“Exchange of tear film in the gap between a contact lens and the eye” Ioanna Stamati, Philips Applied Technologies- National Technical University of Athens.
Abstract:
Contact lenses are worn predominantly in order to correct for aberrations of the eye. Movement of the lens over the eye, for example during a blink motion of the eyelids or a change in the gaze direction, is detrimental to the optical performance and in general should be minimized. Clinical experience indicates that no lens movement initially provides good comfort. However, such a non-moving lens later causes discomfort through accumulation of debris, acidity, poor hygiene etc. A "healthy fit" lens is considered by practitioners to be one with adequate movement during blinking, because this enhances the exchange of the tear film between the eye and the lens.
During blinking the eyelids exert a varying pressure on the lens, which causes the tear film to be sucked into or squeezed out of the gap between the contact lens and the eye. The lateral motion of the lens causes an exchange of the tear film through the shearing motion of the lens.
In this talk an approach is presented to study the exchange of tear film in the gap between a contact lens and the eye. In this approach the “spherical curved” contact lens-eye geometry is simplified to a flat disc placed on an infinite flat plane with a thin tear film in between them. The normal force exerted by the upper eyelid on the lens is modeled as a transient moving normal force acting at the lens. The Reynolds equation (combination of the Navier-Stokes equation and the continuity equation), which is well known in lubrication theory, is used to describe the tear film flow, as the tear film thickness is much smaller than the dimensions in the plane of the lens.
A finite element method is used to solve the Reynolds equation. Results will be shown for the squeeze motion of the lens, the pressure build up in the tear film,the tear film flow and the tear film exchange during a blink.
Two OPTEC professors have been awarded three "Gouden Krijtjes", the yearly teaching awards given by the organization of engineering students (vtk). Prof. Lombaert was awarded the prize for the best course in civil engineering, and Prof. Diehl the prizes for the best professor and the best course in mathematical engineering (where he teaches numerical optimization). They received these awards at the yearly "proffentap" where experienced students taught them how to draft beer professionally.
