GUIDE 01 / 07
What Is Dynamic Vision — The Difference Between DVA and KVA
DVA measures a target passing by sideways, KVA measures a target approaching head-on. Here's what each measures and how it's tested.
Visual acuity measured by an eye chart is about how small a detail you can make out on a stationary target. But when hitting a ball or driving a car, most of what we look at is moving. The ability to make out detail on a moving target is broadly called dynamic vision, and research and testing usually split it into two kinds.
DVA — A target moving sideways
DVA (dynamic visual acuity) is the ability to identify a target moving sideways (horizontally, vertically, or in a circular path) while staying at roughly the same distance from the observer. Tests commonly move an optotype like a Landolt ring at a constant angular speed and use the highest speed at which the gap's direction can still be identified as the result. The unit is °/s (angle per second) or a device-specific unit (such as revolutions).
- This relates to things like reading a license plate on a passing car, or a ball darting sideways in table tennis or tennis.
- The eye's ability to track a target (pursuit eye movement) plays a large role in the result.
KVA — A target approaching head-on
KVA (kinetic visual acuity) is the ability to identify a target approaching or receding head-on, a measure developed in Japan. Under the standard set by Japan's National Police Agency for dynamic vision testers used in courses, an optically produced four-direction Landolt ring approaches from about 50 m to 2 m at 30 km/h (the ring size corresponds to 1.0 visual acuity at the 30 m position), and the test taker answers with a lever or button the moment they identify the gap's direction. The dynamic vision value is calculated from the position at that moment, repeated 5 times and averaged.
- This relates to things like an approaching ball, or a car or sign ahead as the distance shrinks.
- Since apparent size grows inversely with distance as a target approaches, the farther away (the smaller) you can identify it, the better the result.
At a glance
| Category | DVA | KVA |
|---|---|---|
| Target's movement | Moves sideways (distance roughly constant) | Approaches head-on (distance decreasing) |
| Typical result | Highest angular speed read (°/s) | Size at the moment read → decimal acuity |
| Better result | Higher speed | Smaller size (identified farther away) |
| Mainly used in | Sports vision research | Japan's driving aptitude tests · sports research |
The two modes on this site
This site's Horizontal Movement (DVA) mode moves a target from one edge of the screen to the other at a constant speed, raising the speed by 1.2× each time you get it right to find the highest speed you can read. The Approaching Target (KVA) mode grows the target as if it's approaching at a constant speed (apparent size ∝ 1/distance), and records the diameter at the moment you press.
Neither replaces a professional tester, since a screen's refresh rate, size, and brightness aren't controlled. Instead, you can use them to track your own changes by repeating under the same conditions.