The clinical management of DED in dogs can be challenging due to the multiple underlying disease processes that alter tear film quantity and quality, as well as the advanced stage of the disease when dogs are evaluated. Therefore, the use of newer imaging and diagnostic testing may help to establish the diagnosis of DED at an earlier stage, allowing prompt and necessary treatment. Prior to widespread utilization, correlations between more traditional diagnostics tests with newer diagnostic modalities, particularly in healthy and DED-affected brachycephalic dogs, is necessary. When correlated, STT-1 and I-Tear test showed a moderate and not significant correlation only for dogs with severe dry eye, while the correlation was weak in the other groups. Previous studies have shown a strong correlation between STT-1 and I-Tear test in dogs with KCS (Miyasaka et al. 2019; Nascimento et al. 2022). This correlation is stronger with increasing severity of tear deficiency. Another study reports a weak positive correlation between these tests (Rajaei et al. 2014). However, these previous studies were performed also on dolichocephalic and mesocephalic breeds, not just brachycephalic as in our study.
In our study, the results of the TBUT and TBUTNI (OSA-Vet®) tests, with median values of 3(6)s and 3(6.25)s for TBUT and TBUTNI respectively, were below the reported reference values for dogs with normal STT-I (Featherstone and Heinrich 2021). Other studies have reported a mean TBUT of 5.3±2.4s in the ShihTzu (Sebbag et al. 2022) breed, and 6±2s and 5.4±1.9s for the right eye and left eye, respectively, in brachycephalic breeds (Jeong et al. 2022). A study performed exclusively in healthy Pug dogs had TBUT values that were consistently higher than those found in our study (Labelle et al. 2013). Therefore, our study reveals that brachycephalic dogs in the HD group exhibited reduced TBUT values compared to the literature's reported average TBUT time for dogs in general, which typically falls between 19.7±5s and 21.53±7.42s (Featherstone and Heinrich 2021; Faghihi and Rajaei 2023). This difference could stem from various factors including examiner subjectivity, environmental conditions (such as temperature and humidity), and the quantity of fluorescein applied during the TBUT assessment (Seyer et al. 2021).
Dogs with MOKCS demonstrated a strong correlation between TBUT and TBUTNI (OSA-Vet®) tests, furthering the utility of the TBUTNI to identify patients with moderate KCS when compared with the traditional TBUT test. However, in other groups the data did not show the same behavior, making it difficult to infer replacement in all situations. Some factors may be related to this correlation divergence, such as the patient’s cooperation when performing the test and the operator’s interpretation. There is a paucity of studies that focus on validating the TBUTNI (OSA-Vet®) with the traditional TBUT, highlighting the need for further studies to explore the utility of the TBUTNI test to evaluate patients with qualitative tear evaluation.
With the exception of TBUTNI (OSA-Vet®), which showed a strong correlation with TBUT in the MOKCS group, the correlation between the results of the other diagnostic tests used and the OSA-Vet® device was low to moderate in all groups. There was a significant difference between TBUT and TBUTNI (OSA-Vet®) tests among all groups with KCS compared to HD, the ability of these non-traditional diagnostic testing to discriminate between healthy, mild, moderate and severe cases was not clear enough to be considered as accurate. Nevertheless, even with this difference, the values obtained in our study were below what the literature considers normal TBUT in dogs. The results found in our study were similar to those found in other studies in which brachycephalic dogs were evaluated, reaffirming that this conformational group has decreased TBUT even without quantitative KCS (Moore et al. 2001; Sebbag et al. 2022; Sebbag and Sanchez 2022).
The results found in our study for TBUT or TBUTNI (OSA-Vet®) tests demonstrated their ability in diagnosing qualitative tear film disorder in brachycephalic dogs. Importantly, the use of either the TFBUT or TBUTNI to evaluate the tear film can facilitate an earlier diagnosis of DED and initiation of treatment at a less advanced stage of disease (Moore et al. 2001; Hisey et al. 2023). An advantage of the TBUTNI (OSA-Vet®) is that there is no interference from factors that may cause an erroneous result at the time of the exam, such as the volume and/or concentration of fluorescein, which may differ, making the TBUT less reliable (Moore et al. 2001; Iwashita et al. 2022; Faghihi and Rajaei 2023). However, the TBUTNI (OSA-Vet) has some subjectivity associated with the measurement as it requires the examiner to manually open the lids and determine the point at which the projected interference patterns demonstrate a disturbance, consistent with the breakup of the tear film.
In conclusion, the results of this study demonstrated that it is not yet possible to replace conventional tests by the OSA-Vet® equipment, however it may be useful as an adjunctive diagnostic test for assessing tear film disorders. Brachycephalic dogs with KCS had comparable results between the TBUT and TBUTNI (OSA-Vet®) tests, demonstrating the potential utility of the TBUTNI (OSA-Vet) to assess tear film quality. Finally, more studies are needed to further validate the OSA-Vet and establishing reference values for different breeds.