Difference between revisions of Visual acuity
Jump to navigation
Jump to search
no edit summary
No edit summary |
|||
| Line 1: | Line 1: | ||
Visual acuity (VA) is the measurement of how well the entire vision system can recognize what it sees. Formally, it is defined as the reciprocal of the smallest angle that the visual system can resolve. | Visual acuity (VA) is the measurement of how well the entire vision system can recognize what it sees. Formally, it is defined as the reciprocal of the smallest angle that the visual system can resolve. | ||
It will depend on the amount of defocus that [[accommodation]] cannot overcome | It will depend on the amount of defocus that [[accommodation]] cannot overcome because it is outside of the focus range or due to other defects such as [[astigmatism]]. Defocus causes [[blur]] and [[double vision]]. | ||
For distance, this is typically measured with a [[Snellen chart]] and expressed as the distance you need to be from the chart to recognize the characters over the distance that someone with normal vision can recognize the characters. Lens or mirrors may be used to change the effective test distance in a smaller room. | For distance, this is typically measured with a [[Snellen chart]] and expressed as the distance you need to be from the chart to recognize the characters over the distance that someone with normal vision can recognize the characters. Lens or mirrors may be used to change the effective test distance in a smaller room. | ||