Text-book of ophthalmology . 858 TEXT-BOOK OF OPHTHALMOLOGY This connection, however, is not one that is rigid and insusceptible of the contrary, we have the ability of emancipating ourselves from it within certainlimits—that is, while in the act of converging for a certain distance, of making a littlemore or a little less accommodation than corresponds to this distance. A man is madeto fix his gaze upon fine print at distance of 33 cm. Now, let us suppose that the sub-ject is emmetropic and thus has his far point (R) at infinity, while P is situated at 10 J* oo tOD W ID. L R Fio. 37
Text-book of ophthalmology . 858 TEXT-BOOK OF OPHTHALMOLOGY This connection, however, is not one that is rigid and insusceptible of the contrary, we have the ability of emancipating ourselves from it within certainlimits—that is, while in the act of converging for a certain distance, of making a littlemore or a little less accommodation than corresponds to this distance. A man is madeto fix his gaze upon fine print at distance of 33 cm. Now, let us suppose that the sub-ject is emmetropic and thus has his far point (R) at infinity, while P is situated at 10 J* oo tOD W ID. L R Fio. 376.—Schematic Representation of Relative Accommodation. cm., which corresponds to :i range of accommodation (A) of 10 D (Fig. 376). Of thisrange of accommodation 3 D (100-^33=3) will be employed if the subject is converg-ing for a distance of 33 cm. (=3 metre angles, sec; page 722). Now, a concave glass of1 D is placed before each eye. The subject will for the first moment have obscurationof vision, but will soon see distinctly. He has compensated for the diminution of therefractive power of this eye, caused by the — ID glass, by exerting 1 D more of his ac-commodation. But the convergence meanwhile remains unchanged—i. e., it is still ad-justed for 33 cm. The same phenomenon occurs when, instead of — 1 D, a glass of +1 D OPTICAL PROPERTIES OF THE NORMAL EYE 859 is placed before the eye. The refractive power of the eye is made too great by the con-vex glass, and this is neutralized by the eyes relaxing its accommodation through 1 this way we can bring stronger a
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