Schirmer's test detects abnormality of which nerve-

This test measures total tear secretion and normal value is more than 15mm. Schirmer's test determines whether the eye produces enough tears to keep it moist. This test is used when a person experiences very dry eyes or excessive watering of the eyes. It poses no risk to the subject. A negative (more than 10 mm of moisture on the filter paper in 5 minutes) test result is normal. Ref. Ak khurana 6th edition