Reference values, intertest correlations, and test-retest repeatability of selected tear film tests in healthy cats

Abstract

Objective—To determine reference values, intertest correlations, and test-retest repeatability of Schirmer tear test 1 (STT-1), phenol red thread test (PRTT), tear film breakup time (TFBUT), tear osmolarity, and meibometry in healthy cats. Design—Evaluation study. Animals—135 healthy domestic cats aged 0.5 to 12.8 years. Procedures—Each test was performed once in 120 cats and repeated in 40. Pearson correlation was used to assess correlation among tests. Intraclass correlation coefficients (ICCs) and 95% limits of agreement (LOA) were used to evaluate test-retest repeatability. Results—Median (95% central range) values were 18 mm/min (9 to 34 mm/min) for STT-1, 29 mm/15 s (15 to 37 mm/15 s) for PRTT, 12.4 seconds (9.1 to 17.7 seconds) for TFBUT, 322 mOsm/L (297 to 364 mOsm/L) for osmolarity, and 32 meibometry units (MU; 11 to 114 MU) for peak meibometry value. The STT-1 and PRTT values were positively correlated. Age was weakly associated with TFBUT and osmolarity. Meibometry measurements were higher for strips that contacted the tear film (285 MU) than for those that touched the eyelid margin only (32 MU). All ICCs were < 0.75, and 95% LOA were wide. Conclusions and Clinical Relevance—Tear deficiency should be suspected in cats with STT-1 < 9 mm/min, PRTT < 15 mm/15 s, or TFBUT < 9 to 10 seconds. Generally poor correlation among tests suggested that thorough tear film analysis requires performance of multiple tests in concert. Relatively poor test-retest repeatability should be considered when repeated tests are used to monitor tear film dysfunction and response to treatment.

Pilot evaluation of the circadian rhythm of tear production in a population of healthy adult cats

“…This value showed that the STT had poor repeatability in cats (Table ). Although this range was approximately half the previously reported values, it is still a large variation for STT‐1 values (10.4 mm/min). Despite this fact, STT is the most common and conventional method for evaluation of aqueous portion of tear film and should be interpreted in combination with clinical signs in cats…”

“…In the present study, ICC also showed poor test reliability (values <0.40) . Higher ICC values and narrower range of 95% LOA suggest good reliability of a test . The maximum and minimum ranges for 95% LOA were −0.5 to 9.9 mm/min (10.4 mm/min) and 3.3 to 5.3 mm/min (2 mm/min), respectively.…”

“…Schirmer tear test (STT‐1) has been reported to have poor test‐retest repeatability in cats which suggests that this test is not reliable for evaluating disease progression . There are a number of reasons suggested for poor test‐retest repeatability such as patient anxiety, ambient humidity and temperature, change in instrument, and examiner consistency .…”

“…Intraclass correlation coefficient (ICC) was used to evaluate test‐retest reliability . 95% limits of agreement (LOA) were calculated for absolute reliability as the mean difference ± 1.96 × SD differences between baseline values (day 1, 12 am ) and obtained values from each time point …”

Evaluation of lacrimal production, osmolarity, crystallization, proteomic profile, and biochemistry of capuchin monkeys’ tear film

“…for dogs, cats, and horses, with differences attributed to microcomponents of the tear film. 14,[31][32][33] Osmolarity in the human volunteers…”