A test called the worth four dot is commonly used during a functional vision exam. The purpose of this test is to determine whether both eyes are looking and are active when they are looking at an object in space. A person can sometimes experience double vision or the brain can shut off one eye's vision if it doesn't want you to focus on a specific image, which can happen if you have an eye turn or if the vision in one eye is worse than the other. This test is a way to check if the brain is turning off vision to that eye and seeing what the patient sees.
Worth four dot test: How does it work?
Patients are placed in a dark room and shown the worth four dot device while wearing red and green glasses. An optometrist is going to hold up the worth four dot device. This device consists of four different colored dots. A red dot at the top, two green dots on the sides, and a white dot at the bottom.
Possible outcomes
A red dot and a white dot: If the patient’s left eye didn't work but their right eye did, and they were looking through the red glass, then those green dots would basically disappear, they would turn black, and they would only be able to see the red and a white dot.
Green dots and a white dot: If the patient’s left eye was working and they were looking through the green glass, they would only be able to see green dots on the sides and the white dot at the bottom.
Double vision: If the patient sees five dots, then this means that they have double vision because in reality, there are only four dots.
Four dots: If both eyes are working, then they should see all four dots like we do without glasses. A test like this is very useful for patients who are shutting off one of their eyes and they are unaware that their brain is shutting off one of their eyes.
