The definition of partial sight varies from country to country.

In the UK, the legal definition is "substantially and permanently handicapped by defective vision caused by a congenital defect, illness or injury"

The optical profession has defined this further by using a value that can be measured by standard tests: a visual acuity of 3/60 to 6/60 with full visual field (breadth of vision), or 6/24 or worse, with moderate visual field, or 6/18 or better with very reduced visual field (breadth of vision).