(Winn-funded study)
There are very few reports available about tear evaluation in cats alongside recent information about eye disease in cats in general. Tears provide comfort through
keeping the surface moist plus tear film helps provide nutrients and protection against pathogens and debris. There appears to be increasing indication that quantitative (amount of tears produced) and qualitative (characteristics or makeup of tears) tear film deficiencies play an important role in many eye diseases in cats. These deficiencies may be a cofactor or cause in some of the most common and frustrating ocular diseases such as KCS (keratoconjunctivitis sicca), chronic nonhealing corneal ulceration, corneal sequestration, conjunctivitis and keratoconjunctivitis following feline herpesvirus-1 infection.
The authors’ objective with this study was to determine reference values, intertest correlations, and test-retest comparisons for 5 different diagnostic tests used to evaluate tear film. The tests include Schirmer tear test 1 (STT-1), phenol red thread test (PRTT), tear film breakup time (TFBUT), tear osmolality, and meibometry performed in 120 cats at least once and repeated in 40.
The results indicated that tear deficiency should be suspected in cats with values of a STT-1 < 9mm/min, PRTT of <15 mm/15s, or TFBUT of < 9 to 10 seconds. There was no significant difference in test results between right and left eyes. SST-1 values were not affected by age or sex of the cats evaluated. Taken with the study’s data and facts that indicate tear osmolarity does not differ between cats with or without conjunctivitis, tear film osmolarity in cats has an inherent variability that reduces its diagnostic benefit to cats. The measurement results for meibometry were higher in strips that contacted tear film than those in contact with eyelid margins. The test-intertest comparisons had generally poor correlation leading to the authors’ suggestion that a thorough tear film analysis requires performance of multiple tests in concert.
One of the most clinically important findings from this study was the poor test-retest repeatability across all the diagnostic assays evaluated. This suggests the use of any of these assays for monitoring disease progression or efficacy of treatment may not be reliable. In humans, this type of diagnostic testing is often more reliable in people with quantitative and qualitative tear deficiencies. Therefore, it is warranted to evaluate test values, correlation, and test-retest reliability in cats with ocular surface disease following this study’s evaluation and results in healthy cats.
