ballast
(bal'ăst),1. Material of doubtful value itself used to stabilize something (for example, maritime practice). 2. Something largely without intrinsic value.
Farlex Partner Medical Dictionary © Farlex 2012
ballast
Additional weight of material incorporated in a part of a contact lens to maintain it in a given orientation (Fig. B1). This is often provided by giving prismatic power to the lens (prism ballast lens).
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Fig. B1 Truncated and prism-ballasted toric contact lens
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann