It can be argued that since color is a major part of the perception of form it follows that in small to medium sight defects form is not as well perceived with glasses. Secondly its possible that glasses actually agravate the eye, by constantly maintaining a degree of refractive error which otherwise would not be there, particularly while in eccentric focusing. The strong concave glasses required by myopes of high degree make all objects seem much smaller than they really are, while convex glasses enlarge them. Patients with a degree of astigamitism can suffer some very disagreable sensations when they put on glasses. Usually these difficulties are overcome, but often they are not, and it sometimes happens that those who do overcome them during the day never succeed in getting used to them at night.
All glasses contract the field of vision to a greater or lesser degree.
Often glasses cause annoying nervous symptoms, such as dizziness and headache, and the frames also interfere with peripheral vision. Many Russian civilians during WW2 were known to wear negative diopter lenses for several days prior to visual examinations in compuslory enlistments in order to easily fail the tests. Refractive abnormalities are continually changing from day to day, from hour to hour, and from minute to minute. A fact that is easily verified by personal observation. Thus the accurate fitting of glasses or contacts is, of course impossible.