Fig. 4

Grading scale of interferometric patterns. A four-interval grading scale of interferometric patterns was adopted from human literature and one more grade (grade 0) was added to evaluate lipid layer (LL) thickness in dogs. Grade 0 includes cases of almost complete absence of the aqueous phase, with lipid-contaminated mucus over the surface of the corneal epithelium. Grade 1 (15–30 nm) corresponds to faintly visible homogeneous meshwork pattern; grade 2 (31–60 nm), when a more compact meshwork pattern with grey waves and occasional colored shades is observed; grade 3 (61–100 nm), when a meshwork with waves and interference fringes with some colors are noted and grade 4 (more than 100 nm), when waves with many colors are present