Difference between revisions of Visual acuity
Jump to navigation
Jump to search
→Reading a Snellen chart
| Line 22: | Line 22: | ||
With text that we are familiar with, the brain may clear up that text more than our vision would actually allow. | With text that we are familiar with, the brain may clear up that text more than our vision would actually allow. | ||
20/20 is "good enough" for most purposes, but not "perfect" in any way. Rather, 20/20 vision is slightly defective. It is possible to have 20/20 vision with 0.25 to 0.5 D of defocus, and 20/20 does not imply clear or sharp vision. As [[normalized]] correction typically | 20/20 is "good enough" for most purposes, but not "perfect" in any way. Rather, 20/20 vision is slightly defective. It is possible to have 20/20 vision with 0.25 to 0.5 D of defocus, and 20/20 does not imply clear or sharp vision. As [[normalized]] correction typically imposes 0.25 D of extra myopic defocus on [[20/20 correction]], it can be considered to be 0.25 to 0.75 D of undercorrection. | ||
Tscherning writes in ''Physiologic Optics: Dioptrics of the Eye, Functions of the Retina, Ocular Movements and Binocular Vision'': | Tscherning writes in ''Physiologic Optics: Dioptrics of the Eye, Functions of the Retina, Ocular Movements and Binocular Vision'': | ||