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C. Maldonado, M. F. Haddad, P. B. Morgan; In vitro versus in vivo Contact Angles of Hydrogel Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3430.
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To compare contact angles of hydrogel contact lenses obtained in the laboratory to those obtained on-eye.
Sessile drop and captive bubble contact angles were measured in the laboratory (in vitro) for four different hydrogel contact lenses (etafilcon A, balfilcon A, lotrafilcon A and senofilcon A) using an OCA 20 contact angle analyser (DataPhysics Instruments, Filderstadt, Germany). Ten lenses of each lens type were measured three times giving a total of 120 measurements for each technique. All lenses were soaked in phosphate buffered saline (PBS) prior to measurement in order to remove any surfactants from the lens surfaces and deionised water was used as the probe liquid. The on-eye (in vivo) contact angles of the same (PBS soaked) lenses, which were worn by 10 subjects, were measured using novel, custom-designed NOWA instrumentation: Novel On-eye Wettability Analyser (NOWA) at two time points: 30 minutes and 6 hours after lens application. The NOWA instrumentation delivers a drop of 0.4% sodium hyaluronate mixed with sodium fluorescein directly on to the in vivo lens surface whilst a two camera digital system records the resulting contact angles (previous work has shown no statistical difference between in vitro hydrogel sessile contact angles obtained with water and those obtained with the probe liquid used with the NOWA instrumentation).
Contact angles for all lenses using the four different methods were (mean ± standard error): sessile drop (60.7 ± 4.8°), captive bubble (26.6 ± 0.5°), NOWA 30 minutes (17.8 ± 0.9°) and NOWA 6 hours (17.9 ± 0.9°). Contact angles obtained at the two times points using the NOWA instrumentation were similar whilst those obtained with the sessile drop and captive bubble methods were significantly different to each other (p <0.0001) and also to those found with the NOWA technique (p <0.0001).
These data show significant differences in contact angle when lenses are measured in the laboratory compared with in the in vivo, on-eye situation, presumably due to the coating of contact lens surfaces with tear film components. These findings bring into question the utility of laboratory-derived contact angles for predicting how a lens will behave on the eye.
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