Variations in the tear film lipid layer by age in healthy brachycephalic dogs

This cross-sectional study evaluates the morphological and qualitative changes in the meibomian glands (MGs) and tear film lipid layer (TFLL) associated with aging and sex in canine brachycephalic breeds. One hundred and eleven brachycephalic dogs with normal eyes were included. Dogs were divided into three age groups: ≤4 years (G1), >4 and < 10 years (G2) and ≥ 10 years (G3). Schirmer test I (STT I), upper eyelid MGs noncontact infrared meibography (NIM), tear interferometry (TFI) and tear film breakup time (TFBUT) were performed in each eye. Loss of MGs and lid margin abnormalities (LMAs), as well as TFI patterns were scored from 0 to 3 depending on severity. Normality was assessed with the Shapiro-Wilk test. The Kruskal-Wallis test was used for the analysis of variance among groups. Pearson's or Spearman's correlation coefficient was used to assess the correlation between MG loss and STT I values. Significance was set at p < 0.05. Forty-four Shih-Tzus, 37 Pugs and 30 French Bulldogs were enrolled in the study. Median age was 39.5 months (range 30–48 months) in G1, 94.5 months (range 65–118 months) in G2, 154.5 months (range 120–201 months) in G3. Loss of MGs was statistically higher in G2 and G3 (p < 0.001) and was associated with a reduction in TFI scores (p < 0.001) and STT I (p < 0.001). Loss of MGs was then negatively correlated with TFBUT. No statistical differences were associated with sex (p > 0.05) or breed (p > 0.05). The tear film lipid layer appears to be negatively affected by age in brachycephalic dogs.