The lacrimal glands are responsible for producing tears that clean and lubricate the eyes. If tear production is decreased or inhibited, the eye can become irritated, scratchy, and sensitive to light. Vision may also be affected. The Schirmer tear or lacrimation test is used for eyes with chronic ulcers and those in which the cornea appears dry on examination.

A vet inserts the tear test strip (a small thin rectangular paper strip) under the lower eyelid. The strip is removed after one minute and the length of the moist end is measured. Strips are frequently saturated in horses after one minute. A very short length of saturation (less than 10 mm of wetting per minute) are diagnostic for tear deficiency.