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

Lionel Sebbag Dr Med Vet1, Philip H. Kass DVM, MPVM, PhD2, and David J. Maggs BVSc3
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  • 1 William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.
  • | 2 Departments of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.
  • | 3 Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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.

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.

Contributor Notes

Supported by the Winn Feline Foundation and the University of California-Davis Center for Companion Animal Health. Financial support was also provided by the Toots and Cello funds. TearLab provided the osmometry test cards, Aca Derm Inc provided the Meibometer test loops, and Merck Animal Health provided the Schirmer tear test strips.

Presented in abstract form at the Annual Meeting of the American College of Veterinary Ophthalmologists, Rio Grande, Puerto Rico, November 2013.

The authors thank Debbie Bee, Dr. Tracy Drazenovich, Zoe Williams, Katherine Kim, Olivia Glass, Jason Wei, Felicia Gary, Madison Herrick, Christina Ball, Kailey Beckman, Jessica Lin, and Joanne Chan for technical assistance and John Doval and Dr. Tomo Wiggans for image preparation.

Address correspondence to Dr. Maggs (djmaggs@ucdavis.edu).