# Strip Consistency Tube in the Assessment of Tear Lactoferrin in Non-Obese Diabetic (NOD) Mice
## 4 Discussion  
Experimental settings using dry eye mouse models are necessary to elucidate the pathophysiology of dry eye disease and to help with the development of new treatment modalities and agents. Strip meniscometry has been shown to be a reliable method of measuring the tear meniscus volume and to have a strong correlation with tear function tests and vital staining scores in humans [4; 5; 6; 8]. Previously, we have shown that the SMT test was quite efficient in measuring tear volumes in wild type and an environmental stress dry eye mouse model [13], where this testing was observed to be well correlated with other tear function parameters. This previous report emphasized the stability of the material while holding, the overall convenience of the technique, and the short measurement time as advantages of this new methodology [13]. In this investigation, we attempted to study if SMT could be used for the assessment of tear proteins. We have decided to concentrate on tear lactoferrin this time, which is known to be reduced in tears in dry eye disease and [PERSON] syndrome [14; 15]. Moreover, a previous clinical investigation conducted by us demonstrated that lactoferrin was an efficient treatment modality in improving tear stability and ocular surface epithelium in dry eye patients with [PERSON]'s syndrome [16]. We employed NOD mice in this study because this model has been shown to harbor the clinical dry eye and ocular surface characteristics as observed in [PERSON]'s syndrome [2; 17]. The results of the current investigation showed that SMT could detect the tear volume differences between the WT and NOD mice, which was significantly lower in the latter. The NOD mice also had a significantly higher extent of ocular surface epithelial damage when compared to the wild-type mice. To our surprise, we found that tears collected with SMT harbored sufficient lactoferrin detectable by ELISA testing, also suggesting that SMT testing could reveal lactoferrin concentration differences between the SS model mouse and the wild-type mouse.  
While our observations should be retested in a large number of NOD mice and other models of mice with dry eye disease, the initial findings of the current study pave the way to a novel method of tear lactoferrin assessment in murine experimental models. Our findings also justify the SMT testing that is used for the evaluation of other tear proteins or inflammatory markers including cytokines and chemokines. Future testing should also establish sensitivity and specificity of this method in assessing tear lactoferrin concentrations in human subjects and murine models with dry eyes. The new SMT has yet to be tested in human tear lactoferrin concentration assessments, which we believe should be much easier to perform because the human eyes are bigger and SMT testing can be  
Figure 3: Comparison of corneal vital staining scores between NOD and the Balb/c mice. Note the significantly higher staining scores in the NOD mice compared to the WT mouse (\(p\) = 0.03). \({}^{*}\) represents \(p\) < 0.05.  
readily carried out by dipping the tip of the tube into the tear meniscus without touching the lids or the ocular surface. This eliminates the possibility of reflex tearing, which would have an effect on tear protein concentrations. Therefore, one possible shortcoming of the new SMT methodology is that because the mouse eyes are small, the tips of the strips inevitably touch the lids and the conjunctiva, which might induce reflex tearing and alter the concentration of tears. Still, being able to detect tear protein concentration with small amounts of tears collected over 5 s is an important step forward in animal experiments of dry eye disease.