Most healthy persons can do one saccade (a back and forth movement of the eyes with the C-Rod) - per second for 30 seconds free of distress.
A person with a concussion will not make it to 30 seconds - they may get to 4 or 8 cycles before they drop the C-Rod, cradle their head and say they cannot complete the task. Some will then cry or say they are going to be sick. This happens at the time of injury and without therapy can last a lifetime.
When it comes to concussion - they eyes don't lie.
Testing saccadic eye movements are a part of the concussion screening armament but should never be used in isolation of other concussion assessment protocol.
Most examiners will hold up two pencils to do this test. The result is that target distances will vary and the pencils are not likely to be on-plane and may not meet VOMS. The C-Rod provides a standardized 40 cm target distance with high contrast targets on a fixed plane and can be used on five axes to target the activity of three cranial nerves.