Corey was classified as legally blind due to an inherited disease called Leber's congenital amaurosis. Reading in school or riding a bike came with high degree of difficulty for him.
Corey's father, Ethan Haas, said it was "heartbreaking" to learn his son had the congenital disease.
However, when the Haas family learned about an experimental vision procedure from a doctor in Boston, Corey said he was "all for" anything that would help him see better.
The gene therapy trial at The Children's Hospital of Philadelphia changed everything for Corey and his family.
Corey received a procedure in which scientists use DNA from a DNA bank to create a functioning gene, which Corey was missing. The gene was then injected into his eye with a thin needle. The new gene will make a missing protein inside Corey's faulty retina to help restore his vision.
Though Corey said he was scared of the procedure, he began seeing changes just four days after it.
Corey told CBS News, "It's sort of amazing that I can see the colors better than before the surgery."
In fact, following the procedure, Corey could complete a vision obstacle course that previously took him four minutes to complete in just a few seconds.
"His independence has increased, and he's able to play like a normal child now," Corey's father, Ethan said. "(He can) just run around, play, and (we don't) have to worry about him tripping over everything."
Dr. Steve Rose, chief research officer for the Foundation Fighting Blindness that supported the research for Corey's procedure, said the foundation is trying to make the procedure widely available.
"There are lots of clinical trials ongoing, and this really sets the stage for many more diseases -- retinal diseases and eye diseases -- going forward."
For more information about this type of gene therapy and Corey's story, go to The Children's Hospital of Philadelphia's press release information page.