American Board of Opticianry (ABO) Practice Test

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What does specific gravity measure in the context of optometry?

A. Brightness of light passing through a lens
B. Thickness of a lens
C. Weight of a lens
D. Dispersion of light by a lens

The correct answer is: B. Thickness of a lens

Specific gravity measures the density or relative weight of a substance compared to water. In the context of optometry, it refers to the thickness of a lens. The other options are incorrect because specific gravity does not measure brightness or dispersion of light passing through a lens, nor does it directly measure the weight of a lens. While the weight of a lens may be affected by its specific gravity, it is not the main factor being measured in this context. Additionally, while thickness is related to weight, it is not the primary factor being measured when using specific gravity in optometry.