According to WHO, blindness is defined as a visual acuity of the better eye, less than
**Core Concept**
Visual acuity is a measure of the sharpness and clarity of vision, and it is an essential parameter in assessing the severity of visual impairment. The World Health Organization (WHO) has established specific criteria for defining blindness and low vision to facilitate global comparisons and monitoring of visual impairment.
**Why the Correct Answer is Right**
According to the WHO definition, blindness is defined as a visual acuity of the better eye, which is less than 3/60 (or 6/60 in some countries). This definition is based on the Snellen visual acuity chart, which is a widely used tool for measuring visual acuity. A visual acuity of 3/60 indicates that the person can only see objects clearly at 3 meters that a person with normal vision can see at 60 meters. This level of visual impairment significantly impairs daily activities and is therefore classified as blindness.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the WHO definition of blindness.
**Option B:** This option is incorrect because it is a common misconception that blindness is defined as a visual acuity of 20/200, but this is actually the definition used in the United States.
**Clinical Pearl / High-Yield Fact**
It is essential to note that visual acuity is only one aspect of visual function, and other factors such as visual field defects, glare sensitivity, and contrast sensitivity can also contribute to visual impairment.
**Correct Answer: D. 3/60**