Contact lens in vitro wettability by interferometry measures of drying dynamics

Purpose: To develop with a thin film interferometer new parameters to describe the drying properties of contact lenses; these are: time to first break-up (onset latency), duration of lens surface drying (drying duration), maximum speed of increase in the drying area (maximum speed), and the time to reach maximum drying speed (peak latency). These new parameters were compared with the contact angle (CA) measurement of contact lenses by the captive bubble (CB) technique.
Methods: A thin film interferometer was connected to a digital camera, which captured images of the pre-lens liquid film of seven soft contact lenses in vitro: 1-Day Acuvue Moist, ACUVUE Oasys (Johnson & Johnson Vision Care); SofLens 38, PureVision (Bausch & Lomb); AirOptix Night & Day, AirOptix Aqua (CIBA Vision, Corp); and Proclear (Cooper Vision). The images were obtained from the lens surface when it was wet until it became dry (7 images per second) to generate video clips. A program was created in MATLAB to analyze the results. The CAs of the lens surfaces were measured by the CB technique with an OCA-20 contact angle analyzer (Data Physics Instruments).
Results: There were no significant relationships found between the CA and the new drying parameters (P . 0.05). Analysis of the results using analysis of variance and post hoc tests showed that the surface drying dynamics measures effectively differentiated between more of the soft lenses than the CA.
Conclusions: A new technique is described for assessing the drying characteristics of contact lenses by observations of the pattern, size, and speed of pre-lens liquid film break-up observed by a thin film interferometry. The interferometry method allowed evaluation and differentiation between lens materials. This new technique has the major advantage that it can be applied to evaluate contact lens wettability in vivo and in vitro.