350 W. LeConte Stevens—Physiological Optics. 
3. ReLation oF AxtaL ADJUSTMENT TO FocaL ACCOMMODATION. 
The focal and axial adjustments of the eyes biel necessarily 
dissociated to some extent, if clear vision is had with the stereo- 
measurements has been made with the Bokiatarioe ‘of Dr. J. H. 
Shorter, of the New York Eye and Ear Infirmary. In the pre- 
liminary examination it was found that at the distance of 9™ it 
was possible to read Snellen’s test-type intended for’ average 
vision at 6". By the usual formula, therefore, my acuity of 
vision is 2. With visual lines approximately. narallet: there 
is hyperopia to an extent not exceeding one dioptric.* This is 
capable of correction, therefore, with a bi-convex lens whose 
focal length is 1”. But when the visual lines are diverged 5°, 
latent hyperopia to the extent of nearly one dioptric more is 
revealed by the use of appropriate test- lenses, while the near- 
point of distinct vision is found, by means of test-type, to 
have receded proportionally. This fact could not well have 
been ascertained otherwise, except by the use of pap ease with 
its well known disagreeable consequences. ‘I'he experiment 
shows that, in the present case at least, full relaxation of the 
ciliary muscles is not ee by making the visual lines 
parallel. For emmetropic eyes it is usually range that 
negative accommodation advanced by Von Graefe+ and se 
has not been generally accepted. 
In experimenting upon range of accommodation I employed 
a pair of narrow cards on which were vertically printed similar 
specimens of test-type, intended to be read with average acuity 
of vision at the distance of 67™. On a large sheet of paper, 
covering a table, a median line was drawn, terminating at the 
edge in front of the mid-point between the eyes. Making due 
allowance for the distance of these from the edge, pairs of lines 
were drawn, along which the visual lines could be directed at 
will. Upon them the cards were placed so that binocular fusion 
of images could be secured for fixed values of the optic angle, 
to which the directions of the lines had been adapted. long 
these the cards were made to recede and approach until the 
farthest and nearest points were found at which distinct binocu- 
lar vision was possible, myself being kept ignorant of the record 
taken until the whole series of measurements had been completed. 
or dioptric system of seaprein the refraction of the eye, see Carter on 
styedent pp. 43-47; Macmillan, 
+ Soelburg Wells, Diseases of the Tye: Appleton, 1881. 
