除了完全失明之外，还有功能性失明。 功能性失明的定义因一个国家而异。 在美国，它指的是视力障碍，即配戴眼镜的最佳矫正效果较好的眼睛的视力低于20/200。 世界卫生组织将失明定义为将最佳眼睛的视力矫正为不超过20/500或少于10度的视力。 功能上失明的人看到的东西取决于失明的严重程度和障碍的形式。 从法律上讲是盲目的：一个人也许可以看到大型物体和人物，但是它们没有聚焦。 合法盲人可能会在一定距离内看到颜色或清晰地看到焦点（例如，能够数指在脸前的手指）。 在其他情况下，色敏度可能会丢失或所有视线模糊。 经验是多变的。 拥有20/400视力的乔伊告诉ThoughtCo，他“一直看到霓虹灯斑点总是在移动和改变颜色”。
新加坡国立大学Medical Assignment代写：严重程度
In addition to total blindness, there is also functional blindness. The definition of functional blindness varies from country to country. In the United States, it refers to visual impairment, which is the best corrective effect of wearing glasses with a vision of less than 20/200. The World Health Organization defines blindness as correcting the vision of the best eye to a vision of no more than 20/500 or less than 10 degrees. What a functionally blind person sees depends on the severity of the blindness and the form of the obstacle. Legally blind: a person may see large objects and characters, but they are not focused. A legally blind person may see color or see the focus clearly within a certain distance (for example, the number of fingers in front of the face). In other cases, color sensitivity may be lost or all lines of sight may be blurred. Experience is changeable. With 20/400 vision, Joey told ThoughtCo that he “always sees that neon spots are always moving and changing colors.”