Altering Eyeglass Selection and Usage
Bi-focal and tri-focal eyeglasses are commonly ground to provide refractory correction ideal for reading, that is, 12 to 24 inches (30 to 60 cm), when the wearer is looking downward through them. These glasses, used for reading, are therefore not ideal for safe walking, where correction for 4½ to 5 feet (137 to 152 cm) would be far more appropriate. Some countries with universal health care recommend separate reading and walking glasses, a rather rare practice in the U.S. in the early 21st Century.
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