48 MYOPIA, TREATMENT.
not one of simple bad habit, but if in connection with distinct vision there exist a high degree of myopia, for instance, M^, it is at all events advisable to remove the far point by concave glasses to about 16 or 18 inches, and then to enforce an object distance of at least 12 or 14 inches.
To insure an erect position of the head, it is advisable in read- ing to hold the book in the hand, and in writing to use a desk with a steeply-inclined and sufficiently high surface. In furnish- ing school-rooms these points deserve careful attention. It is for the interest of society to combat the development of myopia by a proper system of lighting and furnishing school-rooms.*
If a high degree of myopia appear in early youth, it should influence the choice of an occu])ation. It is difficult, however, to lay down positive rules in this matter.
In most cases it is necessary to render distant vision distinct by the use of proper concave lenses. We have already seen that the concave lens whose focal point corresponds with the far point fulfils this condition, and we shall here only repeat that always only the weakest lenses with which distinct distant vision is pos- sible should be used. The question whether the correcting lenses should also be used for near objects has been much discussed. In this matter a general rule cannot be laid down. The question must be decided for each individual case. A myopic eye, provided with the proper concave lens, behaves exactly as an emmetropic one, which indeed is a desirable condition. Nevertheless, it is only under the following circumstances that the neutralizing concave glasses ought to be worn continuously and used for near objects.
1 . The myopia should not be greater than ^ or ^. For low degrees of myopia, under M2^ there is scarcely ever any neces- sity for wearing concave glasses continuously.
2. The range of accommodation must be normal.
3. Vision must be normal.
4. The continuous use of concave glasses must have been begun in youth.
Under these circumstances, there is no objection to the contin-
- Compare Dr. H. Colin, Untersuchung der Augen von 10,060 Schulkin-
dern, nebst Vorschlagen zar Verbesserung der den Augen nachtheiligen Schuleinrichtungen. Leipzig, 18G7, und Deutsche Klinik, 1866, No. T.
