Kim Miller

Graduate Student, Ph.D. Program

co-advised by Kenneth Polse

Massachusetts Institute of Technology
B.S. Chemical Engineering, 1997

Research Interest:
Tear exchange on the ocular surface
in the presence of a Soft Contact Lens

Funding Sources:
National Institute of Health, National Eye Institute
Bill & Melinda Gates Fellowship

kmiller@spectacle.berkeley.edu

Radke Lab Home Page

Current Project:

Efficient tear exchange under a soft contact lens (SCL) may be necessary to avoid some of the adverse events associated with SCL extended wear. Current SCL exhibit low tear exchange, and fitting strategies to increase tear mixing have not been successful. It has been suggested that multiple fenestrations near the lens periphery may increase tear exchange under a SCL by increasing the transverse travel, which facilitates tear pumping. To test this model, we measure the effect of fenestrations on tear exchange under a SCL. Tear exchange is estimated using a scanning fluorophotometer to measure the exponential depletion of fluorescein, (FITC-Dextran) under the lens; tear exchange is expressed as the time in minutes to deplete 95% of dye (T95). Twenty subjects were fitted with 2 pairs of identical hydrogen-silicon SCL (lotrafilcon A) except that the experimental lens had 40 fenestrations (Dholes ~ 100 µm) placed in 2 concentric rows in the mid periphery. Each subject was measured with both fenestrated (F) and un-fenestrated (uF) lenses; the order of lenses and eye tested were randomly assigned. Subjects rated comfort on a scale of 0 to 50 (50=very comfortable); subjects with comfort <35 were excluded. The T95 estimates were significantly lower (P<0.001) for the F(meanT95=18.8 min) lenses compared to the uF(meanT95=23.0 min) lenses (δT95=4.9 min , 95% CI=2.9, 6.8); and lens comfort did not differ between the two lens types (p = 0.77). Our results agree with theoretical predictions that fenestrations will increase tear mixing without adversely affecting comfort.

Project Designs:

Changes in contact lens design that increase the tear exchange under a contact lens may reduce the frequency of complications associated with SCL. The design of the lenses used in the previously described study are shown here. In the future we would like to improve upon this design by strategically placing the fenestrations where the tear film is thinnest, where it will have a greater impact on improving the flow under the contact lens.