The tear film on the eye is an ultrathin layer of fluid that protects the cornea and keeps vision sharp. It’s usually pictured as a perfectly smooth surface, but the real cornea, even a healthy one, is covered in microscopic bumps. In a new study, researchers built a model that includes this roughness, as well as fluid slipping along the surface, molecular attraction forces, and lipid transport at the air interface.

The model showed: the larger the amplitude of the irregularities, the faster the film loses stability and breaks. The calculations matched experimental data. It turned out that the breakup location depends on the initial perturbation, while the breakup time depends on the slip coefficient, roughness amplitude, and initial film thickness.

These results explain why contact lenses sometimes fail to stay on the eye. Understanding how corneal roughness affects the tear film could help design more comfortable lenses and eye drops.