Parkinson`s affects 1 in 500 people and is the second most common neurodegenerative disease worldwide.
The charity Parkinson`s UK welcomed the research as a "significant step".
The researchers examined rats and found that changes could be seen at the back of their eyes before visible symptoms occurred.
Professor Francesca Cordeiro who led the research said it was a "potentially revolutionary breakthrough in the early diagnosis and treatment of one of the world`s most debilitating diseases".
"These tests mean we might be able to intervene much earlier and more effectively treat people with this devastating condition."
Symptoms of Parkinson`s include tremors and muscle stiffness, slowness of movement and a reduced quality of life.
These symptoms usually only emerge after brain cells have been damaged.
But there is currently no brain scan, or blood test, that can definitively diagnose Parkinson`s disease.
Parkinson`s does not directly cause people to die, but symptoms do get worse over time.
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