Change in visual acuity is calculated directly by subtracting LogMAR data, while the average visual acuity is obtained with the arithmetic mean value of the LogMAR data. The mean acuity expressed in LogMAR units can be transformed into a decimal chart for a more comprehensive result. To calculate the average visual acuity directly from the decimal data, the geometric mean value must be used instead of the arithmetic mean value.Is 20 40 eyesight good?
Vision of 20/40 is worse than standard vision and sometimes requires glasses, depending on the exact nature of the vision problem, according to Eye Care Fun. Someone with vision of 20/40 can see objects from 20 feet away that someone with normal vision can see from 40 feet away. Normal vision is considered to be 20/20, Eye Care Fun notes.What is best corrected visual acuity?
Best Corrected Visual Acuity (BCVA) Measurement of the best vision correction that can be achieved, such as glasses, as measured on the standard Snellen eye chart. For example, if your uncorrected eyesight is 20/200, but you can see 20/20 with glasses, your BCVA is 20/20.