A collaborative study conducted by researchers at the University of California, Berkeley, School of Optometry and Department of Chemical Engineering has resulted in a new contact lens design for potentially safer long-term wear.
Professors Kenneth Polse (Optometry) and Clayton Radke (Chem. Eng.), and former graduate student Kimberly Miller, PhD, have developed hydrodynamic models to improve tear mixing. Clinical tear-mixing measurements have confirmed these models, which involve the effects of laser-drilled fenestrations (holes) on tear mixing in the tear film behind soft contact lenses.
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| Representative, cylinder-shaped fenestration in a dehydrated soft contact lens (magnification = 25X). |
Schematic of a 13.8 diam. lens with 2 rows of 20 holes each, showing placement of inner and outer rings. |
Although the FDA has, for decades, approved some contact lens designs for extended wear (sleeping while wearing lenses), a number of potential complications may result from inadequate tear flow. During sleep, metabolic debris accumulates on the eye and may become trapped under the contact lens. Adverse ocular responses may occur if the lenses are inefficient in flushing out the debris upon opening the eyes after sleep.
The research team hypothesized that strategic placement of holes in contact lenses might enhance tear mixing by inducing increased transverse ("in-out") movement, which does not cause discomfort for lens wearers (in contrast to lateral or "up-down" movement).
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Diagram of transverse ("in-out") movement of contact lens with (R) and without (L) fenestrations (holes)
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Tear mixing (or fluid flow) behind the lens was measured by determining how long it took to remove 95% of a fluorescent tracer dye instilled in the tears.
The results were promising, with a 20-25% increase in tear mixing. While it is too soon to assess the potential for commercial contact lenses with fenestrations designed in this manner, professors Polse and Radke plan additional testing of their tear-mixing models and related clinical measurements.
An article about this research by Miller, Polse, and Radke, titled "Fenestrations enhance tear mixing under silicone-hydrogel contact lenses," has been published in Investigative Ophthalmology & Visual Science, Jan. 2003, Vol. 44,
no. 1. pp. 60-67.
An article about this research written by Justin Lee ( "New Contact Lens Design May End Daily Hassles") appeared in the Daily Californian on February 12, 2003.
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