Your vet measures your dog's tear production using a Schirmer Tear Test. It is not uncomfortable for your dog and no sedation or anaesthetic is needed. A special strip of paper is placed in the eye, and tear production assessed. The results are immediate.
Both eyes should be tested as the results are often quite different.
The results of the test are interpreted with other findings, such as clinical signs, to determine whether Dry Eye is present. If your dog has Dry Eye, they are not producing sufficient tears and should start treatment immediately.
Schirmer Tear Test (STT)
Watch this video to see a demonstration of a Schirmer Tear Test