Although the structure of the tear film is well understood, The exposed part of the eyeball is covered by a tear film, which how the 10-mm thickness actually arises remains an open is vital for the proper function of the eye. The film thickness has question. In a complete blink, the upper eyelid lowers, been measured to be roughly 10 mm; however, how a tear film of touches the essentially stationary lower lid, and then rises this thickness is generated has not been clearly explained. It is to the fully opened position (3,8). The commonly accepted proposed that the tear film is deposited analogous to a coating tear-film formation model (2, 9) argues that the rapidly risprocess by the rising meniscus of the upper lid during a blink. A ing upper lid leaves behind a layer of tear fluid whose thickcoating model is formulated that not only predicts correctly the ness is much less than that of the final tear film. Subsefilm thickness, but also captures the postblink lipid spreading commonly observed in experiments. A deposited tear film thins rapidly quently, surface tension-driven upward motion of the oily near the tear meniscus surrounding the film. Numerical simulation layer drags tear fluid from the meniscus of the lower lid and of this thinning reveals that the minimum film height obeys a thickens the tear film to its final value (10). However, there power law. When the minimum height reaches the effective range is no experimental evidence that the film left behind by the of dewetting intermolecular forces, the film ruptures. The thinning upper lid is much thinner than 10 mm. Most importantly, time therefore defines a breakup time, and the thinning law shows the leave-behind mechanism is not explained, so the film explicitly how this breakup time is related to tear viscosity, surface thickness cannot be predicted theoretically.
tension, meniscus radius, and initial and final film thicknesses.
We propose that the tear film is directly deposited at close
The calculated breakup time agrees with those observed experito 10 mm in thickness by the rising meniscus of the upper mentally.