What is this eye exam for?

Question

Last time I went to the eye doctor, I had to look into a machine. The inside was dark except for one green 8-sided star.

At first it was out of focus, then the technician did something and it slowly came into focus. Then she restarted it and it was out of focus again. She did this about 3 times.

What was this testing for?

Answer 1

Sounds like an autorefractor to me.  It basically determines your prescription while you focus on an image.  Doctors usually use the results as a starting point for their own refractions.  Another possibility is an autokeratometer.  It determines the curvatures of your corneas (the K readings), which are used in fitting contact lenses and checking for things like keratoconus.

Answer 2

i'm thinking...color blindness.....

Answer 3

This sounds like it was the machine that does the reading of your prescription. Before the doctor examines you they do a reading of your prescription so the doctor has a starting point. Or it could be the machine that checks your pheriphal vision. But from the way you describe it, it really sounds like the one that reads the prescription. Don't quote me on this but if I remember right it's called a K reading.