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Appendix 1: Terminology |
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Visual acuity
Visual acuity is a measure of the sharpness of vision. The Snellen chart is the most common method of measuring it. A visual acuity of 20/20 (metric 6/6) means the ability to see the 20/20 line at 20 feet away. A visual acuity of 20/40 (6/12) means the ability to see only the 20/40 line clearly from 20 feet away, whereas a person with 20/20 vision should be able to see the same line from 40 feet away. |
Uncorrected visual acuity
The visual acuity measured when a person is not wearing any spectacles or contact lens |
Best spectacle-corrected visual acuity (BSCVA)
The visual acuity measured when a person is wearing the most suitable spectacles to correct the refractive error |
Loss of lines of BSCVA
When a person is no longer able to see the line of the Snellen chart that he or she saw before refractive surgery, some loss of vision has occurred. The amount of loss can be quantified by describing the number of lines lost on the Snellen chart. For example, a change from 20/20 (6/6) to 20/30 (6/9) is a loss of 2 lines of BSCVA |
