284 
NEAR AND DISTANT SIGHT. 
less than half an hour) could not be made to meet in 
less than three inches and a quarter ; and, on the following 
day, the pupil being more dilated, the lines did not meet till 
they were at the distance of nearly four inches. In a third 
instance, viz. that of a lady of forty-five years of age, who 
had been remarkably near-sighted from her infancy, and for 
many years had used concave glasses of the fifteenth number 
(which number is ground on each side upon a tool, the radius 
of which is only three inches) the sight was become so con- 
fused in both eyes, that she saw nothing distinctly, and was 
unable to read letters of the size that are used in the printed 
Transactions of the Royal Society, either with or without a 
glass. In this case, after the pupils had been dilated by the 
application of the belladonna, the sight was so much improved, 
that she was able to read a print of the above-mentioned size, 
at the distance of two inches with either eye. I do not 
insist, however, on the present case, because, though there 
was not any visible opacity in the crystalline, this sometimes 
exists, in a small degree, without being perceptible even to an 
attentive observer ; and it may be doubted whether the amend- 
ment in the lady’s vision were not occasioned solely by tho 
_ retraction of the iris from before a part of the crystalline that 
was not yet become opaque j it being well known, that the 
outer part of this lens not unfiequently retains its transparency 
for some time after an opacity has commenced in the part that 
surrounds its centre. 
It is evident, that near-sightedness has no dependence on the 
greater or smaller degree of convexity possessed by the cornea, 
when this circumstance is considered alone j since the length 
of the axis of the eye, from the cornea to the retina, and the 
greater or smaller degree of convexity in the crystalline hu- 
mour, must be also regarded, before the distance of accurate 
vision can be determined. 
It is no less evident, that near-sightedness is not necessarily 
occasioned by a morbid protrusion of the whole eye; since 
some persons are born with eyes of this description, and otheri 
acquire the peculiarity, when further advanced in life, in con- 
sequenc* 
