Understanding and diagnosing keratoconjunctivitis sicca (KCS)

The I-TEAR® TEST is an easy and efficient diagnostic tool that can be added to your protocol when treating keratoconjunctivitis sicca (KCS) in your patients.

Keratoconjunctivitis sicca (KCS) or Dry Eye Disease is well documented in humans1; however, this disease can affect dogs and cats as well. KCS is a multifactorial disease of the ocular surface defined by inflammation of the cornea and conjunctiva that leads to instability of the tear film. One would assume that dry eye involves a lack of tear production – a loss of the aqueous solution in the tear film resulting in inadequate nutrients to the surface of the eye.1 However, an animal can also suffer from KCS with an adequate quantity of tears. In this case, the tears produced are of poor quality, not preventing tear film evaporation and therefore not protecting the cornea from drying.

The importance of tears

The cornea itself does not have blood vessels, and thus relies on tears to bring oxygen and nutrients to the cells of the eye. The tear film is made up of three components – the outer lipid layer, the middle aqueous layer, and the inner mucus layer.2

  1. Outer lipid layer – Produced by the meibomian glands, this layer prevents the evaporation of tears, such as a layer of oil on water.
  2. Middle Aqueous Layer – Produced by the lacrimal gland, the aqueous layer contains the necessary water and nutrients to nourish the eye. The largest portion of the tear film, the ‘third eyelid’, produces approximately 40% of the tear film. It sweeps back and forth across the surface of the eye, distributing the necessary nutrients.
  3. Inner Mucus layer – Produced by the conjunctival goblet cells, the mucin layer helps stabilize the tear film and ensures it adheres to the surface of the eye. This layer also protects the underlying epithelium and the eye itself against microbial invasion.
Image 1. Lacrimal gland, Meibomian Gland and the Tear Film
Image 1. Lacrimal gland, Meibomian Gland and the Tear Film

An imbalance with the tear film can result in irritation of the cornea and conjunctiva, infections, and more concerning issues such as ulcers and blindness. Therefore, it is crucial to take note of any discrepancies within the eyes of patients, and quickly diagnose keratoconjunctivitis sicca to prevent further damage to the eye.

How to diagnose both types of KCS

Although there is a focus on diagnosing an aqueous deficiency, evaporative dry eye (a lipid deficiency) is also common. In the early stages of Dry Eye Disease, you may not see the typical yellow ocular discharge2 but your patients can exhibit one or several of the following signs:

  • excessive tearing or blinking
  • red, irritated eyes
  • crusty nostrils (due to a lack of fluid to the nasal punctum)
  • pigmentation of the corneal surface
  • keratitis (inflammation)
  • ulcers and abrasions

When faced with a patient that has any of these symptoms, you may want to consider a test for diagnosing KCS. To test for evaporative DED, the most common diagnostic tool is testing tear breakup time (TBUT). Fluorescein is placed into the patient’s tear film, which is then observed under cobalt blue illumination.4 The number of seconds between the last blink and the appearance of a dry spot in the tear film is recorded as the TBUT, and anything under ten seconds is considered abnormal.4 When testing for volume, two options are available: the Schirmer Tear Test, as well as an alternative and less invasive option – The I-TEAR® TEST. The I-TEAR® TEST is a diagnostic tool that takes five seconds to complete, does not require anaesthetic and provides an accurate quantitative measurement of the volume of tears in your patient’s eyes.3 The test strip has two sides, for left and right, and is placed in the tear meniscus for five seconds as shown in the image below.3

Image 2. I-TEAR® TEST
Image 2. I-TEAR® TEST

Mark the length of the stained tear column and note that anything under a reading of 8mm is considered abnormal tear production. Compared to the Schirmer Tear Test that has a range of diagnostic conclusions, the I-TEAR® TEST is a simple and efficient screening test for any predisposed breeds or patients that exhibit KCS symptoms with better sensitivity and specificity.5

References

1Craig, J. P., Nichols, K. K., Akpek, E. K., Caffery, B., Dua, H. S., Joo, C. K., … & Stapleton, F. (2017). TFOS DEWS II definition and classification report. The ocular surface15(3), 276-283.

2https://www.youtube.com/watch?v=GZnFuWHq6to

3https://imedanimalhealth.com/pages/diagnostic-tools

4Kallarackal, G. U., Ansari, E. A., Amos, N., Martin, J. C., Lane, C., & Camilleri, J. P. (2002). A comparative study to assess the clinical use of Fluorescein Meniscus Time (FMT) with Tear Break up Time (TBUT) and Schirmer’s tests (ST) in the diagnosis of dry eyes. Eye16(5), 594-600.

5Miller, T., Hoffman, I., Dunbar, J. Comparative Tests of the Canine Tear Film Using the I-TEAR® Test and the Schirmer Tear Test [PDF presentation]. https://cdn.shopify.com/s/files/1/2513/4894/files/Miller_study_LB_PDF.pdf?4412641717838339293  

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