A version of the Cambridge Interfacial Tensiometer was built to explore the extensional response of model tear films. In this device, two T-bars are floated in parallel at the air-water interface. One is connected to a motor and the second is attached to a force transducer to measure how adsorbed materials respond when subjected to extensional strains. Several changes were made to the design by Jones and Middelberg (Chemical Engineering Science, 2002) including the addition of a camera to directly observe flow fields in surface structures. In addition, the camera was used to measure the width of the “necking” region, which may be used to calculate two-dimensional extensional viscosity. Before application to complex systems, the tensiometer was used to measure the stress-strain response of purely viscous oils to confirm predicted relationships between extensional viscosity and shear viscosity in two dimensions. Once this correlation was established the tensiometer was used to study model tear film systems. The tear film consists of a lipid layer, which aids in the spreading of the film, a water layer and an oil layer, which prevents evaporation. During a blink the lipid layer is rapidly compressed and expanded on the surface of the eye, and its response under extensional flow will help to understand the role of different compounds in establishing continuity of the tear film.