Globally, 19 million children are living with vision impairment
and approximately 12 million children have a significant, uncorrected refractive error . Children in China are affected about 78% of myopia . In Vietnam, the percentage of children with refractive errors is from 15-40 %, and about 3 million children needed glasses . The ratio of Ophthalmologist/Optician /1000 people in Vietnam are low. In training refractive errors for optician some considerations are necessary. This paper introduces some formula for explaining in diagnosis refractive errors for optician in practice.