That's why doctors rely on cognitive testing to check brain function.
"Most of the neuropsych tests that we give are sort of like puzzles and games and brain teasers. With the computerized tests, they're even more so like video games," says Christopher Bailey, Ph.D., a neuropsychologist at University Hospitals.
UH uses the military designed ANAM test, otherwise known as the Automated Neuropsychological Assessment Metric.
By fall, student athletes from Laurel, Hathaway Brown, Hawken, Beaumont, Lake Erie Community College and Case Western Reserve University will take the test at UH for a baseline evaluation.
If they get a sports concussion during their season, they must take the test again to check progress.
"The neuropsych testing provides an objective measure. You can't fake 'good' on the neuropsych testing. Your thinking is back to where we expect it to be or it's not," says Dr. Bailey.
Susannah Conway wishes she had access to it in 2008 before a concussion during a soccer game sidelined her permanently.
"I had a lot more trouble concentrating than usual. Simple things, like walking up the stairs, would make my head hurt," Susannah says.
Physical recovery took her two months but one hit was all she could take. Her short-term memory was affected for months.
Dr. Bailey estimates about 20 percent of the athletes they'll test will return with a concussion.
Cleveland Clinic, along with Akron Children's Hospital and Summa Hospitals, have used a similar test for the last few years. It's basically the same premise as ANAM but this one is called Impact, or Immediate Post Concussion Assessment and Cognitive Test.
All college and high school athletes covered by Cleveland Clinic Sports Health take the test, which can be done in about 25 minutes, at the beginning of the season, and then they take it again in the event of a concussion.
Even when the physical symptoms have healed, the brain can still be damaged. The test can check reaction time and thinking skills. As of now, these tests are the best tools out there but research is ongoing.
"There are genetic studies being done at different institutions around the country, looking to see if there are markers that we can use to help predict people who won't do as well," Dr. Paul Gubanich, of Cleveland Clinic Sports Medicine says.
For now, trainers, coaches and the athletes themselves are on the front line of defense against concussions. And even though it's an invisible injury to the eye, awareness is the best play for prevention.
"The NCAA has announced that they're going to have new concussion management programs and guidelines and we see some of the professional teams and the NFL is changing some of their management strategies too," Dr. Gubanich says.
The NCAA now does not allow an athlete to return to the same game in the event of a hard head hit and they must be evaluated.
Dr. Gubanich will attend the NFL's conference on concussions in June and he anticipates similar protocols will be enacted.