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Monica Motta, Peter Strom, Katarzyna Paschalis Trela, Andrea Rodrigues, Christopher Murphy; Normative Values for the Tear Film of the Rabbit, Dog and Human. Invest. Ophthalmol. Vis. Sci. 2013;54(15):965.
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The formation and the dynamics of tear films (TFs) are essential for maintaining the health of the ocular surface. Abnormalities in the quantity and/or quality of the TF may compromise these essential functions. The development and utilization of newer imaging techniques enable more accurate assessment of the TF than was previously possible. The literature describing the TF focuses predominantly on the TF of the human with comparative studies being widely disseminated across diverse journals and books. TF attributes such as thickness and composition are poorly documented in the great majority of vertebrate species, including domestic and lab animal species. The objective of this review was to create an accessible compilation and comparison of normative quantitative and qualitative ocular tear film data in 3 different species. The human and two common models in eye research, the dog and the rabbit.
Normative data on TF dimensional values, dynamics, components and properties on all three species were collected through searching online publication databases, as well as books and journals available to the authors. The data were then compiled, organized and evaluated.
Significant differences in TF thickness were identified between human and rabbit (35-45μm vs. 9.6-10.5μm). There is wide variation published for human TF thickness (5.1 ± 0.5μm through 35-45μm). The values reported varied with measurement technique. We were unable to find any studies on the entire canine TF thickness but identified reports on the thickness of individual layers. The thickness reported for the lipid layer varied widely for both the canine and human and was technique dependent (0.013-0.586μm; 0.04-0.814μm reported for the dog and human, respectively). The reported value for the rabbit was approximately 0.180 μm. Similarly, a range for tear protein values were reported with values obtained influenced by the methods used (dog, 2.9-13 g/l; human, 4.21-9.4 g/l; rabbit, 5.4 - 8.2 g/l).
Normative data are essential for providing a basis for comparison in animal models of tear dysregulation as well as assessment of animals with spontaneous TF disorders. This review summarizes the data available in the distributed literature and highlights the need for complete characterization of the normal TF, using identical methods in species used for developing and assessing models of TF disorders.
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