214 Dr. Hosacks Observations on Vision. 
effect, as they are not at all connected with the nature of this 
disease. 
But the action of the external muscles, I apprehend, will 
afford us a satisfactory explanation vv’,en the eye is turned 
from its natural direction, for example, owards the inner 
canthus, it is obvious that the adductor muscle is shortened, 
and its antagonist, the abduct jv, lengthened; consequently, as 
the abductor has not the same power of contracting itself with 
the adductor, when the eye is directed towards an object, their 
power of action being different and irregular, the compression 
made upon the eye and its humours must also be equally irre- 
gular, and therefore insufficient to produce the regular changes 
in the refraction and shape of the eye we have shewn to be 
necessary in adapting it to the different distances of objects. 
The effects produced by making a partial pressure upon the 
eye with the finger, or speculum oculi, before noticed, would 
also appear to favour this explanation. 
Thirdly. May it not in part be owing to the loss of this com- 
bined action of the external muscles, and the difficulty of re- 
covering it, that the operation of couching is sometimes un- 
successful, especially when the cataract has been of long 
standing ? This cannot be attributed to the iris, for it per- 
haps, dilates and contracts as before : nor to the muscles of 
the lens, for they are removed ; nor to the state of the nerve, 
for it is still sensible to light ; and yet the patient cannot 
see objects distinctly ; and it is not an uncommon circumstance, 
even when the operation succeeds, that the sight is slowly and 
gradually recovered. Instances have occurred, Mr. Bell* 
* See his System of Surgery. 
