THe MIcROscOoPE. 29 
ASTIGMATISM PRACTICALLY CONSIDERED IN 
MICROSCOPIC WORK. 
BY JAMES K. STOCKWELL M. D. OSWEGO N. Y. 
N article in Tur Microscope of January, 1886, on “Astigma- 
tism and its Relation to the Use of Optical Instruments,” 
by Ernest Gundlach, was a remarkably clear and concise treat- 
ment of a common and annoying defect of the human eyes, and 
interested me greatly, as it undoubtedly did very many others 
of the numerous readers of that valuable journal. 
It occurs to me that the subject of asymmetry of the human 
eye has been very lightly if at all touched upon by any of the 
various writers on optical matters, outside of authors of text- 
books on defects of vision and the use of spectacles. 
Mr. Gundlach says, and very truly, that “Astigmatism is 
very common, and even the healthy eye is not entirely free 
from it.” It is so common and so little understood that many 
people, even professional and other educated persons, who 
should be somewhat familiar with the common laws of optics, 
go through the world without knowing that certain lines are less 
clearly defined to their eyes than they should be, and there are 
other lines having different direction only, being otherwise 
similar. And if, perchance, they are conversant with the fact, 
remain wholly at a loss how to account for it, and so perhaps in 
time come to believe that their eyes are really no different 
from other and more nearly perfect eyes—emmetropic eyes, or 
those which in a state of rest (without any effort of the accom- 
modation) bring parallel rays of light,in all meridians, to a 
focus on the layer of rods and cones of the retina and there form 
a clear and distinct inverted image of the point, line or object 
from which they come. 
Astigmatism requiring a concave or convex cylindrical lens 
of more than one hundred or even seventy-two inches focal 
length for proper correction is usually too slight and unnotice- 
able to demand attention unless complicated by long or short 
sight; occasionally, however, even that slight degree of asym- 
metry gives rise to much discomfort, if to no other trouble, dur- 
ing prolonged and close use of the eyes. 
Mr. Gundlach, for whose skill and ability I have great 
respect, either intentionally, to simplify his article, or else acci- 
