, which they assume when lookingat an infinitely distant object, to that which they assumewhen directed to some nearer point. If we bring anobject of vision slowly near to the eyes of another per-son, who looks at it as it approaches, we may watchthe movement of convergence ; and we shall se
. Good and bad eyesight : and the exercise and preservation of vision. es,shown diagrammatically at I, i, in Fig. 34, than uponany others; since these are chiefly concerned in thefunction of convergence, by which the eyes are rolledinwards, and are thus moved, at will, from the positionnearly of parallelism, which they assume when lookingat an infinitely distant object, to that which they assumewhen directed to some nearer point. If we bring anobject of vision slowly near to the eyes of another per-son, who looks at it as it approaches, we may watchthe movement of convergence ; and we shall see that, CONVERGENCE. 95 when the effort to look at the near object ceases, theeyes are rolled back to the position of repose, nearly inthe middle of each eyelid opening. This rolling back isdone by the external straight muscles, e, e, Fig. 34, assoon as the action of the internal muscles is suspended,and any continuance of forced or extreme convergencesoon becomes excessively fatiguing. For a short time,however, the eyes may be rolled inwards in a very con- FlG.
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Keywords: ., bookcentury1800, booksubj, booksubjecteye, booksubjecteyediseases
