A Form of Hypermetropia 215
rable. It is not caused by hardening of the lens, but by a strain to see at the near-point. It has no necessary con nection with age, since it occurs, in some cases, as early as ten years, while in others it never occurs at all, al though the subject may live far into the so-called pres byopic age. It is true that the lens does harden with ad vancing years, just as the bones harden and the struc ture of the skin changes; but since the lens is not a factor in accommodation, this fact is immaterial, and while in some cases the lens may become flatter, or lose some of its refractive power with advancing years, it has been observed to remain perfectly clear and unchanged in shape up to the age of ninety. Since the ciliary muscle is also not a factor in accommodation, its weakness or atrophy can contribute nothing to the decline of accom modative power. Presbyopia is, in fact, simply a form of hypermetropia in which the vision for the near-point is chiefly affected, although the vision for the distance, contrary to what is generally believed, is always lowered also. The difference between the two conditions is not always clear. A person with hypermetropia may or may not read fine print, and a person at the presbyopic age may read it without apparent inconvenience and yet have imperfect sight for the distance. In both conditions the sight at both points is lowered, although the patient may not be aware of it.
It has been shown that when the eyes strain to see at the near-point the focus is always pushed farther away than it was before, in one or all meridians; and by means of simultaneous retinoscopy it can always be demon strated that when a person with presbyopia tries to read fine print and fails, the focus is always pushed farther away than it was before the attempt was made, indicat-