Least distance of distinct vision
（重定向自Distance of distinct vision）
![](/Images/godic/202501/09/Focal-length2117.png")
In optometry, the least distance of distinct vision (LDDV) or the reference seeing distance (RSD) is the closest someone with "normal" vision (20/20 vision) can comfortably look at something. In other words, LDDV is the minimum comfortable distance between the naked human eye and a visible object.