The strong concave glasses and cheap contact lenses required by myopes of high degree make all objects seem much smaller than they really are, while convex glasses enlarge them. These are unpleasantnesses that cannot be overcome. Patients with high degrees of astigmatism suffer some very disagreeable sensations when they first put on glasses, for which reason they are warned to get used to them at home before venturing out.

Usually these difficulties are overcome, but often they are not, and it sometimes happens that those who get on fairly well with their glasses and discount contact lenses in the daytime never succeed in getting used to them at night.

All glasses contract the field of vision to a greater or lesser degree. Even with very weak glasses patients are unable to see distinctly unless they look through the centre of the lenses, with the frames at right angles to the line of vision; not only is their vision lowered if they fail to do this, but annoying nervous symptoms, such as dizziness and headache, are sometimes produced. Therefore they are unable to turn their eyes freely in different directions. It is true that glasses are now ground in such a way that it is theoretically possible to look through them at any angle, but practically they seldom accomplish the desired result.

The difficulty of keeping the glass clear is one of the minor discomforts of glasses, but it is nevertheless a most annoying one. On damp and rainy days the atmosphere clouds them. On hot days the perspiration from the body may have a similar effect. On cold days they are often clouded by the moisture of the breath. Every day they are so subject to contamination by dust and moisture and the touch of the fingers incident to unavoidable handling that they seldom afford an absolutely unobstructed view of the objects regarded.

Likewise, reflections of strong light from eyeglasses are often very annoying, and in the street may be very dangerous.