The tags have the diopter number plainly written. Only the symbol of plus is omitted. They seem like price numbers. In olden times they may have known better. If you disregard the inch number you can readily tell, in diopters, what strength each pair of glasses has. You would know what you are looking for.
Ready-to-wear glasses are plus and spherical. Therefore, they can do no harm to your eyes or vision. It is only minus lenses or cylinder lenses that may do you harm if fitted wrongly. The minus lenses can, mainly, be harmful if used for near seeing. The cylinder lenses can be harmful if too much cylinder is given, and if the axis is not set in the right position.
Plus spherical glasses are always beneficial for nearer vision. Also, they will do you no harm, rather they will do your eyes good if you wear them for distance, even when you can see better with the naked eyes. Plus spherical glasses relax and strech your eyes. They give your eyes a posture similar to star-gazing. And the posture of star-gazing is what the eyes of civilized human beings need and what they do not have.
Ready-to-wear glasses can be had from one-quarter of a diopter up to five diopters--symbols 0.25 up to 5.00. The weaker numbers, 0.25 up to 1.25 can safely be used by children and adults up to the age of forty-five or older. They are a positive help in near-seeing and many benefits may be had by their use for distant seeing. The stronger numbers of glasses are, mainly, used by older persons for reading and other near work. Also, they are used by the higher grades of hyper-sighted eyes (see Lesson 16) which require stronger plus glasses.