Fig. 3. Six-millimeter arcuate keratotomy nomogram. Optical zone is 6 mm. Knife setting is 100% of thinnest pachymetry at the 6-mm optical zone in the axis of astigmatism. If the patient is older than or younger than 30 years of age, efficacy is increased or decreased 2% per year: age 20 = 80% of age 30; age 55 = 150% of age 30; age 80 = 200% of age 30.