[Logarithmic visual acuity charts: reasons to use and how to design it]

Visual acuity represents the visual angle or the smallest distance between two points that allows their discrimination as separated points. Although it is the most common clinical measurement of visual function, it is often misunderstood, especially due to the variety of charts and different notation systems employed for its quantification. This article reviews some concepts about visual acuity measurement, the main notation systems, type of charts and discuss the advantages of using logarithmic scales.