GUIDE 02 / 07
How Closely Are Static and Dynamic Visual Acuity Related?
If your eye chart acuity is good, is your dynamic vision good too? We explain research showing the relationship weakens as speed increases, and the eye's tracking ability that governs dynamic vision.
Static visual acuity is how small a detail you can make out on a stationary optotype. Dynamic visual acuity is your score when that optotype is moving. Since both use the same eyes, they seem like they should be related — but the research is a bit more complicated.
Similar when slow, different when fast
A study by Burg (1966) of drivers in California, USA, reported a high correlation between static and dynamic visual acuity test scores, but found that the correlation shrinks as the target gets faster. In the same study, acuity dropped as target speed increased and as age increased.
Here's what that means. A slowly moving target is easy for the eye to track, so it effectively becomes similar to a static acuity test. With a fast target, how well the eye can track it becomes a new variable, creating individual differences that static acuity alone can't explain.
What governs dynamic vision: pursuit eye movement
To see a moving target clearly, its image needs to stay on the center of the retina (the fovea). To do this, the eye combines a smooth pursuit movement that follows the target and a fast saccadic movement that catches up to it. If the eye can't keep up, the image slides and blurs on the retina, making it harder to make out detail.
Uchida et al. (2012) compared the DVA of 8 college baseball players and 8 non-athletes. When free to move their eyes, the athletes could read smaller optotypes at higher speeds (an average of 404 °/s versus 315 °/s), but there was no difference between the two groups when fixating on a single point. The researchers concluded that the athletes' superior DVA came from the ability to track a target with their eyes, rather than from processing a moving image on the retina.
Still, static acuity is a prerequisite
While static acuity doesn't fully explain dynamic vision, if things look blurry, a moving target will naturally be hard to make out too. If nearsightedness or astigmatism isn't corrected, dynamic vision measurements will also come out lower. Take the test with whatever glasses or lenses you normally use.
Relationship to this site's test
- The target in DVA mode is drawn intentionally large (44 px in diameter). This is because on a typical screen at a 60 cm distance, the gap corresponding to 1.0 decimal acuity (1 minute of arc) is smaller than 1 px and can't be drawn. So this test mainly measures the ability to track something fast rather than to see something small.
- When you calibrate your screen, the result screen also shows what static acuity the target size corresponds to. The lower this value (the larger the target), the smaller the influence of static acuity.