Diagnosing Dry Eye in Dogs with the Schirmer Tear Test

Dry eye in dogs is a common condition. When this symptom lasts for a while or becomes a concern, a Schirmer tear test is performed to see if the dry eye is due to a decrease in tear production.

Dry Eye in Dogs Explained

Keratoconjunctivitis sicca (KCS) is the scientific term used when a dog has dry eye and has an inflamed cornea and conjunctiva. The cause of this is the inability of a dog to make enough tears naturally. This is usually caused by nerve damage to the glands that make tears, injuries to the glands, an abnormal reaction from the dog's immune system, an infection or a reaction to sulfonamides. There are also times when the cause behind a dog’s dry eye problem cannot be found.

One of the most common symptoms of dry eye in a dog is a yellow discharge from the eye, because of the accumulation of various particles like dust, pollen and bacteria that can’t be flushed out. A dog with dry eye will also squint, have red eyes and a very visible third eyelid.

How the Schirmer Tear Test Is Performed

The Schirmer tear test measures a dog's tear production to see if his eyes are moist enough. The tear test is quite simple and safe, and does not require any anesthesia. A special test strip that resembles litmus paper is placed into a dog’s lower eyelid (or conjunctival sac), making contact with a dog's cornea. The Schirmer tear test usually isn't painful for a dog, especially if his eye has been numbed before the test. The test can be somewhat uncomfortable for a dog if his eyes are already in pain. Some veterinarians will administer a topical anesthetic to numb the eye in order to prevent tearing due to the irritation from the strip of paper. Numbing the eye, however, can alter the test results.

The test strip has numbers on it like a ruler. Once the strip is in a dog's eye, the dog's eyes are closed shut and it’s left there for one minute per every 15 mm of test strip, and it's then removed. If a dog produced any tears, the paper will absorb them and indicate the quantity of tears produced. The Schirmer test's measurements are determined by how much color is seen on the tear-stained paper.

  • A test strip of a dog with normal tear production will stain the test strip up to at least the 15mm mark.
  • If the color on the test strip reaches 10 to 14mm, the result is considered borderline.
  • A dog is diagnosed with dry eye if the stain on the test strip only reaches 10 mm or less.
  • Severe dry eye is diagnosed when the measurement reaches 5 mm or less.

The Schirmer tear test is a simple way to measure the moisture level of a dog's eye and his tear production. After a dry eye diagnosis is made, a dog can then begin an artificial tear treatment that corresponds with the severity of the condition.