Before revision: From the thin lens formula, the required lens will have optical power given by The calculation can be further improved by taking into account the distance between the spectacle lens and the human eye, which is usually about 1.5 cm: .
After revision: From the thin lens formula, the required lens will have optical power given by The calculation can be further improved by taking into account the distance between the spectacle lens and the human eye, which is usually about 15 cm: .